UK; Greywater Recycling: An Information Guide

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Greywater: an information guide


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Environment Agency Greywater: an information guide 1

We are the Environment Agency. It's our job to look after

your environment and make it a better place - for you, and

for future generations.

Your environment is the air you breathe, the water you drink

and the ground you walk on. Working with business,

Government and society as a whole, we are making yourenvironment cleaner and healthier.

The Environment Agency. Out there, making your

environment a better lace.

Published by:

Environment AgencyRio HouseWaterside Drive, Aztec West

Almondsbury, Bristol BS32 4UDTel: 0870 8506506Email: [email protected]

Environment Agency April 2008

All rights reserved. This document may be reproduced withprior permission of the Environment Agency.


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Environment Agency Greywater: an information guide2

ContentsIntroduction.........................................................................................................3Types of systems available...............................................................................5Supply and demand ...........................................................................................9Regulations.......................................................................................................11Cost-effectiveness ...........................................................................................16Energy ...............................................................................................................19Conclusions......................................................................................................21References ........................................................................................................22Glossary of terms.............................................................................................24List of abbreviations ........................................................................................25


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1. IntroductionGreywater is wastewater from showers, baths, washbasins, washing machines and kitchen sinks. It

can be collected from some or all of these sources and, after treatment, used for purposes aroundthe home such as toilet flushing or garden watering that do not require drinking water quality.

This guide defines greywater as wastewater only from showers, baths and hand basins. It excludesthe more contaminated water from washing machines and kitchen sinks. Greywater reuse is theuse of untreated greywater and greywater recycling is the use of treated greywater.

Recent years have seen increased interest in green technologies and greywater recycling is noexception. This publication focuses on systems for domestic uses and is intended for homeowners,house builders, planners, architects and building managers. It discusses:

different types of systems available; design, installation and maintenance requirements; economic and environmental issues.

1.1 Why recycle greywater?

Although England and Wales appear to enjoy plenty of rainfall, their increasing population and thechanging climate mean that water resources are under pressure especially in south-eastEngland. There is less water available per person in south-east England than in manyMediterranean countries. The large number of new houses being constructed in this region overthe next few years will increase the competition for available water between the environment andpeople.

If used for toilet flushing, a well-designed and fully functional greywater system could potentiallysave a third of the water used in the home. Recycled greywater could also cater for other uses forwhich potable water quality is not essential such as garden watering or vehicle washing. Thegreater the proportion of recycled water used, the less mains water will be needed thereby easingthe pressure on water resources. Chapter 3 describes this in more detail.

Recycling greywater not only reduces the consumption of mains water, it also reduces the volumeof water discharged into the sewerage system. Consumers with water meters could therefore savemoney on both their water supply and wastewater bills. The economics of recycling systems arecovered in more detail in chapter 5.

At present greywater systems are not common in England and Wales. This may be because:

systems are expensive to purchase, maintain and run, while the cost of water is relativelylow;

only a third of domestic customers have metered water supplies and thus would savemoney;

there are no regulations covering the quality of recycled water; the reliability of greywater systems has been poor in the past and remains unproven.

Other countries have embraced the technology:

Many greywater systems are installed each year in Germany. Australia offers grants for the installation of greywater systems. In Tokyo, greywater recycling is mandatory for buildings with an area >30,000 m

2or with a

potential non-potable demand of more than 100 m3/day (CBSE 2003).

Cyprus subsidises the use of greywater for toilet flushing and garden irrigation by offeringsubsidies of 1700. The subsidy is valid up to 1 December 2008

1.

1http://www.cyprus.gov.cy/moa/WDD/WDD.nsf/applications_en/applications_en?OpenDocument


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In the UK, the Code for Sustainable Homes2

launched in December 2006 sets a range of standardsfor water use per person in newly built houses. To meet the highest levels of the code, the internalper person daily water use has to be less than 80 litres. To meet this target, either greywater orrainwater harvesting is likely to be needed.

2http://www.planningportal.gov.uk/england/professionals/en/1115314116927.html


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2. Types of systems availableGreywater recycling systems vary significantly in their complexity and size from small systems with

very simple treatment to large systems with complex treatment processes. However, most havecommon features such as:

some sort of treatment facility; a tank for storing the treated water; a pump; a distribution system for transporting the treated water to where it is needed.

All systems that store greywater have to incorporate some level of treatment, as untreatedgreywater deteriorates rapidly in storage.

This rapid deterioration occurs because greywater is often warm and rich in organic matter such asskin particles, hair and soaps/detergents. This warm, nutrient-rich water provides ideal conditions

for bacteria to multiply, resulting in odour problems and poor water quality. Greywater may alsocontain harmful bacteria, which could present a health risk without adequate water treatment orwith inappropriate use. The risk of inappropriate use is higher where children have access to thewater.

Greywater systems can be grouped according to the type of treatment they use. Note that thecommercially available systems quoted in this guide are for illustration only.

3The Environment

Agency does not recommend any particular manufacturer or system.

2.1 Direct reuse systems (no treatment)

It is possible to reuse greywater without any treatment provided that the water is not stored for longbefore use. For example, once bath water has cooled, it can be used directly to water the garden.Very simple devices are available to make this practical. Among these is the WaterGreen byDroughtbuster UK Ltd,

4which is essentially a hose pipe with a small hand pump to create a siphon.

This allows cooled bath water to be taken directly from the bath and sent through the hose to thegarden (usually via an open window).

Using greywater in this way may not be for everyone, but it does provide an inexpensive and easyway of saving water while avoiding the issues that arise when greywater is stored for any length oftime. It is particularly useful for keen gardeners when water use restrictions are in place. Expertsusually advise that greywater should not be used on fruit or vegetable crops. See our website(http://www.environment-agency.gov.uk/savewater) for more information on water efficientgardening.

Equipment is also available to allow more integrated direct reuse of greywater. For example, avalve can be fitted to an external waste pipe that drains water from the bath or shower. This valvecan be used to direct greywater to a water butt where, once cooled, it can be used for gardenirrigation. An example of this type of valve is the Water Two

5valve, which can be fitted to existing

piping and switched to either divert greywater to drain or to storage. As there is no treatment, it isimportant that the greywater is not stored for long as the water quality deteriorates rapidly.

2.2 Short retention systems

These systems take wastewater from the bath or shower and apply a very basic treatmenttechnique such as skimming debris off the surface and allowing particles to settle to the bottom of

3All company websites cited in this guide were available as of 14 April 2008.

4http://www.droughtbuster.co.uk

5http://www.watertwo.co.uk/index.htm


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the tank. An example of such a system is the Ecoplay unit,6

which aims to avoid odour and waterquality issues by treating the greywater to a basic standard and ensuring the water is not stored fortoo long. If it is not used within a certain time, the stored treated water is released and the systemis topped up with mains water. However, potential water savings are dependent on usage patterns.

Using the simplest level of treatment makes these systems relatively cheap to buy and run, whilereducing the risk of equipment failure leading to expensive repairs. According to the Ecoplaywebsite,

6Ecoplay is maintenance freewith no filters to clean or replace. Another benefit of these

systems is that they can be located in the same room as the source of greywater, thus reducing theneed for expensive, dual-network plumbing.

Ecoplay is limited to the domestic market (including hotels) where it can be installed in a bathroomand the balance of shower use and toilet flushing allows it to operate effectively. The product issuited to installation in newly built homes and renovation projects, but is not recommended forretrofitting. The systems reliability, maintenance requirements and long-term savings are, as yet,unproven.

2.3 Basic physical and chemical systemsSome systems use a filter to remove debris from greywater prior to storage while chemicaldisinfectants (e.g. chlorine or bromine) are used to stop bacterial growth during storage. The use ofdisinfectant has an environmental impact as well as cost implications. Both need to be consideredin overall costs and benefits.

A study by the Environment Agency (NWDMC 2000) of this type of system reported:

a range of water savings from less than 6 to over 32 per cent of total water use; variable reliability; filters required regular cleaning to avoid blockages; odour problems due to either poor water quality or high levels of disinfectant; instances where the system had failed and switched to mains back-up with users unaware

of the failure.

Several other studies have looked at the water saving potential of these systems and have alsoencountered similar reliability issues. For example, South Staffordshire Water installed andmonitored physical/chemical greywater systems in a block of flats and found them unreliable.

7

Some residents were initially happy with the systems but, with time, residents identified problemssuch as odour, performance, noise and water quality. These problems were exacerbated bydifficulties in gaining access to the systems in the flats for service and repair, and eventually led totheir removal. The payback was estimated at over 65 years which, in this case, was significantlylonger than the life of the systems. This project highlighted the technical and practical issues thatcan occur with the installation of basic greywater systems. For example, access issues could have

been avoided if a communal system had been installed instead of individual systems in each flat.

A study by Thames Water in conjunction with Cranfield University monitored the effectiveness offive individual household scale greywater systems between April 1999 and May 2000 (Hills et al.2002). The systems studied were very similar to those described in the earlier Environment Agencyreport (NWDMC 2000). The systems used basic filtration and chemical disinfection (bromine) totreat the greywater. Of the five houses investigated, one produced no data due to monitoringdifficulties and another was often left unoccupied. This left three systems producing representativedata, with savings of 921 per cent of total consumption. Systems were unreliable and users oftendid not know when the systems had failed. Problems were identified during regular, routine systemchecks by project staff and faults fixed quickly. But even with this support in place, the poorreliability of the systems meant the actual savings realised were significantly below the expected40 per cent of total domestic consumption. All the systems were serviced in January 2000 (nine

6http://www.ecoplay-system.com/default.aspx?id=1

7South Staffordshire Water, 2004 A Study on the Effectiveness of Grey Water Recycling Technology.

[Unpublished].


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months into the trial) and appeared to operate properly until May. But when they were revisited inJanuary 2002, only one out of the five systems was functioning properly and this had beenserviced one month previously.

2.4 Biological systemsBiological systems vary in their complexity and form, but the concept is the same: bacteria areused to remove organic material (contamination) from wastewater. The process uses the sameprinciples employed at sewage treatment works. Oxygen is introduced to wastewater to allow thebacteria to digest the organic contamination. Different systems supply oxygen in different ways;some use pumps to draw air through the water in storage tanks while others use plants to aeratethe water.

In nature, reeds thrive in waterlogged conditions by transferring oxygen to their roots. Biologicalsystems generally use reed beds to add oxygen to wastewater and allow naturally occurringbacteria to remove organic matter. Wastewater can be passed through the soil/gravel in which thereeds are growing and the bacteria fed by oxygen from the reeds and nutrients from the

wastewater decompose the waste. Reed beds are an established method for treatingwastewater/sewage and can also be used to treat greywater. However, they require a certainamount of expertise and a suitable, relatively large outside area.

Water Works UK markets a system called GROW (Green Roof Water Recycling System8). This

system uses a series of gravel-filled troughs which filter greywater through a reed bed containingactive bacteria. The greywater is pumped to the gravel troughs where it passes through the filtermedia for around 18 hours. This filtered water then passes through an ultraviolet (UV) filter to killany remaining bacteria and is dyed green to distinguish it from potable water. A second system(GROW2) is now available, which can be positioned in the garden if no appropriate roof area isavailable.

9

2.5 Bio-mechanical systemsThe most advanced domestic greywater treatment systems use a combination of biological andphysical treatment. An example of such a system is the AquaCycle 900.

10This system was

developed in Germany, where mains water is more expensive than in the UK (Ofwat 2005) andwhere greywater systems are more common. The AquaCycle 900 is a substantial system aboutthe size of a large fridge, which means it needs to be installed in a basement or garage. It is bestinstalled during construction and is not suited for retrofitting into existing buildings due to cost andother practical difficulties.

The AquaCycle 900 is an all-in-one unit which treats and stores water in three enclosed tanks.Greywater is filtered through self-cleaning filters as it flows into the storage unit. Organic matter isremoved by microbial cultures formed on rubber chips. Solid material is allowed to settle to thebottom of the tank and is removed automatically. The system encourages bacterial activity bybubbling oxygen through the water. The final stage of the system is UV disinfection to remove anyremaining bacteria. This process claims to produce treated water that meets EU bathing waterstandards.

Another commercially available all-in-one system is the WME-4,11

which uses biological pre-treatment through aeration and then membrane filtration to produce high quality treated greywater.

Combining physical and biological treatment generally produces the highest quality water, but italso uses a significant amount of energy (see chapter 6), is expensive to purchase and operate(the AquaCycle 900 costs around 3,000 to buy), and maintenance costs are uncertain.

8http://www.wwuk.co.uk/grow.htm

9http://wwuk.co.uk/grow2.htm

10http://www.freewateruk.co.uk/domestic-greywater-IV.htm

11Http://www.aqua-lity.co.uk/en/products/control_units/aqua_recycling_control_wme_4/index.html


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This high level of water quality may not be required if the use of treated greywater is restricted in anindividual property to toilet flushing. But where stored greywater is treated to a high standard, thereis potential for its use in other applications such as vehicle washing. A high standard of waterquality may also be required in communal systems to overcome both real and perceived risksassociated with the treated water.


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Toilet

Shower, bath

and basin

Kitchen sink

Washingmachine

Dishwasher

Outdoor

3. Supply and demandAverage water use in England and Wales is just under 150 litres per person per day (Ofwat 2007).

About a third of this is used for toilet flushing and this proportion could potentially be replaced bytreated greywater. Figures 1 and 2 show how water is used in existing and new build homesrespectively.

Figure 1: Typical water use in an existing home

Source: Environment Agency (2007)

Figure 1 shows that the volume of water used to flush the toilet in a typical household is slightlysmaller than the volume of water available from showers, baths and washbasins. Thus it seemsthat water demand for toilet flushing could be met by recycling greywater. This would providesignificant savings as toilet flushing represents a relatively large proportion of household demand.

Figure 2 shows that the way we use water is changing. The key issue is the decreasing proportionof water used for toilet flushing and the increasing proportion used for washing. This is due to theinstallation of progressively lower flush toilets and the trend for high water consumption showers

and mains pressure hot water systems. Although there is still more than enough greywateravailable to meet the demand for toilet flushing, the savings would be lower. Where ultra low flushtoilets are installed, these potential savings become smaller still. Smaller water savings lead tolonger payback periods so, as toilet technologies improve, the potential for water saving throughgreywater recycling reduces.

Water use patterns vary widely between households. This has consequences for the suitability ofgreywater systems in specific households. For example, some households may use a large amountof water for showering and bathing in the morning and evening, and spend most of the day at workwhere other toilet facilities are available. This situation would produce a surplus of greywater andwater savings would be minimal. An alternative situation could arise where occupants have a lowuse of water for bathing and spend the majority of the day at home, therefore using a larger amountof water for flushing the toilet. This would create a higher demand for treated greywater than the

quantity available and would also lead to minimal water savings.


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Toilet

Shower, bath

and basin

Kitchen sink

Washing

machine

Dishwasher

Outdoor

Figure 2: Typical water use in a new home

Source: Environment Agency (2007)

Most greywater systems require some kind of regular maintenance. While some householders maybe keen to get involved, others may be unwilling or unable to do so. If maintenance is not carriedout, systems may fail and savings will be reduced. The cost of professional maintenance will furtherextend payback periods.

Communal greywater systems can potentially avoid the problem of uneven supply and demandencountered by a single household system as peoples different consumption patterns cancel eachother out. Maintenance may also be easier cheaper per household and of a higher standard as itcan be undertaken by dedicated staff.

However, studies into perceptions of communal recycling schemes have found that people wouldprefer to reuse their own greywater rather than someone elses (Jeffrey 2002). Studies have alsoshown that, where communal systems are installed, people prefer larger city wide schemes wherethe source of the water is anonymous to more local schemes where they may know many of thepeople involved (Po et al. 2003).

User acceptability is also a function of the type of usage. For example, the use of recycled water for

golf courses, parks and industry is relatively easily accepted by the community, but the use ofrecycled water becomes less popular inside peoples homes. Within this, acceptability is lower forwater uses where contact with the recycled water is greater (e.g. bathing) than it is for water useswhere contact is minimal (e.g. toilet flushing) (Jeffrey 2002).

Using greywater as a source of non-potable water can provide a more reliable and consistentsupply of water than that available from rainwater harvesting. This is a distinct advantage over theuse of rainwater as a supply of non-potable water. The supply of greywater will be reliablethroughout the year, reducing the amount of mains back-up required at peak times when the mainswater supply is already stretched.


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4. Regulations

4.1 Water qualityWater quality is a wide term covering physical, chemical and biological quality.

Physical quality includes how clear the water is (i.e. turbidity), total suspended solids inthe water and its temperature.

Chemical quality includes how acid or alkaline the water is (i.e. pH), how muchdisinfectant is present (residual chlorine or bromine), the amount of dissolved oxygen in thewater and biochemical oxygen demand (BOD) a measure of the amount of organicmaterial in the water.

Biological quality mainly relates to the presence of bacteria and viruses. The groups ofbacteria chosen as indicators of biological water quality are those abundant in human andanimal faeces. Their presence indicates the presence of faecal contamination.

It is important that the water we use is fit for purpose. Recycled greywater will not be of the samewater quality as mains water, but what does this mean? What risks does this present? And howclean does the water need to be?

Greywater from showers, baths and washbasins will often be contaminated with human intestinalbacteria and viruses as well as organic debris such as skin particles and hair. Greywater will alsocontain residues of soaps, detergents and other cosmetic products; these often contain nutrientsthat help bacteria develop. This combination of bacteria, organic material and nutrients providesideal conditions for bacteria. This is exacerbated by the relatively high temperature of greywater,which can encourage the growth of bacteria further. This is why untreated greywater should neverbe stored for more than a few hours.

The most significant risk from greywater is exposure to pathogenic micro-organisms derived fromfaecal contamination. However, the physical and chemical characteristics of greywater are alsoimportant as these can encourage the growth of bacteria, interfere with treatment or disrupt theoperation of fittings that use water. For these reasons, the physical, chemical and biological waterquality of greywater must be suitable for its intended use.

While stringent standards guard potable water quality in the UK, there are no regulatory standardsconcerning the quality of non-potable water. Many groups have called for appropriate standards fornon-potable water to overcome concerns about potential health hazards and to bolster publicconfidence in using non-potable water, but the enforcement of such standards would be difficult asmost systems are independently owned and maintained.

The Water Supply (Water Quality) Regulations 200012

(as amended) are enforced by the DrinkingWater Inspectorate13 and specify the quality standards for drinking water. Experts believe these aretoo strict to apply to water not intended for drinking. One alternative basis for water qualitystandards is the Bathing Water Directive,

14which works on the principle that water that meets the

bathing water quality criteria should be safe for total immersion and occasional ingestion. Waterthat meets its standards should therefore also be safe for flushing toilets and watering the garden.

The Governments Market Transformation Programme (MTP) recently examined the potential fordeveloping water quality standards for non-potable water (rainwater and greywater) (MTP 2007).This work was carried out by the Buildings Services Research and Information Association (BSRIA)and built on principles discussed in the Buildings that Save Water(BTSW) project (CIRIA 2001).The MTP report recommends that the guidelines should be based on the Bathing Water Directives(1975 and 2006) and identifies different guidelines for different end uses (see Table 1).

12Statutory Instrument 2000 No. 3184 (http://www.opsi.gov.uk/SI/si2000/20003184.htm)

13http://www.dwi.gov.uk

14http://ec.europa.eu/water/water-bathing/index_en.html


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The three microbiological water quality indicators suggested are those used in the Bathing WaterDirectives. These are:

Total coliforms Escherichia coli Enterococci.

The report also identifies a traffic light system for interpreting the guidelines (see Table 1).

The MTP guidelines identify three categories of water quality required depending on the riskassociated with the intended use.

Category A External cleansing requires the highest level of water quality as this usagecreates aerosols that can be inhaled, increasing the risk of pathogens entering the body.

Category B Drip irrigation allows considerably more bacteria per 100 ml than Category Abecause human exposure is lower. It also does not require the water to be as clear asrequired for Category A.

Category C WC flushing allows the same level of bacterial contamination as Category B,but allows a higher residual chlorine or bromine concentration. It also specifies how clearthe water should be because the water has to be visually and practically acceptable fortoilet flushing.


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Table 1: MTP proposed guidelines for the water quality of non-potable water from rainwaterand greywater

Source: MTP (2007)


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4.2 Water fittings

As recycled greywater will not be of drinking water quality, it is important to manage the risk ofcross-contamination with the drinking water supply appropriately. This risk is higher in systems

designed to serve more than one property because the recycled water network is more complex.

At a site in Holland in 2001, for example, an accidental cross-connection was made between thepotable water supply and a communal non-potable supply intended for garden watering, toiletflushing and laundry use. It was a week before this error was identified and it caused an outbreakof gastroenteritis in about 200 people (CRC 2003). This example is a reminder of the importance ofprotecting the mains water supply from contamination and ensuring cross connections are notmade between potable and non-potable water.

The Water Supply (Water Fittings) Regulations 199915

govern the protection of the mains watersupply in England and Wales. They apply to all plumbing systems, water fittings and equipmentsupplied from the public water supply.

Greywater systems nearly always feature a mains back-up so they can be topped up with mainswater should demand for treated greywater be greater than supply. Where this is the case, asuitable type AA, AB or AD air gap

16must be used to ensure there is a physical separation

between the greywater and the mains water to prevent contamination of the mains supply.

To manage the risk of accidental cross-connections between potable and non-potable supplies, it isimportant to follow the good practice described in Guidance on Marking and Identification ofPipework for Reclaimed (Greywater) Systemsproduced by the Water Regulations AdvisoryScheme (WRAS) (WRAS 1999). Figure 3 shows the suggested labelling of internal pipes,containing reclaimed water.

Figure 3: Suggested labelling of internal pipes containing reclaimed water

Source: WRAS (1999)

The WRAS guidelines also recommend reclaimed water pipeline apparatus is identified on markerplates through colour coding and wording (i.e. RECLAIMED WATER in black letters on a greenbackground). An example is shown in Figure 4.

15Statutory Instrument 1999 No. 1148 (http://www.hmso.gov.uk/si/si1999/19991148.htm) and Statutory

Instrument 1999 No. 1506 (http://www.opsi.gov.uk/si/si1999/19991506.htm)16

As defined in Defra guidance seehttp://www.defra.gov.uk/environment/water/industry/wsregs99/guide/section6.htm


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Figure 4: Typical reclaimed water marker plate as shown in the WRAS guidelines

Source: WRAS (1999)


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5. Cost-effectivenessThe cost-effectiveness of greywater systems is as variable as the systems themselves. The

amount of money saved will depend on:

volume of water saved; price of the mains water replaced; costs of installing, running and maintaining the greywater system.

If you use a large volume of water to irrigate your garden and you purchase a simple system todivert cooled bath water, you could make substantial savings with very little capital investment.

In contrast, if you install an expensive bio-mechanical greywater system just for toilet flushing inyour house, you are unlikely to see any return on your investment.

Before investing in a greywater system, it is worth calculating what sort of savings you are likely to

see on your water bill.

A simple cost savings calculation can be carried out using standard usage figures for toilets (seeTable 2). You can adapt the calculation to reflect your individual situation by adjusting occupancy,toilet flush volume and the cost of water and sewerage in your area (or adding outdoor use). If youadd outdoor use, make sure that the supply of greywater is sufficient to meet your projecteddemand. Table 2 shows:

how much money could be saved if the demand for toilet flushing in a typical 2.4 personhousehold was met entirely by treated greywater;

effect of moving to best practice low flush toilets also supplied by treated greywater.

Cost savings have been estimated using the charges made by two water and sewerage companiesrepresenting the higher and lower ends of the range of water charges in England and Wales.Payback periods are calculated by comparing the savings to an estimated initial investment.Demand data are based on consumption and frequency of use data from Assessing the Cost ofCompliance with the Code for Sustainable Homes(Environment Agency 2007).

The cost of greywater systems is variable, but 2,500 for purchase and 500 for installation (total;3,000) are conservative figures and suitable for a ballpark calculation based on an individualdomestic system. The cost of communal systems will be more variable. Installation costs could belower if incorporated into construction, but could be significantly higher in complex retrofitinstallations.

These calculations ignore maintenance and running costs, which will inevitably increase paybackperiods. These costs are excluded as they depend on the type of system and are not well known.

Where the requirement for outdoor water use is significant, savings could be greater than thoseindicated assuming the supply of greywater is sufficient to meet demand. At a flow rate of 9 litresper minute, a hosepipe can use 540 litres of water per hour. Where there is significant demand forgarden irrigation, which was previously met by mains water, savings could be significantly higherand payback periods shorter. For more information on how to reduce water use in the garden, seechapter 6 of our publication, Conserving Water in Buildings.

17

17http://www.environment-agency.gov.uk/commondata/acrobat/cwb_ch6_gardening_880746.pdf


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Table 2: Example cost savings from greywater systems in areas with different water charges

Low water/wastewatercharges*

High water/wastewatercharges**

Appliance

Standardtoilet

Low flushtoilet

Standardtoilet

Low flushtoilet

Litres per flush 6.0 4.5 6.0 4.5

Flushes/person/day 4.8 4.8 4.8 4.8

Number of occupants 2.4 2.4 2.4 2.4

Total flushes/day 11.5 11.5 11.5 11.5

Daily use (litres)*** 69.1 51.8 69.1 51.8

Annual water use (m3) 25.2 18.9 25.2 18.9

Unit cost of water supply and

wastewater treatment (/m3

) 1.40 1.40 4.00 4.00

Estimated cost savings fromgreywater (/year) 36.10 27.00 101.20 75.90

Cost of greywater system () 3,000 3,000 3,000 3,000

Payback (years) 83 111 30 40

* South West Water (2007-08 measured charges)http://www.southwestwater.co.uk/media/pdf/g/k/ApprovedCS2007_1.pdf** Thames Water (2007-08 measured charges)http://www.thameswateruk.co.uk/en_gb/Downloads/PDFs/leaflet07-08_Metered_charges.pdf*** Systems that use chemical disinfection may not be appropriate for garden irrigation as high disinfectantconcentrations can damage plants.

Because water charges vary across the country, a greywater system installed in an area with highwater charges such as south-west England will have a significantly shorter payback period than asimilar system (with similar usage) installed in an area with lower water charges. Charges tend toincrease year on year and this will decrease payback times.

As with everything mechanical, there is the risk of failure and a requirement for servicing. Given thelengthy payback periods, any significant maintenance or repair costs will have a major impact oncost savings.

There are also running costs to consider such as chemicals or energy for treatment and pumpingrespectively. Payback periods may be longer than the operational life of the system. Indeed theindividual who made the initial investment may have moved house before the payback is realised.

One way of making greywater systems more cost-effective is to use a communal system. Thisspreads the costs of installation, operation and maintenance and therefore allows a more intensive(expensive) treatment process. It also smoothes out supply and demand (by avoiding specificusage variations) and allows a formal maintenance and servicing contract to be set up. Energy usecould also be reduced by installing bigger, more efficient pumps and treatment processes. For allthese reasons, communal systems probably make more financial sense than individual systems.Unfortunately there is a lack of detailed case studies on communal greywater systems.

A guide published by the Construction Industry Research & Information Association (CIRIA)provides basic advice on the use and development of model operation and maintenanceagreements for rainwater and greywater systems, together with simple guidance on theirincorporation into developments (CIRIA 2004). This guide can be purchased from the CIRIA

website.

18

18http://www.ciria.org/acatalog/C626.html


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Installation during construction makes systems more cost-effective; the costs of retrofitting can bevery high and the process disruptive. Many existing properties in England and Wales may also beunsuitable for greywater systems that require a large area to house them (e.g. AquaCycle 900).

Although the cost-effectiveness of greywater systems is variable, this option is likely to become

more attractive in future due to:

increasing cost of water; the increasing popularity of greywater systems; decreasing costs of greywater systems.

The economics of communal systems could potentially be significantly more favourable and theremay be potential for the deployment of greywater systems at this scale.


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6. EnergyThe seemingly ludicrous practice of using water treated to drinking quality to flush the toilet is part

of the appeal of greywater recycling systems. Surely treating water to drinking water quality andthen flushing it down the toilet is a huge waste of energy and unnecessarily adds to carbonemissions?

But due to efficiencies of scale, the process of treating, supplying and distributing mains water ismore efficient than you might think. During 2006/2007, for example, it required 559 kWh ofelectricity to abstract, treat and supply the average mega litre (Ml - one million litres) of water tohouseholds in the UK (WaterUK 2007). This is equivalent to 0.559 kWh/m

3(1 m

3= 1,000 litres). To

take this water away and treat it used a further 756 kWh/Ml or 0.756 kWh/m3.

In general, the higher the standard of water quality required the more energy intensive the process.Therefore using cooled bath water to irrigate the garden in place of mains water will save energy.But using a bio-mechanical system to treat greywater will generally use more energy than if mains

water was used instead.

Table 3 compares energy consumption when using mains water and treated greywater for toiletflushing in a typical household. It makes the same usage assumptions as those in chapter 5.

The greywater system considered in Table 3 is the WME-4 (see section 2.5) for which themanufacturers literature

19quotes energy use as 3.5 kWh/m

3. This system uses an intensive

process to achieve high quality water and therefore its power consumption will be higher than thatof simpler systems. Only the energy use of this system is considered here due to the lack of datafor other greywater treatment systems.

Table 3: Comparison of energy use from mains water and treated greywater*

Mains water** GreywaterAppliance

Standard toilet Low flush toilet Standard toilet Low flush toilet

Litres per flush 6.0 4.5 6.0 4.5

Flushes/person/day 4.8 4.8 4.8 4.8

Number ofoccupants

2.4 2.4 2.4 2.4

Total flushes/day 11.5 11.5 11.5 11.5

Daily use (litres) 69.1 51.8 69.1 51.8

Annual water use forappliance (m3) 25.2 18.9 25.2 18.9

Energy per cubicmetre

1.3 1.3 3.5 3.5

Energy used (kWh) 33.2 24.9 88.3 66.2

* Energy use includes supply and treatment for mains water and only the energy used internally in thetreatment of greywater.** Energy data from WaterUK (2007).

Table 3 shows that using greywater to flush toilets may not be an energy (and therefore carbon)saving technology. While substituting mains water with treated greywater for toilet flushing willinevitably save water, it will have other trade-offs which should be considered on an individual

basis.

19http://www.aqua-lity.co.uk/en/products/control_units/aqua_recycling_control_wme_4/index.html


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However, the amount of energy used by even the most complex greywater systems is smallcompared with the energy used to heat water in the home. Heating water for domestic uses, suchas showering and bathing currently contributes about 5 per cent of the UKs annual greenhousegas emissions. That is seven times more than the contribution from the water industry.

20

If you are primarily interested in saving energy, you should target excessive use of heated water.Many water efficiency measures such as aerating shower heads (which use less water but give theillusion of high flow) are simple and cheap to install and use. These will save a significant amountof heated water and therefore energy.

Although greywater and rainwater can be used either at a community or individual household levelto meet non-potable water needs, simple water efficiency measures should be considered first.Water recycling and reuse involves trade-offs between water use, energy use (for high-techsolutions) and land use (for low-tech solutions). These must be balanced against water savings toensure a sensible approach to water management (Environment Agency 2006). As technologiesimprove and mains water becomes more expensive, this balance may well shift in favour ofgreywater recycling and rainwater harvesting.

20http://www.defra.gov.uk/corporate/ministers/speeches/ian-pearson/ip070426.htm


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7. Conclusions Greywater systems may become more common in the UK driven by:

Code for Sustainable Homes; increasing cost of water; increasing awareness of the importance of conserving water.

Greywater systems vary in complexity from simple systems with minimal treatment andstorage to more complex systems that can treat greywater to a standard sufficient to allowextended storage. While some simple systems have clear benefits, more complex oneshave other trade-offs such as energy use (for high-tech options) and space (for intensivebiological options).

There are currently no water quality standards in place for treated greywater. However,there are guidelines based on the Bathing Waters Directives which relate to the intendeduse of the recycled water.

Even the most intensive greywater treatment will not generally produce water suitable fordrinking. It is therefore important that:

the water fittings regulations are followed to avoid contamination of the mains watersupply;

WRAS guidance on pipe labelling is followed to avoid cross connections.

The reliability of greywater systems remains largely unproven and maintenance costs areuncertain.

Greywater systems can have lengthy payback periods. These vary depending on demandfor non-potable water and local water charges. Payback periods may be shorter in futureas systems become cheaper and water charges increase.

It is better to install greywater systems during construction or refurbishment, as retrofittingis costly and disruptive.

Communal systems avoid many of the issues associated with individual installations. Theycan offer improved supply/demand balance, superior water quality, superior systemreliability (through better maintenance) and more reliable cost savings. However, publicacceptability and an increased risk of cross connections need to be taken into account.

Greywater can provide a more reliable and consistent supply of non-potable water thanrainwater harvesting.

Greywater recycling does not necessarily save energy. To save energy, it is better to focuson water efficiency and specifically on reducing the volume of hot water used. Usinguntreated greywater in place of mains water for garden irrigation saves energy and water,but it must not be stored for long.

Remember: reduce, reuse, recycle. When looking to reduce water consumption, start withsimple water efficiency measures.


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8. References Centre for the Study of the Built Environment (CSBE), 2003 Greywater Reuse in Other

Countries and its Applicability to Jordan. Amman: CSBE. Available from:http://www.csbe.org/graywater/report/report_final.pdf [Accessed 14 April 2008].

CIRIA, 2001 Rainwater and Greywater Use in Buildings: Project Results From TheBuildings that Save Water Project. Best Practice Guidance. C539. London: CIRIA.

CIRIA, 2004 Model Agreements for Sustainable Water Management Systems. ModelAgreement for Rainwater and Greywater Use Systems. C626. London: CIRIA.

CRC Water Quality and Treatment, 2003 Setback for Netherlands Dual SuppliesHealthStream, Issue 30, 5, June 2003. Available from:http://www.waterquality.crc.org.au/hs/pdf/HS30.pdf [Accessed 14 April 2008].

Environment Agency, 2006 Water Related Infrastructure for Sustainable Communities.Technological Options and Scenarios for Infrastructure Systems. Science ReportSC050025. Bristol: Environment Agency.

Environment Agency, 2007 Assessing the Cost of Compliance with the Code forSustainable Homes. Bristol: Environment Agency.

Hills S, Birks R, Diaper C and Jeffrey P, 2002 An Evaluation of Single-house GreywaterRecycling Systems. Reading: Thames Water Utilities. Available from:http://www.thameswater.co.uk/en_gb/Downloads/PDFs/FINAL_102-Hills_S.pdf [Accessed14 April 2008],

Jeffrey P, 2002 Public attitudes to in-house water recycling in England and Wales, Journalof the Chartered Institution of Water and Environmental Management, 16, 214-217.

Market Transformation Programme (MTP), 2007 Rainwater and Grey Water: Review ofWater Quality Standards and Recommendations for the UK.

Ministry of Agriculture, Natural Resources & Environment (MOA), 2002 Use andConservation of Water in Cyprus. Nicosia, Cyprus: Ministry of Agriculture, NaturalResources & Environment, Water Development Department. Available from:http://www.cyprus.gov.cy/moa/wdd/Wdd.nsf/booklets_en/A64990F3A94D8472C2256E850049E412/$file/pages%201-19%20(0.84MB).pdf [Accessed 14 April 2008].

National Water Demand Management Centre (NWDMC), 2000 A Study of Domestic

Greywater Recycling. Worthing: Environment Agency.

Ofwat, 2005 International Comparison of Water and Sewerage Service. London: Ofwat.

Ofwat, 2007 Security of Supply 2006-07 Report. London: Ofwat.

Po M, Kaercher J D and Nancarrow B E, 2003 Literature Review of Factors InfluencingPublic Perceptions of Water Reuse. CSIRO Land and Water, Technical Report 54/03.Available from: http://www.clw.csiro.au/publications/technical2003/tr54-03.pdf [Accessed14 April 2008].

WaterUK, 2007 Sustainability Indicators 2006/07: UK water industry sustainabilityindicators. London: WaterUK. Available from:

http://www.water.org.uk/home/policy/reports/sustainability/sustindicators06-07 [Accessed14 April 2008].


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Water Regulations Advisory Scheme (WRAS), 1999 Marking and Identification of Pipeworkfor Reclaimed (Greywater) Systems. WRAS Information and Guidance Note No 9-02-05.Gwent: WRAS. Available from: http://www.wras.co.uk/PDF_Files/IGN%209-02-05%20Marking.pdf [Accessed 14 April 2008].


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9. Glossary of termsAA air gap The inlet supply of potable water to any cistern containing rainwater, greywater

or reclaimed water must be protected by an air gap suitable for protectionagainst a Class 5 risk [see Water Supply (Water Fittings) Regulations 1999].

Cistern A fixed container for holding water to be used as toilet flush water.

Coliforms Bacteria found in the intestines, faeces, nutrient-rich waters, soil and decayingplant matter.

Cross-contamination Pipes carrying non-potable water connected to pipes carrying mains water.

Escherichia coli A member of the coliform group of bacteria. Unlike total coliforms, E. coliarealmost exclusively of faecal origin. The presence of E. coliis therefore a strongindicator of faecal contamination.

Enterococci A group of bacteria commonly found in the bowel of normal healthy individuals.Another strong indicator of faecal contamination.

Greywater Wastewater from showers, baths, washbasins, washing machines and kitchensinks.

Greywater reuse Utilising untreated greywater for purposes that do not require potable waterquality.

Greywater recycling Utilising treated greywater for purposes that do not require potable waterquality.

Legionella The bacterium, Legionella pneumophila, can cause legionnaires' disease (lunginfection) in humans.

Non-potable water Water that is not treated to sufficient quality for drinking.

Potable water/mainswater

Water that is treated to sufficient quality for drinking.


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10. List of abbreviationsBOD biochemical oxygen demand

BSRIA Building Services Research and Information Association

BTSW Buildings That Save Water [project]

CIRIA Construction Industry Research and Information Association

Defra Department for Environment, Food and Rural Affairs

Ml megalitres

MTP Market Transformation Programme

UV ultraviolet

WRAS Water Regulations Advisory Scheme


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