Ministry of Health NZ - TACK...1. INTRODUCTION 1.1 Consumer perception of drinking-water quality The consumer of drinking-water relies completely upon his senses to assess its quality

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DRINKING-WATERSTANDARDS FORNEW ZEALAND

A report prepared for the Board of Health by theDepartment of Health

WELLINGTON 1984

LIBRARYDEPARTMENT OF HEALfl

WELLINGTON

FOREWORDIt is significant and appropriate that the first technical publication of

the reconstituted Board of Health should deal with the most fundamen-tal of all health needs—the supply of safe drinking-water.

Originally commissioned by the previous Board of Health, the docu-ment has been prepared in close accordance with the recent guidelinespublished by the World Health Organisation in a form which makes itreadily available to all water supply authorities in New Zealand. It isprobably the first such national document anywhere in the world, andrepresents a significant contribution to the International Drinking-Waterand Sanitation Decade.

I am confident that adherence to the water quality standards and mon-itoring and surveillance programmes specified in this publication willprovide an ongoing assurance of safe drinking-water for the New Zealandpublic. I commend it to local authorities throughout the land.

D. ShortChairmanBoard of Health

August 1984

PREFACE

In 1960 the former Board of Health adopted the World Health Organ-isation's International Standards for Drinking-Water as the criteria forthe quality of drinking-water in New Zealand and since then the Depart-ment of Health has used them for assessing the quality of wholesomedrinking-water.

In 1978, following the growing concern of member countries about thelikely health effects of trace levels of inorganic and organic substancesin drinking-water, WHO convened a number of Task Groups to reviewthe International Standards for Drinking-Water. New Zealand expertshave contributed to and reviewed the work of the Task Groups throughthe Department of Health's role as a national focal point for the WHOEnvironmental Health Criteria Programme. The result of the compre-hensive studies has now been published as Guidelines for Drinking- WaterQuality.

The WHO Guidelines have been used as recommended by WHO, forthe preparation of standards for drinking-water quality which are suit-able for New Zealand. As some of the substances for which guidelinevalues are given are absent from or unlikely to be present in New Zealanddrinking-water they have been omitted. Others which are peculiar toNew Zealand have been inserted.

As more information about the presence in New Zealand of other toxicsubstances is received, amendments to the Drinking-Water Standards forNew Zealand will be issued.

As explained in the text, the standards should be regarded as givinglevels of concentration of substances, on which further action should bebased and not as absolute maxima.

The Board of Health recommends the study and use of the Drinking-Water Standards for New Zealand as the basis for the production anddelivery of wholesome drinking-water in New Zealand.

The Drinking-Water Standards for New Zealand have been preparedfrom the WHO Guidelines for Drinking- Water Quality 1984, by Mr R.R. L. Harcourt, C.Eng., M.I.C.E., M.I.P.E.N.Z., M.R.S.H.

A draft of the Drinking-Water Standards for New Zealand was cir-culated to water engineers and analysts in New Zealand and their com-ments have been considered in preparing the published version. Theparticular assistance given by the Ministry of Works and Developmentand the Department of Scientific and Industrial Research is gratefullyacknowledged.

DRINKING-WATER STANDARDS FORNEW ZEALAND

CONTENTSPage

1. Introduction ......1.1 Consumer perception of drinking-water quality

1.2 Objective of the Standards . .. .1.3 Priority for assessment of water quality1.4 Basis for Drinking-Water Standards for New Zealand..21.5 Nature of Drinking-Water Standards for New Zealand21.6 Types of contaminants affecting drinking-water quality3

1.6.1 Microbiological contaminants .. 31.6.2 Other pathogenic organisms. . 41.6.3 Chemical contaminants of health significance4

1.6.4 Aesthetic and organoleptic factors 61.6.5 Radioactive contamination 6

1.7 Summary tables of guideline values.. 61.8 Application of the Drinking-Water Standards for New

Zealand ...... 13

1.8.1 Laws, regulations and standards.. 131.8.2 Compliance and surveillance.. 14

1.8.3 Remedial action.... 201.8.4 Special considerations for small rural water

supplies. .. .. ... 212. Microbiological Aspects.... 22

2.1 The bacteriological quality of drinking-water.. 22

2.1.1 Introduction ...... 22

2.1.2 Guideline values. .. .. 23

2.1.3 Frequency of sampling.... 262.1.4 Collection, storage, and transport of water samples

for bacteriological examination . .. . 282.1.5 Techniques for the detection of coliform organisms28

2.2 The virological quality of drinking-water.. 312.3 Nature of the guideline values.... 312.4 Test methods...... 32

3. Biological Aspects. .... .. 333.1Protozoa ......... 33

3.1.1 Piped and unpiped supplies.. 333.1.2 Monitoring...... 33

3.2 Helminths........ 33

3.3 The free-living organisms .....: 34

DRINKING-WATER STANDARDS FOR NEW ZEALAND

4. Chemical and Physical Aspects 354.1 Introduction... 35

4.1.1 Nature of the guideline values 354.1.2 The health effects of chemical contaminants354.1.3 Basis of guideline values 36

4.2 Health-related inorganic constituents 374.2.1 Guideline values recommended.. 374.2.2 Boron...... 37

• 4.2.3 Fluoride.... 374.3 Health-related organic contaminants 38

4.3.1 Reservations relating to the guideline values384.3.2 Associated risks of lowering organic contamination38

4.3.3 Basis for guideline values.. 394.3.4 Variations in listed substances .. 39

4.4 Aesthetic and organoleptic aspects 404.5 Monitoring.... 424.6 Remedial measures... ... 42

4.6.1 General..... 424.6.2 Corrective measures for chemical constitutents of

health concern. .. .. 434.663 Corrective measures related to the aesthetic quality

of drinking water.. 445. Radioactive Materials in Drinking-Water 46

5.1 Introduction. .. .. .. . 465.2 Nature of the guideline values. . 465.3 Guideline values recommended.. 47

5.4 Interpretation of guidelines. .. .. . 47

References. ... .. .. 48

LIST OF TABLESPage

Table 1 Microbiological and biological quality.Table 2 Inorganic constituents of health significance 10Table 3 Organic constituents of health significance. . 10Table 4 Aesthetic quality. .. .. 11

Table 5 Radioactive constituents . .. .. 13

1. INTRODUCTION

1.1 Consumer perception of drinking-water qualityThe consumer of drinking-water relies completely upon his senses to

assess its quality. Water constituents may effect the appearance, smellor the taste of the water and the consumer will evaluate the quality andthe acceptability essentially on these criteria.

Water having a high turbidity, being highly coloured or having anobjectionable taste, will give the consumer the impression that dangerouscontaminants are present, leading to a refusal to drink such water anda possible turning to less wholesome water.

However, people can no longer rely entirely upon their senses as acriterion of quality judgement. Today we are aware that the absence ofany adverse sensory effects does not guarantee the safety of drinking-water.

1.2 Objective of the StandardsWater for drinking and other domestic uses should be safe, palatable,

and 'aesthetically pleasing. It should be free from pathogenic organismsand their indicators, deleterious concentrations of chemical substances(including radioactive materials), and objectionable colour, odour, tasteand turbidity. Corrosiveness, scale forming tendencies and excessive soapor detergent consumption due to hardness, should be controlled toacceptably low levels.

The primary aim of the Drinking-Water Standards for New Zealandis the protection of public health (as defined by WHOA) and thus theelimination, or reduction to a minimum of those constituents in waterknown to be hazardous to the health and well-being of the community.

1.3 Priority for assessment of water qualityThe microbiological quality of drinking-water is of prime importance

and must never be compromised in order to provide aesthetically pleas-ing and acceptable water.

Chemical contaminants are not normally associated with the acutehealth effects caused by micro-biological contaminants, and conse-quently their control is of less importance than indicators of diseaseorganisms.

a Health is a state of complete physical, mental and social well-being and not merelythe absence of disease or infirmity.

A


1.4 Basis for Drinking-Water Standards for New ZealandDrinking-Water Standards for New Zealand are derived from the World

Health Organisation's "Guidelines for Drinking- Water Quality' and arebased on an appreciation of local conditions of topography, land use,natural water quality, laboratory facilities and other relevant factors.

In developing the values given in the WHO Guidelines for Drinking-Water Quality the organisation established Task Groups which, duringthe period 1978 to 1982 studied previous editions of WHO drinking-water quality standards, Environmental Health Criteria documents foreach constituent, and other relevant reports of WHO working groups.Some of the information supporting the recommendations is quoted inthis document and the rest may be found in the 3 volumes of the WHOGuidelines for Drinking- Water Quality. Criteria monographs for each ofthe constituents and parameters examined constitute Volume 2 of theWHO Guidelines, whilst Volume 3 contains recommendations andinformation concerning what needs to be done in small communitiesand in rural areas to safeguard the water supplies.

1.5 Nature of Drinking-Water Standards for New Zealand(a) The quality of water defined by the Drinking-Water Standards for

New Zealand is such that it is suitable for human consumption and forall usual domestic purposes. However, water of a higher quality may berequired for some special purposes, such as renal dialysis.

(b) Drinking-Water Standards for New Zealand are compriseã ofguideline values for limits of concentration of organisms and substanceswhich affect water quality.

A guideline value represents a concentration or a number which ensuresan aesthetically pleasing water and does not result in any significant riskto the health of the consumer.

(c) When a guideline value is exceeded this should be a signal:(i) to investigate the cause with a view to taking remedial action;(ii) to consult with the Department of Health for advice.

(d) The guideline values should be considered as only one specialisedaspect of the range of requirements which should be satisfied in orderto ensure a safe, satisfactory and aesthetically pleasing water supply. Itis essential to appreciate that the Standards assume a raw water sourcewhich is, at worst, not heavily polluted by municipal, industrial or agri-cultural wastes, and should preferably be as unpolluted as practicallyattainable. Accordingly, guideline values are specified for only a limitednumber of a wide range of potential hazards, which might arise in heav-ily polluted waters.

(e) While some of the guideline values for aesthetic quality provide forcontrol of common causes of taste, odour, appearance and corrosionproblems, the very wide range of possible causes precludes the provisionof comprehensive guideline values covering all causes, even for relativelyunpolluted sources of water. Accordingly some aesthetic and corrosion

2

)

1. INTRODUCTION

problems may be encountered in some supplies, even though thereappears to be full compliance with all numerical guideline values.

(j) Although the guideline values specified have been derived to safe-guard health on the basis of lifelong consumption, short-term exposuresto higher levels of chemical constituents may be tolerated. The amountby which, and the duration for which, any guideline value can be exceededwithout affecting the health of the public depends on the specific sub-stance involved.

(g) In the case of radioactive substances, the term guideline value isused in the sense of a "reference level" as defined by the InternationalCommission on Radiological Protection (ICRP).

(h) Although the guideline values describe a quality of water which isacceptable for lifelong consumption, the establishment of these Stand-ards should not be regarded as implying that the quality of drinking-water may be degraded to the recommended level. Indeed, a continuouseffort should be made to maintain a drinking-water quality at the highestlevel attainable.

1.6 Types of contaminants affecting drinking-water quality

1.6.1 Microbiological contaminants

Microbiological contamination of a water supply has by far the great-est potential for causing sickness and even death within the community,a fact which has long been established beyond question. Although thetransmission of diseases through a water supply requires the presence ofspecific pathogenic organisms (e.g., S. Typhi, Vibrio cholera, Hepatitisviruses), tests for individual types of such organisms are too complexand often too insensitive and slow to provide a practical means of mon-itoring and control. Since the entry of pathogenic organisms to a watersupply is always accompanied by a much larger number of bacteria char-acteristic of faecal pollution, the absence of such bacteria can reliably betaken to indicate the absence of pathogenic microorganisms. The use offaecal coliform and coliform organisms I as indicator bacteria in accord-ance with the guidelines set out in Table 1 is very firmly established asan effective monitoring procedure to assure protection of the communityfrom water-borne disease.

Microbiological contamination can produce infections immediatelyafter consumers drink. Accordingly every effort should be made to com-ply with the guideline values at all times. Immediate action is requiredto identify the causes of non-compliances and correct them.

Monitoring for indicator bacteria and, if appropriate, free availablechlorine, turbidity and pH should be accorded the highest priority.

Guideline values for control of microbiological quality are set out inTable 1.


1.6.2 Other pathogenic organismsSome pathogenic protozoa, and helminths, and other undesirable

organisms may be present in water supplies, but cannot be detected byenumeration of indicator bacteria or other methods suitable for routinemonitoring. Selection of suitable water sources and appropriate treat-ment methods are required to ensure the absence of such hazards.

Guidelines for control of biological quality are set out in Table 1.

1.6.3 Chemical contaminants of health significanceThe fact that chemical contaminants are not normally associated with

acute effects places them in a lower level of priority than microbiologicalcontaminants, the effects of which can be immediate and massive. It canbe argued that chemical standards for drinking-water are almost irrele-vant where gross bacterial contamination occurs. A consequence of thelong-term nature of any hazard associated with chemical constituents, isthat the values recommended relate to an average level of exposure.Occasional small excursions above the level are acceptable, subject tolocal detailed consideration of their implications. This is made clear inthe definition of the guideline values for chemical substances.1.6.3.1 Inorganic constituents of health significance

Definite toxic effects in man have been established for all the inorganicconstituents of health significance listed in Table 2. In all cases, the limitsset take into account extensive information about the adverse healtheffects arising from industrial exposure and/or the consumption of wateror foods containing the constituents at levels considerably higher thanthe guideline values. Derivation of the values assumes the continual dailyconsumption of 2 litres of water by a 70 kg man, and considers the totalintake from food, air and water. Somewhat arbitrary factors, such as 10or 100, are applied to the lowest exposures giving detectable adverseeffects, and the water guideline is commonly set at some fraction of thetotal acceptable daily intake. Accordingly the guideline values are regardedas having a firm basis of observed health effects in man, and involveonly modest extrapolations from the lowest levels showing definiteeffects.'

Although occasional small excursions above the guideline values areacceptable, subject to local detailed consideration of their implications,the long-term average concentrations for these constituents should notexceed the guideline values.

In general, inorganic constituents of health significance are not likelyto be present in New Zealand water supplies at levels exceeding a smallfraction of the guideline values, unless there are potential sources whichare likely to be identified in sanitary surveys (e.g., geothermal discharges,mining activity, intensive agriculture or horticulture). Similarly, they areunlikely to appear suddenly and unexpectedly at levels which are likelyto cause problems. Accordingly, sampling and analysis is required muchless frequently than is required to ensure adequate microbiological quality.

4

1. INTRODUCTION

The range of constituents listed in Table 2, coupled with the relativelylow concentrations specified, makes reliable analyses for them moder-ately difficult, and most local authorities would not be expected to estab-lish their own laboratory facilities for these determinations, but to relyon the services provided by existing major laboratories.

1.6.3.2 Organic constituents of health significanceThere is direct or indirect evidence that all the organic substances forwhich guideline values have been recommended in Table 3 can causeharmful effects and all are known to occur in water.

The guideline values for these organic constituents are based on evi-dence of either toxicity or carcinogenicity, and the derivation proceduresare different in the two cases.

For the toxicity-based guidelines (i.e., chlordane, 2,4,5-T, 2,4-D, DDT,Diquat, Lindane, Methoxychlor, Paraquat, pentachiorophenol) the pro-cedure followed is similar to that described above (in 1.6.3.1 InorganicConstituents of Health Significance). However, there is a much greaterreliance on animal, rather than human toxicity data and because of theadditional uncertainty this introduces, the safety factors applied are larger(e.g., 1000 or more).

For the carcinogenicity-based guidelines (i.e., benzene, benzo-a-pyrene,chloroform, hexachlorobenzene, tetrachloroethene, trichloroethene, 2,4,6trichiorophenol), the derivation of the guideline values relies almostexclusively on animal carcinogenicity test data, and includes extrapo-lations to exposures about 100,000 times lower than the lowest exposuresgiving measurable cancer incidence. There are a number of major uncer-tainties in arriving at the guideline values, which are the subject of con-troversy within the scientific community.

The guideline values calculated by WHO correspond to a maximumadditional cancer risk of 1 in 100 000 per life time, or, in other words,a risk of one additional cancer victim every two years if every NewZealander drinks 2 litres of water containing one of the specified organicchemicals at the guideline value, daily, throughout his lifetime. While amaximum additional cancer risk can be calculated, it is also not possibleto prove that there is any cancer risk at all, even at substantially higherconcentrations than those of the guidelines.

In view of the relatively low risk for which the guideline values arecalculated, and the uncertainty associated with them, the values shouldbe regarded as desirable levels which should not, on average, be grosslyexceeded. It would be prudent to adopt readily available and practicalmeasures to decrease excessive levels, but other health protection meas-ures (e.g., chlorination) must not be compromised and major additionalexpenditure on such measures as new treatment processes, would notusually be justified, solely to control these contaminants.

Analysis for the Organic Constituents of Health Significance in Table3 is particularly demanding in terms of technical skill and instrumen-tation required and is also time consuming compared with analyses for


most inorganic chemicals. Analyses would usually be required only wheretheir presence is suspected and for these constituents, should be under-taken only in major national laboratories.

1.6.4 Aesthetic and organoleptic factorsTable 4 sets out water quality factors likely to affect the consumer's

appreciation of the water, or the integrity of the distribution system.Generally there are no adverse health effects associated with the con-stituents unless the concentrations far exceed the limits specified here,which are based on undesirable effects such as tastes and odours, dis-colouration and blockages or corrosion of pipes.

A number of the parameters (e.g., pH, turbidity, colour, iron, man-ganese and aluminium) may be required for effective control of treat-ment processes and it will be essential for local authorities operating suchtreatments to have ready (and perhaps on-site) access to analytical facili-ties for the appropriate constituents.

The requirement for ready access to analytical facilities for the aes-thetic quality parameters in other circumstances will depend on the extentto which they are a problem and are amenable to control in the particularsupply. The local authority is the agency primarily responsible for thesupply of satisfactory water and handling of consumer complaints.Accordingly if, for example, a supply is known to give problems of iron,copper or zinc contamination, perhaps as a result of a corrosive water,the local authority will need access to analyses for these and other relatedconstituents to assess the level and distribution of the problems, identifylikely causes and devise remedial measures.

Unlike chemical constituents of health significance, for which averagelevels are more important than short-term concentration peaks, for manyof the aesthetic factors it is precisely the peak concentrations and theirfrequency of occurrence which give rise to consumer complaints. If aparticular constituent is known to cause problems, it is therefore neces-sary to monitor the supply frequently and comprehensively if a reason-ably accurate assessment of the extent of the problem is required.

1.6.5 Radioactive contaminationTable 5 sets out maximum recommended levels of radioactivity in

drinking-water, and has been included for the sake of completeness. Theabsence of any significant sources of radiation in the New Zealandenvironment provides an assurance of quality well within these levels.

1.7 Summary tables of guideline valuesGuideline values in the summary tables should be used and inter-

preted in conjunction with the appropriate section of the informationcontained within the Standards. Test results which show that guidelinevalues are being exceeded, indicate the need for remedial action, therelative priority for which is:

6

1. INTRODUCTION

(a) The detection in a water, supply of the indicator organisms shownin Table 1 warns of the possibility of the spread of disease by the watersupply and should be followed by urgent remedial action.

(b) The guideline values for the substances listed in Table 2 are basedon health risks calculated for lifetime consumption. If test results in the5-yearly surveillance programme conducted by the Department of Healthshow the presence of these substances at levels approaching the guidelinevalues, or if there are other indications of their likely presence, morefrequent monitoring should be introduced to assess whether the averagelevel in fact exceeds the guideline. At the same time investigations toidentify the source of the contaminant(s) and possible remedial measuresshould be undertaken.

(c) It is unlikely that many of the substances listed in Table 3 will befound in New Zealand water supplies. The guideline values are calcu-lated with large factors of safety, from the results of laboratory tests onanimals. The analytical methods necessary for the detection of the guide-line values of most of the substances in , Table 3 are complex and costlyand available at only a few laboratories in New Zealand. Consequentlyanalyses are likely to be done only when the presence of a substance issuspected.

(ci) Table 4 includes parameters which are likely to affect the con-sumers appreciation of drinking-water quality. Many of the necessarytests will be conducted as part of the water supply authority's routinecontrol of water treatment processes.

A "two-level" system of guideline values is used in Table 4 becauseof the nature of the parameters. ."Highest desirable" applies to a waterwhich would be generally acceptable to consumers. Values greater thanthose listed under "Excessive level", would markedly impair the pota-bility of the water.

(e) The surveillance of radioactivity in public water supplies is theresponsibility of the National Radiation Laboratory of the Departmentof Health, and the occurrence of radionuclides at levels in excess of theguideline values in Table 5 will be detected by the laboratory's normalenvironmental monitoring systems. Advice on any remedial actionnecessary will be given by the laboratory.


Table 1. Microbiological and Biological QualityDocument Reference

Guide- WHOOrganism Unitline Remarks N.Z.Guide-value StandardslinesVol. 1

I. Microbiological quality

A. Piped water supplies

A. I Treated water entering the distribution systemfaecal coliformsnumber/nilfor effective disinfection2.1.12.1.1

100 ml turbidity < 1 NTUB; for2.1.2.1.12.1.2.1disinfection with chlorine,pH preferably < 8.0, freechlorine residual 0.2-0.5gfm3 after 30 minutes(minimum) contactb

coliform organismsnumber!nil100 ml

A.2 Untreated water entering the distribution systemfaecal coliformsnumber!nil

100 ml

coliform organismsnumber/nilin 98% of samples exam-2.1.2.12.1.2.1100 ml med throughout the year—

in the case of large sup-plies when sufficient sam-ples are examined

coliform organismsnumber/3in occasional sample but100 ml not in consecutive sam-

ples taken within 3 days

A.3 Water in the distribution systemfaecal coliformsnumber!nil 2.1 .2.1.3 2.1.2.1 (c)

100 ml

coliform organismsnumber/nilin 95% of samples exam-100 ml ined throughout the year—

in the case of large sup-plies when sufficient sam-ples are examined

3 in occasional sample butnot in consecutive sam-ples taken within 3 days

B. Unpiped water suppliesfaecal coliformsnumber!nil 2.1.2.22.1.2.2

100 ml

8

1. INTRODUCTION

Table 1. Microbiological and Biological Quality—continuedDocument Reference

Guide- WHOOrganism UnitlineRemarks NZ Guide-value StandardslinesVol. 1

coliform organismsnumber!100 ml

C. Drinking-water containers

faecal coliformsnumber/100 ml


10 should not occur repeat-edly: if occurrence is fre-quent and if sanitaryprotection cannot beimproved an alternativesource must be found ifpossible

nilsource should be free from2.1.2.3

2.1.2.3faecal contamination

nilcriteria do not apply tocommercially bottledwater, which should com-ply with the requirementsof the Food and DrugRegulations 1973

niladvise public to boil water2.1.2.42.1.2.4in case of failure to meet

nilguideline values

nilconsidered achieved when2.2

2.2source is free from wastewater and protected fromfaecal contamination ORby effective disinfectionwith turbidity < 1 NTU,pH < 8.0 and free chlor-,meresidual0.5 g/m3following30minutes(minimum) contact

D. Emergency water supplies

faecal coliformsnumber!100 ml


E. All supplies

enterovirus -

II Biological quality

protozoa (pathogenic)-nilshould be nil: detection3.13.1methods unsuitable for

helminths (pathogenic)-nilroutine monitoring3.23.2free-living organisms-noshould be absent from3.33.3(algae, others) guide- drinking-water: insufficient

linedata available to relatevalue population densities to-setspecific health effects

Nephelometric Turbidity Unit.b The higher chlorine residual is desirable for water from unprotected sources.

9


Table 2. Inorganic Constituents of Health SignificanceDocument Reference

Guide- WHOConstituent0UnitblineRemarks N ZGuide-value StandardslinesVol. 1

arsenic g/m30.05 4.2.2.1boron g/m30.5safe level for human intake4.2.24.2

is 5 g/m 3, but some glass-house plants are dam-aged above 0.5 g/m3

cadmium g/m30.005 4.2.2.5chromium 9/M30.05total chromium 4.2.2.6cyanide g/m30.1 4.2.2.7fluoride g/m30.9 to 1.1 deliberately added fluoride4.2.34.2.2.8lead g/m30.05 4.2.2.10mercury g/m30.001 4.2.2.11nitrate g/m3(N)10above the guideline value 4.2.2.13

health of bottle-fed infantsis likely to be at risk

selenium g/m30.01 4.2.2.14

Constituents of possible health significance not in the table are discussed in Section 4.2.b 9/M3 = mg/I = ppm. (parts per million).

Table 3. Organic Constituents of Health SignificanceDocument Reference

Guide-Constituent0UnitblineRemarks N.Z.Guide-value Standardslines

Vol. 1

aldrin and dieldrinMg/M30.3guideline value applies to4.3.4.14.3.7.4either or both combined

benzene Mg/M310C4.3.7.7

benzo[a]pyreneMg/M30.01 C4.3.7.3chlordane Mg/M30.3 4.3.7.4chloroform Mg/M330cdisinfection efficiency must4.3.4.64.3.7.8

not be compromised whencontrolling this parameter

2,4,5-T mg/m310 4.3.7.6

2,4-D Mg/M3100d 4.3.7.4DOT and breakdown Mg/M31 4.3.7.4products

diquat Mg/M360value set in case of4.3.4.4improper use of diquat incatchment

10

1. INTRODUCTION

Table 3. Organic Constituents of Health Significance—continuedDocument Reference

ConstituentaUfljtbGuide-

lineRemarks WHON.Z.Guide-value Standardslines

Vol. 1

gama-HCH (lindane)Mg/M33 4.3.7.4

paraquat Mg/M310 value set in case of4.3.4.4improper use of paraquatin catchment

pentachiorophenolMg/M310

tetrachloroetheneMg/M310C

trichioroethenemg/rn330

2,4,6-trichlorophenol Mg/M3lOG, d

tentative guideline valuee

tentative guideline value*

odour threshold concen-tration is 0.1 Mg/M3

4.3.7.6

4.3.7.2

4.3.7.2

4.3.7.6

trihalomethanes nosee chloroform 4.3.4.64.3.7.8guide-linevalueset

Parameters of possible health significance not in the table are discussed in Section 4.3.b Mg/M3= g/l parts per billion.

These guideline values were computed by WHO from a conservative hypothetical mathematical model which can-not be experimentally verified and values should therefore be interpreted in the light of the uncertainties involvedwhich may amount to two orders of magnitude.d May be detectable by taste and odour at lower. concentrations.

When the available carcinogenicity data did not support a guideline value, but the compounds were consideredto be of importance in drinking-water and guidance was considered essential, a tentative guideline value was set onthe basis of the available health-related data.

Table 4. Aesthetic QualityGuideline values Document

Constituent Referenceor Unit'Highest Undesirable effect thatWHOcharacteristic Desir-Excessivemay be producedGuide-

able lines

aluminium g/m30.050.2

chloride g/m3100250

Vol. 1

discolouration and depos-4.4.3.1its; possible corrosionassociation; special pre-cautions required for renaldialysis

corrosion, taste threshold4.4.3.2between 200 and 300 g/rn3

11


Table 4. Aesthetic Quality —continuedGuideline values Document

Constituent Referenceor UniteHighest Undesirable effect thatWHOcharacteristic Desir-Excessivemay be producedGuide-

able linesVol. 1

chlorobenzenes andno guideline these compounds can4.3.7.5 &chlorophenols value set affect taste and odour4.3.7.6

colour true530discolouration and trouble4.4.3.3colour with chlorinationunits(TCU)b

g/m3

0.051.0astringent taste, discol-4.4.3.4ouration and corrosion ofpipes, and utensils

g/m3

80200excessive scale forma-4.4.3.5(as tion, electric element burn-CaCO3) out

not detectabletaste and odour 4.4.3.6by consumer

g/m3

0.11.0taste, turbidity, discolour-4.4.3.7ation, deposits, growth ofiron bacteria

g/m3

0.050.5taste, turbidity, discolour-4.4.3.8ation, deposits in pipes

7.4 to 8.5 7.0 to 8.5 corrosionandscale,4.43.10unsatisfactory disinfection

g/m3

100200taste 4.4.3.11

g/m3

5001 000taste 4.4.3.12

g/m 350400corrosion, laxative effect4.4.3.13when magnesium present

---inoffensivetomost4.4.3.14consumers

copper

hardness

hydrogen sulphide

iron

manganese

pH range

sodium

solids(total dissolved)

sulphate

taste and odour

temperature -C C no guideline values set4.4.3.16

turbidity nephelo- 15discolouration; preferably4.4.3.15metric less than 1 NTU for dis-turbi- infection efficiencydityunits(NTU)

zinc g/m355taste, discolouration,4.4.3.17deposits

g/m3 mg/I ppm. Iparts per million).b True colour is the colour of the water from which the turbidity has been removed. It is measured by the platinum-

cobalt standard method."° Cool water is generally more palatable. Low water temperature tends to decrease the efficiency of water treatment

processes, including disinfection. High water temperature encourages growth of nuisance organisms and intensifiestaste, odour, colour and corrosion problems.

12

1. INTRODUCTION

Table 5. Radioactive Constituents

Constituent

gross alpha activity

gross beta activity

DocumentReference

Remarks WHOGuidelinesvol. i

0.1 0(a) if the levels are exceeded moreChapter 5detailed radionuclide analysismay be necessary

1 (b) exceeding the levels does notimply that the water is unsuit-able for human consumption

Bq/l

Bq/l

Guide-Unitline

value

'Becquerel (Bq) is a unit of activity of an amount of radionuclide; 1 becquerel is equivalent to 1 spontaneous nucleartransformation per second and corresponds to approximately 27 picocuries. Water supply authorities are not expectedto sample and test for radioactivity in their drinking water, because a national service for radiation protection isprovided by the National Radiation Laboratory of the Department of Health.

NOTE: EXCEEDING THE GUIDELINE VALUE DOES NOT IN ITSELF IMPLY THAT THE WATER IS UNSUITABLEFOR CONSUMPTION.

1.8 Application of the Drinking-Water Standards for New Zealand

1.8.1 Laws, regulations and standards

In New Zealand, local authorities are enabled by section 379 of theLocal Government Act 1974 to construct or purchase any waterworksafor the supply of pure water and are the principal water supply authorities.

The Health Act 1956 and associated regulations establish the Depart-ment of Health as the surveillance agency for water supply authorities.

Section 60 of the Health Act makes it an offence for any person topollute the water supply of a local authority.

Section 62 enables the medical officer of health to require the cessationof supply of water from a polluted source. Section 63 enables the Direc-tor General of Health to cause the prevention of the use of water froma polluted source at the local authority's expense if there is non-com-pliance with the provisions of section 62.

Under the provisions of the Water Supplies Protection Regulations1961 a local authority providing a water supply has a duty to complywith and enforce the regulations and in particular shall not permit waterother than wholesome drinking water to be present in the water mains.

Under the Health Act, a local authority may be required to provide,alter or extend waterworks. Section 23 of the Health Act 1956 makes itthe duty of local authorities to ensure that conditions likely to be injuriousto health within their districts are rectified. Hence local authorities must

a "Waterworks" includes all rivers, streams, lakes, waters, and underground waters, andall rights appertaining thereto, and all land, watersheds, catchment areas, water collectionareas; reservoirs, dams, bores, tanks, and pipes, and all buildings, machinery, and appliancesof every kind, vested in the council or acquired Or constructed or operated by or underthe control of the council under Part XXIII of the Local Government Act 1974, for orrelating to the purpose of water supply whether within or outside the district.

13


ensure that private supplies serving public groups meet the requirementsof these Standards. Water supplies serving motels, motor camps, com-pany towns, work camps and schools fall into this category.

Section 27 (a) of the Health Act 1956 authorises the Minister of Healthto pay subsidies to local authorities for the construction of water sup-plies. The conditions under which subsidies are granted include arequirement for satisfactory design and construction.

The remainder of the cost of construction of waterworks may be pro-vided from revenue and loans raised under the authority of the LocalAuthorities Loans Board. The Local Authorities Loans Act 1956 andregulations require the Department of Health to advise the board whetherproposals for water supply will promote and protect the health of thepublic.

The Department of Health uses the Drinking-Water Standards for NewZealand as the basis for surveillance of the design, construction and oper-ation of waterworks by water supply authorities, for the purpose of sup-plying pure water, under the provisions of the Local Government Act1974 and for the purpose of ensuring the delivery of wholesome waterto consumers under the provisions of the Water Supplies ProtectionRegulations 1961.

The Department of Health evaluates the degree of compliance withthe Drinking-Water Standards for New Zealand by the water supplyauthorities at 5-yearly intervals for the Board of Health. The evaluationsform part of the publication "Grading of Public Water Supplies in NewZealand".' Water supply authorities should monitor their waterworks,using these standards as the basis for reaching compliance with the lawand regulations, which promote the supply of pure and wholesome water.

1.8.2 Compliance and surveillance

Surveillance of drinking-water quality can be defined as "the contin-uous and vigilant public health assessment and overview of the safetyand acceptability of drinking-water supplies".

The organisation needed to ensure compliance with drinking-waterquality standards is fully discussed in the WHO publicatidn "Surveil-lance of Drinking-Water Quality".3

The Department of Health uses the Drinking-Water Standards for NewZealand as the basis for assessment of activities which fall within itsresponsibilities for the surveillance of drinking-water quality.

Included iii the activities are:(a)approval of new sources;(b)watershed protection;(c)approval of the construction and operating procedures of water-

works, including:(i)disinfection at the plant and of the distribution system after

repair or interruption of supply(ii)periodic flushing programmes and cleaning of water storage

facilities

14

1. INTRODUCTION

(iii)certification of operators(iv)regulation of chemical substances used in water treatment(v)cross connection control, back-flow prevention and leak

detection control programmes(ci) sanitary surveys;(e) monitoring programmes, including provision for central and regional

analytical laboratory services;(j) development of regulations, bylaws and codes of practice for

plumbing;41.8.2.1 Source of water

Selection of source. In selecting a source of drinking-water, a numberof factors may influence the health of consumers. In particular, attentionmust be given to likely future developments that may influence the con-tinued suitability of the source chosen. Important considerations include:

(a) Quantity (source capacity): Is the quantity of water available at thesource sufficient to meet continuing water demands, taking into accountdaily and seasonal variations, and projected growth in the size of thecommunity being served? Operation of treatment plants beyond designcapacity may lead to deterioration in the quality of water supplied.Periodic shortages may force users to alternative, less safe sources.

(b)Quality: Is the raw water quality such that, with appropriate treat-ment, water can be supplied that consistently meets or exceeds the qualityspecified in the drinking-water standards? Sufficient samples should betaken to determine the range of turbidity and bacteriological contami-nation that can be expected.

(c)Protection: Can the watershed be protected from pollution fromhuman excreta, from industrial discharges and from agricultural run-off?

(d)Feasibility: Is the source available at reasonable cost (both inabsolute terms and in comparison with possible alternative sources ofsupply)?

(e)Operator competence: Will the raw water treatment be adequateand reliable under locally prevailing conditions?

Potential new sources should be examined in the field and physical,bacteriological and chemical analyses should be carried out for a suitableperiod (e.g., covering seasonal variations) prior to final selection of thesource. Such information is essential in order to define appropriate watertreatment requirements and necessary pollution control measures to pro-tect raw water sources.5

When alternative water sources are under consideration, it is prefer-able to choose the alternative requiring minimal treatment, other thingsbeing equal; in the case of small undertakings, provision of water fromprotected wells or springs of good quality is often preferable to treatmentof surface water.6

Safeguarding purity of supplies. The guidelines values given in thesestandards for potentially hazardous substances in drinking-water havebeen set as low as possible, with the object of discouraging the deteriora-tion, directly or indirectly, of drinking-water quality.

15


Although water which contains substances at concentrations lower thanthe guideline values specified here is acceptable for lifelong consumption,the establishment of a guideline value should not be regarded as implyingthat the quality of drinking-water may be degraded to the recommendedlevel.

Prevention of contamination. Because water from ground water sourcesis sometimes not chlorinated, there is a particular need for protection ofthe sanitary quality of the water from such sources in order to ensurethat the water will continue to meet the guideline values for micro-biological quality. In particular, sources should be protected from con-tamination from septic tanks, sewers, cesspools, sullage water and floodingor by users.'.'

Maintaining adequate residual chlorine levels in the distribution systemis the most reliable indicator of protection against contamination throughcross-connections, back siphonage, leaks, etc. Interruptions of supply todistribution systems often result in contamination of drinking-water sup-plied to the consumer and a positive mains pressure should be main-tained at all times.

1.8.2.2 Sanitary surveysWhile drinking-water standards provide authoritative criteria con-

cerning the acceptability of water for human consumption, the prescrip-tion of standards in no way obviates the need for sanitary surveys.

The sanitary survey is an on-site inspection and evaluation by aqualified person of all the conditions, devices and practices in the watersupply system which pose, or may pose, a danger to the health and well -being of the water consumer. In 1976, a WHO Monograph provided anin-depth description of the requirements for sanitary surveys, includingguidelines for their conduct.3

No bacteriological or chemical analysis of samples, however carefullyit is made, is a substitute for a complete knowledge of conditions at thesource and within the distribution system, of the adequacy of treatmentand of the performance of the operators. Samples are a minute fractionof the whole, represent a single point in time, and .are reported after theevent. Contamination is often random and intermittent and may not berevealed by occasional sampling.

Sanitary surveys should be undertaken on a regular basis by the per-sonnel of the water supply authority as well as by personnel of theDepartment of Health. In addition, sanitary surveys should be conducted:

(a) when new sources of water are being developed;(b) when laboratory analyses indicate a potential hazard to health;(c) when an outbreak of disease, which could be waterborne, occurs in

or near the area served by the water supply system;(ci) when any significant change or event occurs that could affect water

quality (e.g., drought, changes in land use, agricultural patterns, newindustrial construction on the watershed).

16

I. INTRODUCTION

Sanitary surveys should be conducted with sufficient frequency to beuseful in interpreting trends or sudden significant changes in the qualityof drinking-water as determined by physical, microbiological and chemicalmonitoring.

Although smaller systems often present propoitionately greater hazards,the larger systems should be inspected more frequently because of thelarger population at risk and greater cost-effectiveness of surveillance.The smaller systems should also be surveyed, but with realistic frequencydepending on the quality of the source water.

1.8.2.3 Monitoring responsibilitiesWater supply authorities are responsible for monitoringa the quality

of their supplies for those parameters requiring relatively regular andfrequent determination in order to assure the delivery of safe and accept-able water.

In particular, all water supply authorities should arrange for:(a) the bacteriological testing of their supplies;(b) sufficient chemical and physical testing to control their water treat-

ment processes;(c) the testing of their supplies for biological, chemical and physical

parameters which are likely to affect their particular water supplies.Establishing water quality testing laboratories should be considered as

an item within the functions of the larger local authorities responsiblefor the provision of safe drinking-water, which might make their facilitiesavailable to other local authorities.

The Department of Health, as the surveillance agency, arranges for theperiodical chemical testing of all public water supplies, particularly forthose substances which are likely to be present and which require sophis-ticated testing procedures for their identification and measurement. Thedepartment also conducts overall bacteriological testing of supplies forsurveillance purposes.

The department, using the analytical services of the Department ofScientific and Industrial Research, provides a comprehensive analysis ofwater samples collected from sources, treatment plants and reticulationsfor all graded and many ungraded water supplies. Each supply is exam-ined at least once every 5 years in a rolling programme. Most, of theinorganic constituents of health significance (Table 2) are determined inall supplies. The likely occurrence of organic health related constituents(Table 3) and the few remaining inorganic health related constituents iskept under review and occasional surveys are undertaken to confirmassessments of likely occurrence. Accordingly, the Department of Healtheffectively accepts responsibility for such monitoring as is required for

"'Monitoring" is defined as: "The programmed process of sampling, measurement andsubsequent recording or signalling or both, of various water characteristics, often with theaim of assessing conformity to specified objectives", Draft International Standard ISO/DIS6107/2 Water Quality—Vocabulary—Part 2 (1980).

17


the inorganic and organic constituents of health significance and watersupply authorities will not usually need to make separate arrangementsfor determination of these constituents.

The comprehensive analyses provided by the Department of Healthalso give an indication of constituents in Table 4 likely to cause problemsand accordingly assist water supply authorities to select parameters whichshould be included in their monitoring programmes.

The Department of Health also accepts a monitoring function for bac-teriological and general chemical and physical testing of supplies wherelocal authorities are unable to provide a satisfactory service.

The National Radiation Laboratory of the Department of Health con-ducts the surveillance of the radiological quality of surface and ground-waters in New Zealand. In normal circumstances this system makesradiological testing of individual water supplies unnecessary. In the eventof any special circumstances arising, the National Radiation Laboratorywould arrange special surveillance systems.

1.8.2.4 Priorities for monitoringBecause drinking-water can act as a vehicle for the transmission of a

number of serious infective diseases, the bacteriological quality of wateris of paramount importance and monitoring of indicator bacteria suchas coliform and faecal coliform organisms should be given the highestpriority. With conventional bacteriological testing, results are not avail-able for at least 24 hours, during which time the community may be atrisk. Measurement of free chlorine residual, which is quick and easy toperform, should also be undertaken frequently where a free chlorineresidual is maintained throughout the distribution system. This permitsimmediate corrective action in case of a malfunction in the treatmentprocess or if easily oxidizable material enters the distribution system.

Sanitary surveys can give valuable indications of the relative prioritiesthat should be accorded for monitoring of chemical constituents. Aknowledge of industrial and agricultural activities conducted in thewatershed will often suggest which chemical substances are likely to occurin the drinking-water. The analytical procedures necessary to monitorfor these substances, especially the organic compounds, may require theuse of relatively sophisticated and expensive equipment which is rarelyavailable. In such cases, calculation of the actual quantities of wasteeffluents, for example, in conjunction with flow rates in water courses,may give an approximate indication of likely concentrations in drinking-water. If such calculations suggest that the probable concentrationsapproximate or exceed the guideline values, arrangements ought to bemade for samples to be analysed at a laboratory possessing the requiredequipment; however, if the calculations suggest that likely concentrationsin drinking-water will be only a small fraction of the guideline values,the relative priority for monitoring can be assigned accordingly.

Taste, odour, colour and turbidity of water can be assessed relativelyeasily and ought to be accorded fairly high priority since they can give

18

I. INTRODUCTION

useful indications, especially of sudden changes brought about by ruptureof pipes, etc.

Simple observations are particularly useful for immediate on-siteassessments of these characteristics, especially when personnel are famil-iar with the normal range of these characteristics for the supply. Colouris readily discernible by most consumers in a glass of water at a levelof 15 True Colour Units, and a level of 5 TCUs will be apparent in largevolumes of water. Few people can detect a colour level of 3 TCUs. Ifturbidity is less than 1 NTU (to give a high level of assurance of theeffectiveness of chlorination) there should be no cloudiness apparent inabout a 1 m depth of water. If cloudiness is apparent in water in a clean,unscratched 2 litre jar, the turbidity probably exceeds 3 units. The shapeof stones and other major features would be just discernible in pools(3-4 m deep) at about 1 NTU when viewed through a glass to eliminatesurface reflection.

Pleasing aesthetic qualities serve to discourage use of alternative sources(which may be less safe) and individual home water treatment devicesthat may produce aesthetically pleasing water, but have poor quality con-trol, where health-related parameters are concerned.

1.8.2.5 PersonnelThe adoption of drinking-water standards implies the need to provide

suitably qualified and experienced staff to undertake the production andmonitoring of drinking water of satisfactory quality. It is also preferablethat the water supply be managed by a technical director who is a profes-sional engineer with water works experience and that other staff be care-fully selected and trained.(a) Water treatment plant operators

Facilities for the training and certification of water treatment plantoperators and supervisors are provided by the Ministry of Works andDevelopment at its Water Treatment Centre. The centre also providesa wide range of services to the water industry including advice and ana-lytical services. These resources are available to all water supply authori-ties and to private industry. Full details are available through the PublicHealth Engineering Section, Ministry of Works and Development.(b) Servicemen and field personnel

At the present time (1984), there is no formal training facility for fieldpersonnel such as servicemen, overseers and others involved in theinstallation, repair and maintenance of water supply works. This defi-ciency has been partially filled by the publishing of the "Instruction andTraining Manual for Waterworks Overseers, Foremen and Service-men", 9 by the Local Government Training Board in association with theWater Supply Engineers Committee (N.Z.). Enquiries should be madeto the Local Government Training Board.

It must be emphasised that care should be exercised in the selectionof employees for work where a risk to the purity of the water is likely

19


to arise. Any employee suffering from diarrhoea or open sores who isemployed on work where there is a risk of the water becoming contam-inated should be removed from such work until he or she has fullyrecovered. These precautions are especially important with untreatedwater supplies.

Employees suffering from diseases that may be transmitted in water,or who might be carriers of such diseases, should not come into contactwith the water during storage, treatment or distribution, or with surfacesthat might convey contamination to the water. The medical history ofeach person should be investigated, with particular attention paid to anyinfection capable of being waterborne. Appropriate laboratory tests shouldfollow, for example, if there has been a past history of typhoid fever orprevious residence in a country where the incidence of enteric disease ishigh.

In the event of an epidemic or threatened outbreak, special precau-tions may be needed to ensure that drinking-water supplies remain safe.Close liaison between the waterworks' management and the medicalofficer of health is essential and close medical surveillance of waterworks'employees is particularly important at such times.

1.8.3 Remedial actionThe major purpose of monitoring activities is the detection of defi-

ciencies (and potential deficiencies) in the drinking-water supply as soonas possible, preferably before there is any impact on the health of con-sumers. It is axiomatic that deficiencies should be corrected with theleast possible delay.

This implies rigorous, vigilant examination andanalysis of informa-tion gathered in monitoring activities. When potential risks are discov-ered, action must follow. However, it is self-evident that not all potentialrisks are equally serious. For example, the failure of a chlorination plantduring a typhoid outbreak would require immediate correction; provi-sion of a standby chlorinator for a small system drawing water from deepwells might be accorded much lower priority.

Once a potentially hazardous situation has been recognised, the prob-ability that it will occur, the potential consequences and the availabilityof alternative sources, costs, etc., must be considered in order to makea decision about the acceptability of risk.

Depending upon the nature of the deficiency, a number of alternativemeasures may be available to the surveillance agency. Some of thesemay be temporary, short-term measures intended to provide a measureof protection in an emergency situation, such as "boil water" orders.Such measures must not be allowed to become a substitute for initiatingmore satisfactory solutions to the problem in the longer term.

Evidence of faecal contamination of drinking-water supplies mustalways be acted upon immediately. However, a decision to close thesupply carries an obligation to provide an alternative, safe supply.

20

1. INTRODUCTION

Instructing consumers to boil water, initiating super-chlorination andundertaking immediate corrective measures may be preferable. Drink-ing-water standards are intended to ensure that the consumer enjoys safepotable water, not to shut down deficient water supplies.

1.8.4 Special considerations for small rural water supplieiThere are particular problems associated with ensuring that small rural

systems comply with drinking-water standards. These can arise, forexample, because of the distance and lack of good transportion to thenearest laboratory; bacteriological monitoring is a special problem. Insuch cases, emphasis should be placed on:

(a) selection of adequate, safe sources, preferably those which do notrequire treatment;

(b) frequent, regular sanitary surveys by adequately trained localoperators;

(c) testing to ensure bacteriological quality of the source;(ci) testing chlorine residuals (in chlorinated systems): this is a quick

and easy test to perform and is a good indicator of the bacteriologicalintegrity of waterworks operations;

(e) simplicity of equipment and reliability of operation.

21

2. MICROBIOLOGICAL ASPECTS

2.1 The bacteriological quality of drinking-water2.1.1 Introduction

Any judgment of drinking-water quality involving the use of bacterialguidelines should be based on an appreciation of the precision, validityand appropriateness of sampling procedures. Consideration should alsobe given to the species of waterborne pathogens present, the likely cor-relation between the levels of these pathogens with densities of indicatorbacteria and the capabilities and limitations of water-treatment.

Natural and treated waters vary in microbiological quality. Ideallydrinking-water should not contain any micro-organisms known to bepathogenic. It should also be free from bacteria indicative of pollutionwith excreta. To ensure that a supply of drinking-water satisfies theseguidelines of bacterial quality, it is important that samples should beexamined regularly for indicators of faecal pollution. The primary bac-terial indicator recommended for this purpose is the coliform group oforganisms as a whole. Although as a group they are not exclusively offaecal origin, they are universally present in large numbers in the faecesof man and other warm-blooded animals, thus permitting their detectionafter considerable dilution. The detection of faecal (thermotolerant) col-iform organisms, in particular Escherichia co/i, provides definite evi-dence of faecal pollution.

The methods used to detect and confirm the presence of coliformorganisms are designed to demonstrate one or more of the properties inthe following working definition—which is practical rather thantaxonomic.

The term "coliform organisms" (total coliforms)a refers to any rod-shaped, non-spore forming, Gram-negative bacteria capable of growthin the presence of bile salts or other surface-active agents with similargrowth-inhibiting properties, which are cytochrome oxidase negativeand able to ferment lactose at either 35 or 37°c with production ofacid, gas and aldehyde within 24-48 hours.

Those which have the same, properties at a temperature of 44 or44.5°c are described as faecal '(thermotolerant) coliform organisms.Faecal coliform organisms which ferment both lactose and other suit-able substrates such as mannitol at 44 or 44.5°c with the productionof acid and gas, and which also form indole from tryptophan, areregarded as presumptive E. co/i. Confirmation as E. co/i may be made

° "Total coliforms" are assumed to be equivalent to "presumptive coliforms".'°

22


by demonstration Of a positive result in the methyl red test, by failureto produce acetyl methyl carbinol and failure to utilise citrate as thesole source of carbon.These steps in the detection and confirmation of coliform organisms

should be regarded as parts of a progressive sequence, those needed forany particular sample depending partly on the type of water, partly onthe objective of the examination, and partly on the capability of thelaboratory.

Supplementary indicator organisms, such as faecal streptococci andsulfite-reducing clostridia, may sometimes be useful in determining theorigin of faecal pollution as well as in assessing the efficiency Of watertreatment processes.

2.1.2 Guideline valuesThe values for bacteriological quality given in Table 1 are only a guide

to those required to ensure bacteriologically safe supplies of drinking-water whether piped, unpiped or bottled.2.1.2.1 Piped supplies2.1.2.1.1 Treated water entering the distribution system

Efficient treatment culminating in disinfection should yield water freefrom coliform organisms, however polluted the original raw water mayhave been. In practice, this means that it should not be possible todemonstrate the presence of any coliform organisms in any sample of100 ml. A sample from the water entering distribution which shows anydeviation from this value calls for an immediate investigation into boththe efficacy, of the treatment process and the method of sampling. Whenwater is disinfected, it is important that the residual disinfectant con-centration should be measured regularly and, if possible, recorded con-tinuously. For effective disinfection, it is important that the turbidityshould be as low as possible and preferably less than 1 nephelometricturbidity unit (NTU). In addition, when chlorination is practised, thepH should preferably be less than 8.0 and the contact time greater than30 minutes, resulting in a free chlorine residual of 0.2-0.5 g/m 3. Thehigher residual is desirable for water from unprotected sources.

The objective is to maintain a detectable free chlorine residual at thefurthest end of the reticulation. Where the dosing point is remote fromthe distribution system a free chlorine residual of more than 0.5 g/m3may be necessary. Large supplies may require supplementary chlorinedosing points.

2.1.2.1.2 Untreated water entering the distribution systemThe desirability of disinfecting all supplies of piped drinking-water

before distribution should be considered. Supplies derived from pro-tected sources which are distributed without disinfection should be simi-lar in quality to that of disinfected drinking-water. No water entering a

23


distribution system should be considered satisfactory if coliform organ-isms are detected in any sample of 100 ml. The presence of not morethan 3 coliform organisms per 100 ml may be tolerated in occasionalsamples provided that faecal coliform organisms are absent; the sourcehas been regularly and frequently tested, and sanitary inspection hasshown the catchment area and storage conditions to be satisfactory. Asa further guide, for large supplies it is recommended that throughout anyperiod of 1 year no coliform organisms should be detected in 98 percentof all routine samples—provided that sufficient samples have beenexamined. This requirement is not applicable to small supplies, but inthe event of an unsatisfactory coliform result, the desirability of increas-ing the frequency of sampling should also be considered. In additioncoliform organisms should not be detected in any two consecutive rou-tine samples. Consideration should be given to the use of time intervalsof less than 1 year when assessing results from these examinations.

In the event of persistent failures, the area should be surveyed to locatethe source of pollution. Whenever the findings of bacteriological exam-ination or of sanitary inspection indicate that the source may be subjectto pollution, no matter how remote or infrequent this may be, disinfec-tion should be started as a precautionary measure.

2.1.2.1.3 Water in the distribution systemWater that is of potable quality when it enters the distribution system

may undergo deterioration before it reaches the consumer. Just as muchdeterioration may occur in the distribution system of a chlorinated sup-ply in which the residual has been dissipated as may occur in that of anon-disinfected supply, so that in this respect the two are similar. Waterin the distribution system may become contaminated through cross-con-nections, back-siphonage, leaking service connections, defective storagetanks and service reservoirs, and damaged hydrants, during main-layingand repair, or through inexpert repairs to domestic plumbing systems.Such contamination may be at least as dangerous as the distribution ofinsufficiently treated water. Ideally, all samples taken from the distri-bution system, including those from consumers' premises, should be freefrom coliform organisms. In practice, this is not always attainable andfor this reason the following guidelines are recommended for water inthe distribution system:

—Faecal (thermotolerant) coliforms should not be detectable in anysample of 100 ml.

—No sample of 100 ml should contain more than 3 coliform organ-isms. If any coliform organisms are found, the minimum actionrequired is resampling immediately, and always within 3 days.

—As a further guide for large supplies, coliform organisms should notbe detectable in 95 percent of routine samples examined throughoutany period of 1 year. For small supplies, this compliance require-ment is not applicable, but, in the event of an unsatisfactory coli-form result, the desirability of increasing the frequency of samplingshould be considered.

24


—Coliform organisms should not be detectable in any 2 consecutiveroutine samples of 100 ml collected from the same sampling point.

The repeated demonstration of coliform organisms, or their appear-ance in large numbers, suggests that contamination of the water is occur-ring and remedial action, especially in relation to the chlorine residual,should be taken at once. The actual measures will vary with circum-stances but the minimum action must be resampling. The problem canbe considered to be resolved only if a cause is found and eliminated orif a series of samples shows that the pollution was temporary.

No amount of routine bacteriological testing can be expected to detectthe chance ingress of pollution caused by back-siphonage or cross-con-nections. The enforcement of the Water Supplies Protection Regulations1961 should enable back-siphonage and cross-connections to becontrolled.

A disinfectant residual is capable of combating limited entry of pol-lution. If it disappears unexpectedly, this indicates that material, whichcould be faecal in origin, has gained access to the water supply. Thedisappearance of a chlorine residual represents a loss of protection, andshould result in immediate sanitary inspection and bacteriological exam-ination. Whenever there is doubt about the nature of the pollution, espe-cially when coliform organisms only are found, then further examinationfor supplementary indicator organisms should follow.

2.1.2.2 Unpiped water suppliesWhere it is impracticable to supply water to consumers through a piped

distribution network and where untreated sources, such as wells, bore-holes and springs—which may not be naturally pure—must be used, theguidelines recommended for piped supplies may not be attainable. Insuch circumstances, disinfection—although desirable—is not alwayspracticable, and considerable reliance must be placed on sanitary inspec-tion and not exclusively on the results of bacteriological examination.Everything possible should be done to prevent pollution of the water;Obvious sources of contamination should be removed from the immed-iate catchment area, special attention being given to the safe disposal ofexcrement .7-

Bacteriologically, the objective should be to reduce the coliform countto less than 10 per 100 ml but more importantly, to ensure the absenceof faecal coliform organisms. If these organisms are repeatedly found,or if sanitary inspection reveals obvious sources of pollution which can-not be avoided, then an alternative source of drinking-water should besought. Greater use should be made of protected groundwater sourcesand rainwater catchments as these are more likely to meet the guidelinesfor potable water quality.

All sources of drinking-water, including those used for private sup-plies, come within the jurisdiction of local authorities and should be ofpotable quality. The results of bacteriological tests and those of sanitarysurveys should therefore be used to encourage improvement. Partial

25


treatment may be necessary to remove turbidity even when coliformcounts are low; and other quality criteria may dictate the need for treat-ment processes.

2.1.2.3 Drinking-water in containersIt is not intended that the criteria should be used for the quality of

commercially bottled water, which should comply with the requirementsof the Food and Drug Regulations 1973. The standard is for the qualityof water stored in containers for emergency and other purposes.

Water in containers must be at least as good in bacterial quality aspotable water and thus contain no coliform organisms. The source usedfor bottled water should be free from faecal pollution and the fillingprocess, subsequent transit, and storage should be hygienic.

2.1.2.4 Emergency supplies of drinking-waterDuring emergencies it may be necessary to modify the treatment of

existing sources or to use alternative sources of water." It may be neces-sary to increase the rate of disinfection or to re-chlorinate during dis-tribution. If possible the distribution system should be kept undercontinuous pressure to avoid the entry of contamination which mayspread disease.

If quality cannot be maintained consumers should be advised to boilthe water for at least 3 minutes. 12 Any tankers used should be disinfectedor steam cleaned before use and sufficient chlorine added to ensure thata free residual of at least 0.5 g/m 3 is available at the delivery point.' 5 Ifswimming pool disinfectants have to be resorted to in emergencies pref-erence should be given to sodium hypochlorite solution or calciumhypochlorite powder, granules or tablets not containing çyanuric acid.Some proprietary water disinfection tablets for campers and travellersdo contain cyanuric acid and may be used for disinfection of individualdomestic supplies.

2.1.3 Frequency of sampling

Examination of drinking-water should be both frequent and regular,sampling must be performed carefully, and bacteriological results shouldcomply with these standards.

A new source of water supply should be monitored more frequentlythan it would be under normal circumstances so that variations in qualitycan be observed under a variety of conditions.

2.1.3.1 Treated water entering the distribution systemAny source of water which requires treatment—including disinfec-

tion—should be examined frequently for coliform organisms, turbidityand pH at the point at which the water enters the distribution system

26


as the threat of pollution from the source is continuous and the treatmentbarrier should not be penetrated. In addition, the residual disinfectantconcentration should be measured frequently and preferably recordedcontinuously. Any deterioration in quality or protection thus revealedshould result in an immediate investigation without awaiting the out-come of accompanying bacteriological tests.

2.1.3.2 Water in the distribution systemIn piped water supplies, contamination of the distribution system

increases in importance with the length of pipe work and the numberof plumbing systems attached to it. Although it is desirable to take sam-ples at least weekly, this may not be possible with small systems.Decisions on sampling frequencies should be taken in conjunction withthe Department of Health. The following minimum sampling frequen-cies are recommended:

Population served

less than 5 000

5 000 to 20000

20 000 to 50 000

Maximum intervalbetween successivesamples

more than 50000sample atdays/week

Recommended sampling frequency forcoliform analysis

—one sample per month

—one sample per 5 000 population permonth

—one sample per 5 000 population permonth

least 4—one sample per 5 000 population permonth

1 month

2 weeks

4 days

A proportion of the samples should be taken at certain fixed pointssuch as pumping stations and storage tanks, as well as from sites whereprevious sampling has revealed problems; other samples should be takenrandomly throughout the distribution system including multiple occu-pancy buildings such as hospitals, schools, public buildings, apartmentblocks, hotels, factories and other locations where there is greater pos-sibility of contamination through cross-connections and back-siphonage.The frequencies given above should be regarded as the minimum neces-sary, the overall aim being to increase the sampling programme, espe-cially at times of epidemic, flooding or during emergency operations andfollowing interruption of supplies as well as repair and renewal work.

2.1.3.3 Untreated water and unpiped suppliesThe quality of water will vary with both season and proximity to

sources of pollution. The frequency of sampling for bacteriological exam-ination of a particular water should therefore be established by localauthorities and it should reflect local circumstances, including the popu-lation served and the results of sanitary surveys.

27


2.1.4 Collection, storage, and transport of water samplesfor bacteriological examination

Care must be taken to ensure that samples are representative of thewater being examined, and that no accidental contamination occursduring sampling. Sample collectors should therefore be made aware ofthe responsible nature of their work and be adequately trained.

Most samples will be taken from taps in treatment works, storage tanks,houses or from public standpipes. When sampling the distribution sys-tem, both domestic and communal taps, including public fountains, mustbe selected with care. Public health and water supply authorities shouldselect sampling points according to an agreed programme. The taps cho-sen must be clean and should be supplied with water direct from thepublic main. Additional samples may be needed to monitor storage tankssupplying high-rise and multiple occupancy buildings. Samples shouldnot be taken from taps which leak between the spindle and gland aswater from, the outside of the tap may contaminate the sample. Externalfittings such as filters, rubber or plastic nozzles and other anti-splashdevices should be removed, and the water run to waste for at least 1minute to ensure that stagnant water is flushed from the pipes beforethe sample is taken. Flaming of the tap before the sample is taken shouldbe considered an optional procedure. To reduce some of the problemsinherent in sampling from domestic taps, water supply authorities shouldconsider the installation of sampling taps at strategic points in distri-bution systems.

For bacteriological examination, samples should be collected in clean,sterile, glass or autoclavable plastic bottles containing 0.1 ml of a 1.8percent solution of sodium thiosulfatea per 100 ml of sample bottlecapacity to neutralise any residual disinfectant. This should neutralise atleast 5 g/m 3 of available chlorine and will be suitable for routine sam-pling. In special situations where the chlorine residual may be greater,as for example in emergencies, additional thiosulfatè is required. Sam-ples should be kept cool and in the dark, preferably at 4-10°c, and trans-ported to the laboratory as quickly as possible for examination, ideallywithin 6 hours of collection, but never more than 24 hours later. Wheremore than 6 hours delay before examination is anticipated samples shouldbe maintained at 4°c or less but notfrozen.

2.1.5 Techniques for the detection of coliform organismsTwo basic procedures are used for the detection and enumeration of

coliform organisms in water: (a) the multiple tube method in whichmeasured volumes of water are added to sets of tubes containing a suit-able liquid medium; (b) the membrane filtration technique in whichmeasured volumes of the sample are filtered through a membrane fil-ter. 11 Both methods have advantages and disadvantages and are sub-ject to statistical variability. The two methods do not give strictly

18 g of Na, SO 4. SH 2O per litre of water.

28


comparable results—one reason being that counts on membrane filtersdo not give a direct indication of gas production from lactose—but inpractice they do yield comparable information.

2.1.5.1 Multiple tube methodIn this method, the examination starts with the presumptive coliform

test, in which measured volumes of the sample, or one or more dilutionsof it, are inoculated into a series of bottles or tubes containing a suitableliquid differential medium containing lactose. After incubation at 35-37°Cfor an appropriate time, the tubes are examined for acid and/or gas pro-duction. The test is called presumptive, because the positive reactionobserved may be caused by some other organism or combination oforganisms. The presumption that the positive reaction is caused by col-iform organisms should therefore be confirmed by additional tests withfurther differential media. The occurrence of false-positive reactionsdepends partly on the bacteria in the sample of water and partly on themedium used.

By inoculation of appropriate volumes of water into a suitable numberof tubes, a statistical estimate of the most probable number of coliformorganisms in a given volume of water can be obtained—based on theassumption that, on incubation, each tube which received one or moreviable coliform organisms will show growth. Provided negative resultsoccur in some tubes, the most probable number (MPN) of coliformorganisms in the original sample may be estimated from the number oftubes giving a positive reaction. Tables of statistical probability are nor-mally used for this purpose, and those given in Standard Methods forthe Examination of Water and Wastewater, 14 show the most probablenumber of coliform organisms in 100 ml of the original sample for vari-ous combinations of positive and negative reactions, together with their95 percent confidence limits.

The MPN procedure is a multiple-tube dilution method using nutrient-rich media which is applicable to waters of all types. The equipmentrequired is relatively cheap and unspecialised. Positive reactions are usu-ally easy to read and are interpreted readily. However, .the technique canonly provide an estimate of the number of bacteria present in any sampleand this estimate is subject to considerable inherent error, though thatdoes not detract from the ability of the test to detect pollution. Becauseliquid media are used, sub-cultures must be made on solid media toobtain pure culture isolates before further differentiation of coliform orother organisms is undertaken.

2.1.5.2 Membrane-filtration techniqueWith this method, the number of coliform organisms in water is deter-

mined by filtering a measured volume of the sample, or an appropriatedilution of it, through a membrane filter, usually made of cellulose esters.Bacteria in the sample are retained on or near the surface of the mem-brane, which is then incubated face upwards on a suitable selective

20


medium containing lactose. All acid- or aldehyde-producing colonies thatdevelop on the membrane are counted either as presumptive coliformorganisms or as faecal coliform organisms, depending on the temperatureof incubation. Since it is not possible to detect gas production on mem-branes, it is assumed that all colonies that produce acid or aldehyde alsoproduce gas. However, the tests used for subsequent confirmation of thesecolonies would demonstrate the formation of gas as would a negativecytochrome-oxidase test. Colonies are counted and the results expressedin terms of colony-forming units present in 100 ml of original sample.Although the membrane filtration method yields direct counts, theyshould be regarded as estimates since the examination of replicate sub-samples of water could not be expected to give the same numerical results.These could be within a statistically calculated range which is generallywithin ± 25 percent of the observed number of colonies, except for lowcounts, where it is greater.

It is usual to incubate two membranes for each sample, one at 35-37°cand the other at 44-44.5°c. The confirmation procedure is simpler thanin the multiple-tube method as the elevated temperature of incubationprovides a direct estimate of the number of faecal coliform organismsmore quickly, thus permitting earlier remedial action. However, certainwater samples may cause problems. Although the technique can be usedfor the examination of all waters, high turbidity will cause blocking ofthe membrane pores before sufficient water can be filtered. The mem-brane filtration method is also unsuitable for use with waters that containonly small numbers of coliform organisms in the presence of many otherorganisms, as growth of the latter may cover the whole membrane andthus interfere with, or suppress, growth of the coliform organisms. Thetechnique may be modified for the recovery of organisms stressed ordamaged, for example by exposure to heavy metals or disinfectants. Pre-incubation at lower temperatures or on less selective media may encour-age recovery and initiation of growth before completion of the test onmore selective media. Basic advantages of the membrane filter techniqueare rapid test results, savings in materials, less incubator space per test,and the reduction in test-processing time compared to the multiple-tubeprocedure. In some instances, the cost of membranes may limit localuse of this technique for the routine monitoring of water supplies.

2.1.5.3 Rapid methods for the detection of coliform organisms

Rapid methods for assessment of the hygienic quality of water shouldbe within the capability of most water supply laboratories for use in theevent of treatment plant failures, breaks in the integrity of the distri-bution system, or in disasters. One of these methods needs only rela-tively simple equipment and the results should be available within 8hours. One such application for faecal coliform organisms has beendescribed. This membrane filtration procedure uses a lightly bufferedlactose/mannitol medium with incubation for 7 hours at 41.5°c.15

30


2.1.5.4 Plate counts 16

Plate counts (colony counts) on nutrient agar at 35-37C or gelatin at20°c are sometimes used in the bacteriological examination of water.The plate count alone is of little value in detecting the access of faecalpollution, since organisms of all types capable of growing at these tem-peratures will be counted. A series of plate counts from a source suchas a deep well or a spring may be of considerable value—a sudden increasein the plate count from such a source may give the earliest indicationof the access of pollution. Plate counts frequently repeated from a seriesof points in a treatment plant are of considerable value in the controlof treatment.

2.2 The virological quality of drinking-water

Drinking-water should be free from any viruses infectious to man.This objective may be achieved (a) by the use of water from a sourcewhich is free from wastewater and is protected from faecal contamina-tion; or (b) by the adequate treatment of a water source that is subjectto faecal pollution.

Adequacy of treatment cannot be assessed in an absolute sense becauseneither the available monitoring techniques nor the epidemiologicalevaluation is sufficiently sensitive to ensure the absence of viruses. How-ever, it is considered at present that contaminated source water may beregarded as adequately treated when the following conditions are met:

—a turbidity of 1 NTU or less is achieved;—disinfection of the water with at least 0.5 g/m3 of free residual chlor-

ine after a contact period of at least 30 minutes at a pH below 8.0.The turbidity condition must be fulfilled prior to disinfection if ade-

quate treatment is to be achieved. Disinfection other than by chlorina-tion may be applied provided the efficacy is at least equal to that ofchlorination as described above. Ozone has been shown to be an effectiveviral disinfectant, for clean water, where residuals of 0.2-0.4 g/m 3 aremaintained for 4 minutes. Ozone has advantages over chlorine for treat-ing water containing ammonia, but it is not possible to maintain a resid-ual in the distribution system.'7

2.3 Nature of the guideline values

There are some differences between enterovirus and coliform strainswith regard to natural survival and perhaps resistance to chlorination,but these are biological variations that are more clearly demonstrated inthe laboratory than in the application of conventional water treatmentprocesses. Field investigations on virus occurrence in drinking-water andrelated total coliform measurements still support the continued routineuse of coliform limits for monitoring the bacterial and viral quality ofpublic water supplies. When chlorination is practised it has been dem-onstrated that virus-free water can be obtained from faecally polluted

31


source waters when the concentration of free residual chlorine is at least0.5 g/m 3 for a minimum contact period of 30 minutes at a pH below 8.0and turbidity equal to or less that 1 NTU. It is also desirable to maintaina detectable free chlorine residual in the distribution system to reducethe risk of microbial regrowth and to provide an indication of the absenceof post-treatment contamination.

Further information about the nature of the guideline values, moni-toring, remedial measures and cost benefit is given in Vol. 1 of the WHOGuidelines for Drinking- Water Quality.

2.4 Test Methods

The test methods given in paragraphs 2.1.5 to 2.1.5.3 should be used.Reference should also be made to the latest edition of "Standard Methodsfor the Examination of Water and Wastewater")4

The tables given in Annex 2 of the WHO Guidelines for Drinking-Water Quality Vol. 1, for determining the Most Probable Number ofParticular Organisms present in 100 ml of water should be ignored andthose included in the latest edition of "Standard Methods" 4 should beused.

32

3. BIOLOGICAL ASPECTS3.1 Protozoa

Species of Protozoa known to have been transmitted by the ingestionof contaminated drinking-water include Entamoeba histolytica (cause ofamebiasis), Giardia spp. and, rarely, Balantidium coli. These organismscan be introduced into a water supply through human or, in someinstances, animal faecal contamination.

3.1.1 Piped and unpiped suppliesThe organisms are comparatively rarely identified in New Zealand and

in view of the control of human access to water supply catchments andthe degree of treatment of sewage in this country, the organisms are notlikely to be present in drinking-water supplies.

It has been reported that these organisms are more resistant to chlo-rination than bacteria or viruses, but that coagulation followed by sedi-mentation and filtration will remove them.18

Since there is no good indicator for the presence or absence of path-ogenic protozoa drinking-water sources not subject to faecal contami-nation should be used wherever possible.

3.1.2 MonitoringStandard methods are not currently available for the detection of path-

ogenic protozoa in water supplies in the context of a routine monitoringprogramme. Research methods employing cyst concentration by microfiltration and microscopic and/or cultural identification techniques areavailable 14 but are recommended for use only in association with con-current epidemiological studies of either epidemic or endemic situations.However, the methods available at present are inefficient; the concen-tration techniques are not reproducible; the identification of organismsin concentrated samples is difficult, and, at least in the case of Giardiaspp., the viability and origin of detected cysts cannot be determined. Inaddition, no recommendations can be made regarding frequency ofsampling.

3.2 HelminthsThe infective stages of many parasitic roundworms and flatworms can

be transmitted to man through drinking-water. A single mature larva orfertilised egg can cause infection and it is clear that such infective stages

33

DRINKING-WATER STANDARDS FOR NEW ZEALAND•

should be absent from drinking-water. However, the water route is rela-tively unimportant except in the case of Dracunculus medinensis (theguinea worm) and the human schistosomes, which are primarily hazardsof unpiped water supplies. While there are methods for detecting theseparasites they are quite unsuitable for routine monitoring.

These organisms are rare in New Zealand, but are occasionally importedfrom overseas. Because water supplies are well-protected and satisfactorysewage disposal is widespread and effective, the normal precautionsagainst the contamination of drinking-water by faecal matter should beadequate.

3.3 The free-living organisms

The free-living organisms that may occur in water supplies includefungi, algae, free-living protozoa, cladocera, copepods, and macroinver-tebrates such as the nematodes, chironomids and snails.

Free-living organisms present in water supplies may cause adverseeffects to health, aesthesic problems, objectionable odours and taste, andalso can interfere in water treatment. Although organisms, found to infestdistribution systems in temperate climates may not be .associated withknown adverse health effects, it is desirable for aesthetic reasons thattheir appearance at the consumer taps be minimised. The present state-of-the-art does not permit the establishment of guideline values, but itis recommended that, whenever possible, free-living organisms beremoved from drinking-water. Concentrations may be controlled undermost circumstances by protection of sources, reducing or preventing highnutrient levels, use of algicides, adequate water treatment including coag-ulation, sedimentation, filtration, and disinfection, and by protecting andcovering finished water stored in reservoirs.

34

4. CHEMICAL AND PHYSICAL ASPECTS4.1 Introduction

The sophisticated methods now used in analytical chemistry allow fora more specific determination of the many components in drinking-water,especially those in the organic fraction, than was possible a decade ago.

This is particularly important since advances in modern technologyhave resulted in the use and disposal of ever-increasing quantities of bothorganic and inorganic chemicals, with associated hazards to drinking-water.

4.1.1. Nature of the guideline valuesThe Drinking-Water Standards for New Zealand include guideline

values for potentially hazardous constituents in drinking-water as wellas for substances and characteristics that affect the palatability and theappearance of drinking-water.

In comparison with other countries, the nature of the major sourcesof drinking-water in New Zealand ensures that there is less chance ofcontamination of drinking-water by toxic chemical substances. The pre-dominance of protected upland catchments and artesian undergroundsystems as sources make it less likely that pollutants of industrial originwill be present in samples of drinking-water. The remoteness of NewZealand and the absence of land frontiers help to protect natural watersfrom airborne and waterborne wastes. Some of the substances includedin Tables 2, 3 and 4 occur naturally in New Zealand and others arepresent because of their uses in pest control and timber treatment prac-tices or as residues from agricultural and industrial waste disposal sys-tems. They are more likely to be found in samples from sources ofdrinking-water in unprotected catchments and the lower reaches of riversystems. Some bores and wells in shallow unprotected acquifers may alsocontain these substances.

Natural processes in lakes, rivers and the ground reduce the levels inwaters of some of the chemicals and further reduction may result fromnormal water treatment processes.

4.1.2 The health effects of chemical contaminantsThe health risk due to toxic chemicals in drinking-water differs to that

caused by microbiological contaminants. It is very unlikely that any onesubstance could result in an acute health problem except under quiteexceptional circumstances, such as massive contamination of the supply.

35


Moreover, experience shows that the water usually becomes undrinkableafter such incidents for obvious reasons such as taste, odour andappearance.

The problems associated with chemical constitutents arise primarilyfrom their ability to cause adverse effects after prolonged periods ofexposure; of particular concern are cumulative poisons and carcinogens.

There is either direct or indirect evidence that all of the substancesfor which guideline values have been recommended can cause harmfuleffects and are known to occur in water. It must remain a basic tenet ofpublic health protection that exposure to toxic substances should be aslow as possible. The guideline values indicate tolerable concentrations,but they must not be interpreted as defining targets for water quality.

Several of the inorganic elements for which guidelines have beenrecommended are recognised to be essential elements in human nutri-tion. No attempt has been made here to define a minimum desirableconcentration of such substances in drinking-water, except in the case offluoride, where the range of desirable concentration has been establishedfor many years. The guideline values are concentrations that should notbe exceeded over long periods of time because of the potential hazardsof ingesting excessive amounts of these substances. None of the organicsubstances for which values are recommended has any known beneficialproperties.

4.1.3 Basis of guideline valuesIn developing guideline values, the objective is to define a quality of

water that can be safely consumed by everyone throughout their lifetime.These guidelines represent an informed judgment based upon severalfactors, including:

(a) scientific criteria, defining dose-response relationships for substances;(b) analytical data on the frequency of occurrence and concentrations

of a substance commonly found in drinking-water; and(c) the potential application of suitable control techniques to remove

or reduce the concentration of a substance in drinking-water.The available data suggest that all chemical constituents for which

guideline values have been recommended can cause health problemsunder certain conditions. In general, these data have been obtained fromtoxicity studies in laboratory animals, or from human experiences in theoccupational setting. However, the health effects involved have usuallybeen observed at higher dose levels than those to which people areexposed by consuming trace quantities in drinking-water. Epidemiol-ogical studies are of only limited usefulness in determining cause-and-effect relationships for the chemical constituents found in drinking-water.For example, several such studies have examined the relationship betweenorganic chemicals in drinking-water and the increased risk of cancer, buthave provided no definite results that can be used to evaluate the risksassociated with individual organic substances found in drinking-water.

The guideline values are based on an assumed average consumptionof 2 litres of water per person per day for a person weighing 70 kg.

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4. CHEMICAL AND PHYSICAL ASPECTS

4.2 Health-related inorganic constituentsWHO Task Groups prepared a series of working papers dealing with

the health effects of 37 inorganic constituents in order to decide uponguideline values for the undesirable inorganic substances in drinkingwater.

4.2.1 Guideline values recommendedOn the basis of the health-related data concerning the 37 inorganic

constituents examined it was decided that, at the present time, guidelinevalues could be recommended for only 9 of them, as shown in Table 2.Boron has been added to the table, because of its occurrence in geoth-ermal waters in New Zealand and its significance as a substance whichadversely affects horticultural crops.

Discussion of the studies on which the guideline values are based, iscontained in Chapter 4 of Volume 1 of the WHO Guidelines for Drink-ing-Water Quality, which includes summaries of the evidence used insetting the guideline values.

Substances for which the World Health Organisation is unable torecommend a guideline value at present, have been omitted from theTables. When sufficient information is available guideline values maybe set and published in amendments to the Standards.

4.2.2 BoronThe WHO Guidelines for Drinking- Water Quality show in Table 7 of

Volume 1 that the Task Groups considered that the potential healthsignificance of boron in drinking-water did not justify further action atpresent. However the substance is present in some geothermal waters inNew Zealand and hence may contaminate some sources of drinking water.

Studies of the literature carried out in the Department of Health haveshown that boron is of relatively low toxicity, the male reproductivesystem being the most sensitive mammalian system) 920 The effects ofhigh levels of boron are reported to be irreversible, and in addition toeffects on the male reproductive system, include a reduction of growthand weight. Based on rat studies, a guideline value for humans is 5 g/m3.Boron is an essential trace element for plants but toxic when present inexcessive quantity. Acceptable levels in irrigation water vary 21,22 depend-ing on crop, climate and soil type. The guideline value of 0.5 g/m 3 ischosen to avoid plant toxicity in sensitive crops grown in glasshouses,i.e. plants obtaining all their water from irrigation.

4.2.3 FluorideAs fluoride is added to many water supplies to promote dental health,

the recommended range of concentration is given as the guideline valuesfor those drinking-water supplies where fluoride is naturally deficient.23

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4.3 Health-related organic contaminantsDuring the last decade the rapid expansion in knowledge about the

contamination of Water by organic substances in Europe, the U.S.A. andother industralised regions has made necessary the consideration of amuch broader range of such contaminants in present day drinking-water.

Although at least 600 organic substances have been identified in over-seas studies of water quality, the WHO Task Groups were able to limitdetailed study to about 20 groups of compounds. Further study producedthe list of substances for which guidelines are given in Table 3. Thesefall into the categories of chlorinated alkanes, polynuclear aromatichydrocarbons (PAH), pesticides, chlorobenzenes, chlorinated phenols,benzene and alkylaromatics and trihalornethanes.

4.3.1 Reservations relating to the guideline valuesAs there are considerable uncertainties in the evidence and inferences

on which the actual guideline values are set, they are deliberately cau-tious in character. It is also appreciated that it may be neither necessarynor feasible in every community to ensure that drinking-water qualitycomplies in every respect with the guidelines.

The guideline values given in Table 3 are measured as milligrams percubic metric (Mg/M3).. The evidence of toxicity from which the guidelinevalues are derived in many •cases is controversial, the dose-responsemodels dubious and the carcinogenicity, where alleged, is based on highdose animal data.

In the case of some of the organic compounds considered it is recog-nised that their most important influence on the quality of drinking-water is in relation to aesthetic and organoleptic aspects rather than healtheffects. Such substances could often render a water completely undrink-able at levels well below any that would give rise to concern from ahealth aspect.

4.3.2 Associated risks of lowering organic contaminationDrinking-water quality can affect the health and well-being of a com-

munity in a variety of ways. The importance of chemical contaminationinvolving trace amounts of substances (especially organic substances) mustbe assessed in relation to the other health risks associated with drinking-water (e.g., transmission of waterborne diseases of bacterial and viralorigin, and of parasites), and the relative importance attached to theserisks must be decided by taking into account the local or regional situ-ation. For instance, pesticides may be used to control disease vectors,and chlorine may be used for disinfection. In such situations, the risksassociated with low levels of organic compounds (e.g., pesticides, tn-halomethanes) may be smaller than the risk they are eliminating, andvalues higher than those given in Table 3 may be to the advantage ofthe consumer.

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4.3.3 Basis for guideline valuesThe basis for the guidelines is fully discussed in the WHO Guidelines

for Drinking- Water Quality, and the summaries of evidence used in set-ting guideline values are given.

4.3.4 Variations in listed substancesSome substances included in Table 3 of the WHO Guidelines have

been omitted from the New Zealand Standards and others included forthe reasons given below, and in 4.2. As information becomes availablein future, substances may be added to or deleted from Table 3.

4.3.4.1 Aldrin and DieldrinThese organochiorines are used in timber treatment in New Zealand

and may be present in sources of drinking-water. They have, conse-quently, been included.

4.3.4.2 Carbon tetrachlorideThis substance, which was formerly used as a cleansing agent and sol-

vent, is highly toxic. As it is not now in general use it has been omitted.

4.3.4.3 1, 1-DichloroetheneThis has been omitted because it is not likely to be present in New

Zealand waters.

4.3.4.4 Diquat and ParaquatThese substances are in use in some catchments to control water weeds.

The guideline levels have been derived from dietary no-adverse-effectlevels for rats. 24 If used as advised in "Herbicides for Aquatic WeedControl", Guides 1 to 3, Aglinks: FPP607, 9/81, FPP608, 9/81 andFPP6 19, 10/81 the substances should not be present in drinking-water.They are rapidly inactivated by contact with clay particles in soil, becomefirmly bound physically and hence, biologically inactive.

4.3.4.5 Heptachlor and heptachlor epoxideThese pesticides are not now used in New Zealand and are thus not

likely to be found in drinking-water. They have consequently been omit-ted from Table 3.

4.3.4.6 TrihalomethanesChlorination of drinking-water containing natural organic substances

produces a number of by-products including the trihalomethanes (THM):chloroform, bromodichloromethane, dibromochloromethane and tribro-momethane (bromoform). Chloroform has been shown to produce

39


cancer- in two species of laboratory animal. The other trihalomethanes,often formed when bromide ions are present, are only now being testedfor carcinogenicity in bioassays similar to those used to show that chlo-roform is a carcinogen under test conditions. These other trihalome-thanes are, however, known to be more active than chloroform in theAmes Salmonella test for mutagenicity.

It has been claimed that the results of laboratory tests of chloroformare supported by the conclusions of epidemiological studies in the U.S.A.But it has also been stated that the studies do not prove that increasedcancer rates are caused by trihalomethane compounds or other chemicalcompounds in water. They only suggest an association between the var-iables investigated. The reality of the increased risk of cancer cases allegedto be caused by chloroform in these studies lies somewhere between norisk and a maximum risk of 1.6 cases per million population per year.No experimental tools at present can define the true rate between thosetwo points with accuracy.25

Chlorine is, however, an effective water disinfectant and the hazardsof disease arising from microbiological contaminants resulting fromincomplete disinfection are substantial and must be recognised. Chlor-ine, which is the most widely used, convenient and easily controlleddisinfectant, is supported for use in water disinfection by the WorldHealth Organisation.

The formation of trihalomethanes is largely dependent upon the inter-action of chlorine and certain precursor substances in the water (e.g.fulvic and humic acids). A high THM concentration should not arise ifthe water contains small amounts of the precursors or if they are removedby treatment before chlorination. Considering the known health hazardsof biological contamination of drinking-water it is clear that inadequatedisinfection in order to control the THM level is not acceptable. WhereTHMs exceed guideline values, the Department of Health may recom-mend that studies of the means for reduction of levels of precursors inunchlorinated water should be undertaken.

Although a guideline value for chloroform only has been set in thesestandards, other countries, recognising a health risk in THMs; have setguideline values between 25 and 350 Mg/M3 for the sum of the fourspecific trihalomethanes mentioned above. These represent a judgmentof what is achievable in various circumstances set against what is desir-able, considering the uncertainty of the data.

In the absence of any firm data supporting a higher guideline value,the advice of the World Health Organisation has been accepted and aguideline value of 30 Mg/M3 for chloroform has been set.

4.4 Aesthetic and organoleptic aspects

The guideline values given in Tables 1 to 3 represent an informedjudgment based upon several factors, including (i) levels and frequencyof occurrence, (ii) toxicity and (iii) availability of control technology.

40


Substances affecting aesthetic and organoleptic quality are commonlyfound in drinking-water, seldom however at toxic levels, and controltechniques may be costly.

But the importance of the aesthetic/organoleptic quality of drinking-water should not be underestimated. An aesthetically displeasing sourcewater may lead the consumer to use a unsafe supply, and point-of-usetreatment devices are not necessarily a solution to this problem. More-over, taste, odour and colour may be the first signal of a potential healthhazard.

Since the majority of consumer complaints regarding water qualityrelate to its colour, taste, or odour, the quality of drinking-water, as per-ceived by the senses, largely determines the acceptibility of a particularwater. Stimulation of one sense organ influences to some degree the sen-sitivity of the organ of another sense. Sensation commonly attributed totaste is frequently in fact a combination of both taste and odour.

To guarantee that the majority of the consumers are unaware of thetaste or odour of a water constituent its concentration should be signifi-cantly lower than the threshold level. The latter is the concentration atwhich 50 percent of a group of individuals are able to detect the con-stituent in the water. A prerequisite of the test is that at least 10-15persons make up the group or panel and that they operate under con-trolled conditions; smaller panels reduce the accuracy and reliability ofthe determination.

Even so it is recognised that about 5 percent of the population ingeneral can still detect, via taste and smell, the presence of a substancealthough its concentration may be only 1 percent of the threshold value.26To suggest therefore that a drinking-water should be "free from taste andodour" could impose an unnecessary and unattainable standard on per-sonnel responsible for water quality.

Thus in an endeavour to provide a drinking-water free from taste forthe majority of consumers it has been found that the concentration oforganic substances in particular must be restricted to levels below 10percent of their particular taste and odour threshold values.

Although many individual organic substances in water have been asso-ciated with an adverse taste, this document deals only with chemicalsthat occur frequently as contaminants in drinking-water and for whichanalytical methods are generally available.

A "two-level" system of guideline values has been used in Table 4because of the nature of the parameters. "Highest desirable" applies toa water which would be generally acceptable to consumers. Values greaterthan those listed under "Excessive level", would markedly impair thepotability of the water.

Local circumstances may occur where perceptible odour and taste ofa drinking-water is unavoidable, and removal methods either of dubiousefficiency or not available. In such instances the Department of Healthshould be approached for advice, if a technical solution is not available.

As with taste and odour, the appearance of water can also cause con-sumer complaints. Discolouration, with or without particulate matter,

41


this. When the chlorine used for disinfection reacts with organic com-pounds, unacceptable levels of chlorinated organic contaminants may beproduced. Effective coagulation, changes in chlorine dosage and pointsof application, and the use of alternative disinfectants can all reduce thelevels of chlorinated organic compounds. Many organic contaminantscan be removed from treated water by passing it through activated-car-bon filter beds, but the effectiveness of the filters varies with the type oforganic contaminant. Fouling and the growth of organisms on the carbonbed can also adversely affect the efficiency of this treatment. Nitrate levelscan be reduced at the treatment works by a biological denitrificationprocess or, at much greater cost, by ion exchange. The most appropriatecourse of action for any given problem can only be judged by the controlagency familiar with the local conditions and the technology available.

4.6.2.3 Distribution systemContaminants can enter a potable water distribution system through

cross-connections, back-flows, breakages or leaks or they may be intro-duced from materials used in the construction of the system. Such prob-lems can usually be overcome by proper management and a preventivemaintenance programme.

4.6.2.4 Water treatment chemicals and construction materialsToxic chemicals in drinking-water that are derived from treatment

chemicals or construction materials used in water supply systems arebest controlled by appropriate specifications for the chemicals andmaterials used. 27 For example, a wide range of polyelectrolyte coagulantaids is now available and the presence of residues of unreacted monomermay cause concern.28

4.6.2.5 Effectiveness of remedial measuresRemedial action to solve one contamination problem should not lead

to creation of new problems. Any changes introduced in water treatmentand distribution must be carefully monitored to ensure that the remedialaction has been effective. This can be particularly difficult if the contam-ination is intermittent but with a good follow-up system, efficient feed-back of results and careful record-keeping, a reliable assessment can usu-ally be made. In fact, with a systematic build-up and review of opera-tional and water quality data, it may even be possible to forecast andforewarn of some of the problems of water quality that are likely to ariseand to adopt appropriate preventive measures.

4.6.3 Corrective measures related to the aestheticquality of drinking-water

Every effort should be made to produce drinking-water whose colour,turbidity, odour, and taste are acceptable to consumers. Failure to do so

44


will result in complaints and, in some cases, in the use of alternativeunsatisfactory sources of drinking-water. High levels of turbidity can alsolead to disinfection difficulties.

A high proportion of the capital investment in water treatment plantmay be directed at processes for the control of colour and turbidity. Thetechniques usually employed include chemical coagulation followed bysedimentation and filtration. 29 There is no basic difficulty in achievingthe values recommended in the standards, but a significant cost isinvolved.

At times, judicious relocation of the water intake may resolve tasteand odour problems. Processes for the control of tastes and odours inthe water supply are well established. When there are intermittent tasteand odour problems, powdered activated carbon may be used. In somecases the taste and odour of water can be improved by aeration or break-point chlorination. Where taste and odour are a continuing problem,because of the contamination of the source water, it may be necessaryto use more expensive forms of treatment, including oxidation with ozoneor adsorption on granular activated-carbon filters.

Tastes and odours often arise within the distribution system as a resultof biological growths or occasionally of contamination by materials usedduring construction or repair of the system. Regular monitoring of thetaste and odour of the water passing into the supply helps to identifythis kind of problem, whose solution requires a different approach. Checkson water samples taken from various parts of the distribution systemusually enable the source of the contamination to be identified. Tasteand odour problems can be minimised by preventive maintenance ofthe distribution system, including regular swabbing and flushing, and inextreme cases by mechanical scraping of the pipelines.

Iron and manganese can be removed from water by aeration or byother oxidative treatment (chlorine, chlorine dioxide, potassium per-manganate) at an elevated pH followed by sedimentation and filtration,as. necessary. In some cases a special filter medium can be used whichminimises the requirement for oxidation.

Iron and aluminium are sometimes present in tap-water as a result oftheir use as coagulants in water treatment. This can lead to serious com-plaints and usually indicates unsatisfactory pH control, unsuitable con-ditions for coagulation, filter breakthrough or some other failure in thetreatment process.

Copper, zinc, and iron may occur in drinking-water as a result of cor-rosion of pipework. This can be corrected by anti-corrosion treatmentor by replacement with pipes made from an alternative material.

The guideline values recommended for total dissolved solids, hard-ness, sodium, chloride, and sulfate will be of value mainly in providinga basis for source selection, since the desalting processes necessary forpurification are non-selective and very expensive. However, where noother sources are available, processes such as reverse osmosis, electro-dialysis, or distillation may have to be considered.

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5. RADIOACTIVE MATERIALS INDRINKING-WATER

5.1 IntroductionEffects of radiation exposure are called "somatic" if they become man-

ifest in the exposed individual, and "hereditary" if they affect his des-cendants. Malignant disease is the most important delayed somaticeffect. 3°

For some somatic effects such as carcinogenesis, the probability of aneffect occurring, rather than its severity, is regarded as a function of dosewithout a threshold ("stochastic effect") whereas for other somatic effectsthe severity of the effect varies with the dose ("non-stochastic effects"),a threshold may therefore occur for such effects.30

The aim of radiation protection is to prevent harmful non-stochasticeffects and to reduce the probability of stochastic effects to a level deemedacceptable. To achieve this objective, dose-equivalent limits are setsufficiently low that the threshold dose is unlikely to be reached duringa complete life-span.

Various body tissues have different sensitivities to radiation exposure•and the International Commission on Radiological Protection (ICRP),in an endeavour to provide measures of equal risk, introduced the con-cept of dose-equivalent weighting factors. A measure of the total riskfrom non-uniform radiation exposure is the effective dose-equivalent,HE.

Long-lived radionuclides are retained for very long periods in the bodyand consequently the resulting personal exposure may extend over manyyears. The committed effective dose-equivalent (H E5O) resulting from anintake of radioactive material into the body is the effective dose-equiv-alent that will be accumulated during the 50 years following the intake.3'

The guideline values adopted have been decided by WHO in associa-tion with the International Commission on Radiological Protection(ICRP).

5.2 Nature of the guideline valuesThe guideline values proposed are based on an assumed daily intake

of drinking-water of 2 litres and the dose resulting from a given intakeof radioactive material has been calculated on the basis of the metabo-lism of an adult. Deviations from these assumptions, e.g. the influenceof age on metabolism, or larger intakes of drinking-water, are not con-sidered likely to necessitate modification of the screening or guidelinevalues recommended since the latter provide a large margin of safety.

46

5. RADIOACTIVE MATERIALS IN DRINKING-WATER

The guideline values given apply only to routine operational condi-tions. The National Radiation Laboratory of the Department of Healthwould assist water supply authorities to deal with any emergency situ-ations which might arise.

5.3 Guideline values recommendedThe guideline values recommended take account of both naturally-

occurring radioactivity and any radioactivity that may have reached thewater sources as a result of man's activities. From a radiological pointof view, they represent a value below which water can be consideredpotable without any further radiological examination.

The guideline values set are:gross alpha activity: 0.1 BaIlgross beta ctivity: 1 Bq/l

Becquerel (Bq) is a unit of activity of an amount of radionuclide; 1becquerel is equivalent to I spontaneous nuclear transformation persecond and corresponds to approximately 27 picocuries, the guidelinevalues are applicable to the mean of all radioactivity measurementsobtained during a sampling period appropriate to the source water. Thefrequency of sampling is a matter of judgment, but it should be sufficientto establish confidence in the water quality. As the techniques of sam-pling and testing waters are beyond the capabilities of water supplyauthorities, the National Radiation Laboratory provides a surveillanceand monitoring system, and publishes the results.32

As there are virtually no man-made discharges of radioactive sub-stances in New Zealand the source of any radioactivity is likely to beattributable to fall-out from nuclear testing. The monitoring of radio-activity in rainwater is regularly conducted by the NRL and the resultspublished.32

5.4 Interpretation of guidelinesThe guideline values have been established in order to demonstrate thatin conjunction with the surveillance and monitoring systems, the con-centrations of radioactive materials present in drinking-water do not rep-resent any significant hazard.

The measurements of gross alpha and gross beta activity which haveto be compared with the guideline values, only serve to place some upperlimit on the associated hazard. If the guideline values are exceeded, moredetailed analyses of the water will be necessary to allow the hazard tobe assessed. Only then will it be possible for the Department of Healthto decide whether or not any hazard, justifying corrective action, ispresent.

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REFERENCES

1. WHO (1978) Environmental Health Criteria No. 6, Principles and Methods for Eval-uating the Toxicity of Chemicals. Part 1. Geneva, World Health Organisation, 272 pp.

2. Department of Health, New Zealand. 1980 Grading of Public Water Supplies in NewZealand Board of Health Report Series: No. 27. Wellington, 1980.

3. WHO (1976) Surveillance of drinking-water quality. Monograph Series No. 63, Geneva.4. International Reference Centre for Community Water Supply and Sanitation, Guide-

lines on health aspects of plumbing (in press).5. Cox. C. R., Operation and control of water treatment processes, Geneva, WHO 1969.

Monograph Series No. 49.6. WAGNER. E. G. & LANOIX, J. N. Water supply for rural areas and small communities,

Geneva. WHO 1959. Monograph Series No. 42.7. WAGNER, E. G. & LAN0Ix, J. N. Excreta disposal for rural areas and small commu-

nities, Geneva, WHO 1958. Monograph Series No. 39.8. FEACHEM, R. G. et al. Appropriate technology for water supply and sanitation. Health

aspects of excreta and sullage management: a state-of-the-art review. Washington, D.C.The World Bank, 1980.

.9. Local Government Training Board. Instruction and Training Manual for WaterworksOverseers, Foremen and Servicemen. Series No. 8, Wellington (1982).

10. Microbiological Society's Committee on Coliform Bacteria. Definition of terms con-cerning coliform bacteria and recommended methods for their detection. New ZealandJournal of Science, 1976, Vol. 19, 215-19.

Ii. ASSAR, M. Guide to Sanitation in Natural Disasters (1971) World Health Organisation,Geneva. - - -

12. Department of Health, New Zealand. Drinking-water for Campers, Trampers andHouseholders in Emergencies, Health Information Series Pamphlet No. 178, Wellington.

13. Department of Health and Social Security. The Bacteriological Examination of WaterSupplies. Reports on Public Health & Medical Subjects No. 71. London, 1969.

14. American Public Health Association. Standard Methods for the Examination of Waterand Wastewater. 15th Edition. Washington, DC. APHA, AWWA, WPCF (1980).

IS. REASONER, D. J. et al. Rapid seven hour faecal coliform test. Applied & EnvironmentalMicrobiology 38. 229-236 (1979).

16. WHO (1971) International Standards for Drinking- Water. Third edition.17. WHO Human Viruses in Water, Wastewater and Soil. Geneva, WHO, 1979. Technical

Report Series 639. - -18. American Public Health Association, Control of Communicable Diseases in Man, 13th

edition, APHA, Washington (1980). -19. DIXON et al. Environmental Health Perspectives, Vol.. 13. 1976.20. KR0sAvSKII el al. Environmental Health Perspectives, Vol. 13. 1976.21. WILLIAMS. J. G. Water Quality Criteria for crop irrigation ADAS Quat. Rev. 7: 106-122

(1972).22. WILLCOX, L. V. Determining the quality of Thigation water Agricultural Information

Bulletin No. 197, U.S. Dept of Agriculture (1958).--23. Department of Health, New Zealand, Technical Memorandum on Fluoridation Prac-

tice (1973). - -24. British Crop Protection Council, The Pesticide Manual London (1979).25. KHORDAGUI AND MANCY Formation of Trihalomethanes during disinfection of drink-

ing-water Water Quality Bulletin, Vol. 18 No. 1, Canada 1983.26. ZOETEMAN, B. C. J. (-1980) Sensory assessment of water quality. Pergamon Press, Oxford.27. WHO. Treatment agents and processes for drinking-water and their effects on health.

• Report of a working group. Copenhagen, WHO, 1978.28. WHO International Reference Centre for Community Water Supply. Health aspects

of the use of polyelectrolytes in water treatment for community water supply. Tech.Paper Series No. 5. The Hague, The Netherlands (1973).

29. International Reference Centre for Community Water Supply and Sanitation. SmallCommunity Water Supplies. Technical Paper Series No. 18, The Hague (1981).

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30. International Commission on Radiological Protection. Recommendations of the Inter-national Commission on Radiological Protection Annals of the ICRP, 1977, ICRPPublication 26.

31. International Atomic Energy Agency. Basic safety standards for radiation protection.Vienna, IAEA, 1982 (Safety Series No. 9).

32. National Radiation Laboratory, Review for the Years 1976-1980, Department of Health,New Zealand, Report NRLAR 26, Christchurch (1980).

33. Official Journal of the European Communities, Council Directive of 15 July 1980 relat-ing to the qualm' of water intended . for human consumption (80/778/EEC).

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Documents

Ministry of Health NZ - TACK...1. INTRODUCTION 1.1 Consumer perception of drinking-water quality The consumer of drinking-water relies completely upon his senses to assess its quality