Contributions Relating to Rainwater Harvesting

8/9/2019 Contributions Relating to Rainwater Harvesting

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This is one of 126 contributing papers to the World Commission on Dams. It reflects solely the views

of its authors. The views, conclusions, and recommendations are not intended to represent the views of

the Commission. The views of the Commission are laid out in the Commission's final report "Dams and

Development: A New Framework for Decision-Making".

Contributing Paper

Contributions Relating toRainwater Harvesting

John Gould

Independent Expert, New Zealand

Prepared for Thematic Review IV.3:Assessment of Water Supply Options

For further information see http://www.dams.org/

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Assessment of Water Supply Options

Contributions relating to rainwater harvesting

for sections 2, 3.2, 4.1, 4.3, 5, 6 and 7

John Gould

24th Oct. 1999(1st Draft)

Edited Version sent 27th

Oct. 1999

Please find attached my preliminary input to this review. Since I am not sure how you wish

to incorporate this information I have included most of the case study material in separate

boxes so that if it was not possible to include it all it can easily be dropped. I have

numbered the boxes and refer to them in the text so if any are dropped or moved or their

numbering changed these references will have to be amended.

The section numbers used in this draft are those proposed in the Revised Draft Outline

proposed on Oct. 20th 1999.

N.B. Suggested changes to section headings for 4.1 and 4.3.2

Please let me know if you need any additional material or any of these sections expanded

or developed.

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Contents

Inputs on Rainwater Harvesting for the following Sections:-

2. The Nature of The Debate And Purpose of this Review- Challenging Conventional Approaches to Water Supply Provision

3.2 Alternative and Indigenous Technologies

3.2.1 Rainwater Harvesting

3.2.2 Roof Catchment Supplies

3.2.3 Rainwater Harvesting in Rural Areas

3.2.4 Rainwater Harvesting in Urban Areas

4. Demand Side Options and Associated Issues4.1 Current Strategies

A. Demand Management

- Community control/involvement

- Public-private initiatives

B. Technological Advances

C. Raising Public Awareness/Public Education

4.3.2 The Influence of Demand/Supply Side Options on Demand Forecasts

5. Trends in Project Financing and Project Analysis

6. Adequacy of the Institutions and Processes for Assessing Options

7 Recommendations for World Commission on Dams

References

Supplementary information which some of which could be incorporated in the text or

included as Annexes or as Text Boxes ??

Rural Case studies

Box 1 1-2-1 Rainwater Project in Gansu Province, China

Box 2 Thai Rainwater Jar Construction Programme

Box 3 Experiences with Project Funding in Kenya

Box 4 Rainwater Harvesting in Sri Lanka

Urban Case Studies

Box 5 Promotion of Rainwater Collection in Tokyo

Box 6 Subsidies for Household Rainwater Systems in Germany

Box 7 Rainwater Survey in Squatter Settlements of Tegucigalpa, Honduras

General Background Information

Box 8 The Growing Global Interest in Rainwater Harvesting

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Section 2

The Nature of the Debate and Purpose of this Review

- Challenging Conventional Approaches To Water Supply Provision

In the 1980's the world community embarked on the worthy challenge of endeavouring to provideaccess to clean water and sanitation to all by 1990. Even at the start of the International DrinkingWater Supply and Sanitation (IDWSS) Decade (1981-1990) during which hundreds of millions ofpeople were supplied with improved water supplies, it was clear that the goal of "water for all" wasunattainable. This was due mainly to a lack of political will both in the North and the South. Anothermajor obstacle was an unrealistic faith in modern technologies and implementation strategies whichin the event proved inappropriate in many rural and peri-urban communities of the South. Despite theefforts made during and since the Decade, well over 1 billion people still lack access to convenientand safe water supplies and many more have no proper sanitation. At the same time, another billion

people have access to both abundant water and the fruits of irrigation, both of which are delivered tothem at affordable and often highly subsidised prices. When the economic incentives and subsidiesare available, supplying water even to desert cities such as Phoenix, Arizona is possible, although inthese marginal environments such ventures are usually inherently unsustainable (Postel 1992).

The challenge of providing water and sanitation for all is clearly one for which a solution is longoverdue. Hundreds of billions of dollars have been spent on water resource development projects indeveloping countries in the past half century yet few of the benefits of these projects have beendirected to those facing the greatest water needs. There are numerous reasons for the failure of pastefforts to provide universal access to clean water including population growth, war, corruption and aninsufficient commitment on the part of governments around the world to seriously address the

infrastructural and social needs of either the rural or urban poor. While many new water supplieshave been built, a significant number have failed due to poor management and inadequatemaintenance, as well as over-exploitation, pollution or salinization of water sources. While theintroduction of new technology has improved water provision in some places, in others especially inremoter regions of developing countries, it has often proved to be unsustainable. The reasons forproject failures have invariably been because the technology and/or approach used for itsimplementation have been technically, economically, socially, or environmentally inappropriate. Atvillage level, past experience has shown that water systems which are dependent on external sourcesof fuel, spare parts, or expertise for maintenance and repair are less likely to be sustainable than thosedependent only on local inputs unless well developed and reliable systems are in place for providingany external requirements.

There has been a tendency in many developing countries to equate improved water supplies withmodern technologies such as large concrete dams, motorised pumps, pipeline systems which haveoften proved inappropriate particularly in poor rural settings. An unfortunate corollary to this hasbeen that many traditional technologies, such as the quanat systems in Iran, tried and tested over thecenturies and both sustainable and appropriate to the needs of the local community have beenoverlooked in favour of more modern approaches.

Rainwater harvesting systems have often been grouped into this same category of traditionaltechnologies and have been ignored in favour of modern and supposedly better alternatives. In theThar desert in India, many communities have depended for centuries on a variety of traditionalrainwater harvesting technologies. These include tankas, simple clay lined reservoirs, kundis, covered

tankas with compacted mud catchment areas and khadins, low walls diverting runoff from hillsidesonto crops. While most of these khadins are still being used for runoff farming, many tankas and

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kundis have been abandoned since the arrival of modern piped water schemes. Ironically, a study bythe Centre for Science and the Environment (CSE) during the 1987 drought indicated that while manyon the new schemes based on tube well sources dried up, villages still depending on the traditionaltechnologies still had water to drink (Agarwal & Narain 1989). A return to the use of traditionalrainwater harvesting technologies has subsequently been actively promoted by the CSE not only in

the arid states of Rajistan and Gujarat but throughout the country (Agarwal & Narain 1997).

Considering that world-wide there are hundreds of millions of people who depend on rainwatersupplies for part or all of their domestic water needs, it is surprising how little attention thetechnology has been afforded. For example, in the comprehensive and authoritative text Water inCrisis: A Guide to the World's Fresh Water Resources edited by Gleick, P. 1993: rainwaterharvesting only warrants a single mention. It is nevertheless significant that this reference is made inthe section on Water in the 21st Century. Here, in reference to the revival of rainwater harvestingtechniques developed in the Negev desert over 2 000 years ago and now being applied in many partsof Africa, Gleick writes:

"We have much to re-learn from traditional water management experience. Small-scale

indigenous systems can often be more effective at meeting community needs without thelarge, unexpected impacts of large-scale developments, and community-level participation in

water supply development and management often leads to other economical, educational, or

health benefits as well ..

... Unfortunately, such traditional approaches are often ignored by the international

development community and governments. They are excluded from surveys of water systems,

they do not get investment credits from international development programs, they are denied

the support of information and educational services, and they lack the glamour and high

profile of big projects. ..."

Several other analysts of the growing global water crisis have also proposed that greater credence

needs to be given to traditional solutions such as rainwater harvesting, (Clarke, 1991; Postel, 1992;Pearce, 1992; Agarwal & Narain 1997).

Since traditional water supply technologies have in most cases been able to meet the needs of localpopulations for many centuries, the systems are clearly sustainable. Ignoring this ancient wisdom andreplacing traditional approaches entirely with technologies and approaches just a few decades old,which are foreign to local communities would seem unwise. Major rural water supply initiatives inboth Gansu, China, and Northeast Thailand have clearly demonstrated that the traditional rainwaterharvesting technologies can be upgraded and improved in order to provide affordable and sustainablesupplies (Box 1 and 2). These and the examples cited from Kenya and Sri Lanka (Box 3 and 4)support the notion that roof catchment systems could play an important role in the provision ofhousehold level water supplies in many developing countries in the coming decades.

The consequences of failure to urgently provide at least the vast majority of those in rural areas withsatisfactory access to clean water could be extremely far reaching. Without convenient watersupplies, rural areas become even less attractive places in which to reside and the already rapid driftto the cities could accelerate putting even more pressure on the urban environment and its alreadyover stretched water resources.

Alternative and Indigenous Technologies

3.2.1 Rainwater harvesting

Rainwater harvesting is a general term which describes the small scale concentration, collection,storage, and use of rainwater runoff for both domestic and agricultural purposes. In relation to

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domestic water supply, roof catchment systems are by far the most common form of rainwaterharvesting technique used, although in many developing countries rainwater runoff is also collectedfrom ground or rock surfaces (Gould and Nissen-Petersen 1999). Rainwater collection is an ancientpractice which is still widely used, yet despite its long history the technology remains greatly under-utilised. If fully developed rainwater utilization could provide an important sustainable and

environmentally benign water source for supplementing other water supply options in a wide varietyof circumstances.

Despite having some clear advantages over other sources, rainwater use has frequently been rejectedon the grounds of its limited capacity or due to water quality concerns. This is unfortunate as inmany cases some simple upgrading and the integrated use of rainwater collection with othertechnologies is all that is required to obtain a cost effective and reliable water supply solution. Thiswas the approach adopted in the 1-2-1 project in Gansu Province China, which during 1995-1996provided household rainwater supplies to more than a million people (Zhu & Liu 1998) see Box 1.

The unequivocal success of the Thai jar programme also illustrates how a traditional technology canbe adapted, upgraded, and widely replicated in order to meet domestic water requirements at a

regional scale (Box 2). This project developed and upgraded the traditional practice of usingearthenware jars with volumes of up to 200 litres for rainwater storage. This was done by developinga simple affordable ferrocement jar design (1-2m

3) which could be easily constructed by

householders themselves with the assistance of a trained technician. Consequently, the jars quicklybecame popular and were widely adopted. Within a period of about six years (1985-1991), mosthouseholds in Northeast Thailand acquired at least one rainwater jar and in total more than 10 millionwere constructed. The result of this was that Thailand was one of the few countries to makesignificant strides towards achieving the goals of the IDWSS Decade with respect to water supplyprovision.

It is interesting to contrast the situation in Northeast Thailand with that in parts of rural South Africa.

In the densely populated provinces of Mpumalanga and Natal along the east coast of the country,millions of people still lack access to piped water in their homes. Although water provision has beenimproving at village level since the election of the new democratic government in 1994, for mosthouseholds domestic water is still collected from a communal tap. Except in the smaller and remotervillages most people now live in homes with tiled or corrugated iron roofs and it is very common tosee small makeshift storage vessels usually 200 litre oil drums or plastic containers under the eaves ofhouses. Despite an active campaign to promote improved rural water provision and waterconservation in recent years by government and NGOs, no systematic attempt has yet been made toupgrade these simple existing rainwater systems e.g. by replacing the oil drums with appropriatelysized and constructed catchment tanks and improved guttering. Unfortunately, the situation prevailingin South Africa is more typical of what has been occurring in most developing countries during thepast 20 years than the experience in Thailand. Nevertheless, some developing countries including

China, Kenya ,and Sri Lanka (Box 1, 3 and 4) have followed the Thai example to a lesser degree andhere a steady growth in the use of rainwater harvesting for domestic supplies has been evident (Zhu& Liu, 1998; Gould & Nissen-Petersen, 1999; LRWHF 1999).

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3.2.2 Roof Catchment Supplies

The collection of rainwater runoff from household roofs is the most common form of rainwaterharvesting and attractive to householders from a several of points of view. First, for an existingdwelling the catchment area is available at no additional cost. Second, contamination of rainwaterrunoff from a well constructed and properly maintained roof is small compared with that from aground catchment system. Third, roof catchments provide a water supply at the point of consumption.Finally, since the household owns the system and is solely responsible for it maintenance is likely tobe undertaken regularly, ensuring effective long-term system operation. Experience from around theworld has shown that where rainwater tanks at schools, churches etc. are shared communally thereoperation and maintenance is often neglected. In more arid climates, household roof areas may not besufficiently large to make investments in larger storage tanks needed for year round supplyeconomically viable. In Kenya large surface tanks and many 90m

3hemi-spherical subsurface

ferrocement water tanks have been constructed at hundreds of primary schools to provide potablewater at schools previously adversely affected water shortages, (Gould & Nissen-Petersen 1999).

Inspection of a global rainfall map will reveal that in much of South and Southeast Asia, Central and

West Africa, the Northeast half of South America, Central America mean annual rainfall exceeds oris close to 1 000 mm. This is significant as not only do, these regions contain over two-thirds of theplanets population, but they include the regions where many of those lacking adequate water suppliescurrently reside. In a semi-humid climate with a mean year round rainfall of 1 000mm, even a modestsized 50m2 roof, can potentially yield up to 40m3 of water annually, equivalent to more than 100litres of water per day. Depending on the rainfall variability a tank of 2-4m3 would probably berequired to provide this level of household supply with a reasonable level of reliability. While in asemi-arid climate, with seasonal mean rainfall of 500mm/a, even from a modest sized 50m2 roof,potentially 20m3 of water could be collected which with sufficient storage could supply more than 50litres of water per day to the household. This would, however, require a storage capacity of perhaps5-10m3 depending on the degree of rainfall variability to ensure a high reliability of supply. While

the costs of roofwater harvesting increases in drier, more seasonal climates due to the largercatchment area and storage volume requirements, so do the costs of other alternatives.

In climates subject to drought it is not uncommon to find that governments are forced to deliveremergency water supplies by truck if boreholes, reservoirs, or other water sources dry up. Truckingwater can be extremely expensive and in situations where such supplies are used from time to time,there may often be a justification for installing rainwater tanks on economic grounds alone.Rainwater can be stored for long periods of time provided that light, insects, animals, and organicmatter are excluded from the tank.

In more humid climates, especially where year round rainfall is available, a large proportion ofhousehold water demand can normally be met with only a relatively small storage tank. This was

clearly demonstrated by recent analysis of the performance of household roof catchment systems intwo villages in Uganda (Thomas 1998). Mbarara and Kyenjoro are subject to two rainy seasons andreceive mean annual rainfall totals of 900mm and 1400mm, respectively. The analysis revealed thatin both cases a storage capacity equivalent to just a four days of household consumption couldprovide a useful domestic water source for at least half of the year. In the light of these findings it iseasy to explain the enormous popularity shown for the relatively small (1-2m

3) rainwater jars in

Northeast Thailand where the rainfall conditions and large roof areas make rainwater harvesting evenmore favourable. Clearly, in regions where rainfall conditions are conducive to roofwater harvestingrelatively small investments in storage tanks can produce significant impacts.

3.2.3 Rainwater Harvesting in Rural Areas

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The failure of both traditional and improved communal systems to provide adequate water supplies inrural areas is an important reason why household rainwater collection is gaining popularity in manydeveloping countries e.g. China, Thailand, Kenya, and Sri Lanka. Probably the single most importantfactor, however, is the shift away from the use of traditional roof construction techniques involvinggrass/palm thatch and dried mud in favour of modern impervious roofing materials such as fired clay

tiles and corrugated iron. This improvement has resulted in households possessing appropriatecatchment surfaces which only require a tank and simple gutter in order to provide a rainwatersupply. The development of appropriate and affordable designs such as those for the in situ concreteand ferrocement tanks in several countries has further encouraged the spread of rainwater systems(Gould and Nissen-Petersen 1999).

The benefits of rainwater collection in the rural context of the developing world is particularlysignificant for women due to the great amount of both time and energy which they can save. In manyparts of rural Africa and Asia women still spend hours each day collecting water. In some cases andespecially in dry periods this will involve treks to polluted sources several kilometres from peopleshomes. Under such circumstances the acquisition of a household rainwater tank represents animmediate and dramatic improvement in quality of life. For example, even a modest 2m3 Thai

rainwater jar can store the equivalent of one hundred 20 litre water buckets weighing 2 000kg (twometric tons) which without the tank the householders, usually the women and children, would havehad to collect and carry some distance. Given this reality, even if rainwater supplies cannot meet thetotal household requirements any water they can provide represents a substantial benefit to thehousehold.

Increasingly, rural women are collecting improved water supplies from communal tap stands nowfound in most larger and many smaller villages in the South. Nevertheless, even where these areavailable women may still have to walk several hundred metres or more to collect water andsometimes queue for long periods to fill each bucket. Breakdowns and the drying up of supplies indrought periods are also common occurrences in some regions. Given such circumstances, the

introduction of rainwater tanks may be appropriate even when communal taps are available.

The provision of water at the point of consumption from rainwater tanks provides a range ofimmediate positive social impacts on health, family welfare and domestic productivity. This resultswhen time saved in water collection is utilised elsewhere. Some of the time saved maybe used forproductive activities such as agriculture with clearly tangible and easily valued economic benefits.More time can also be spent on activities such as child rearing when women have time freed up fromthe daily chore of water collection. The value of such benefits to family livelihood and well-being aredifficult to assess and are rarely appropriately costed.

The use of rainwater harvesting for domestic water supplies is also relevant in the rural areas of manymore developed countries e.g. Australia, New Zealand and the USA.. In Australia rainwater use has

always been practised by farming households in the outback. Currently, over 1 million people stilldepend on rainwater for all or part of their domestic water needs. Formal guidelines with advice tohouseholders on best practice regarding rainwater tank use were recently produced (Cunliffe 1998).These guidelines include advice on protecting water quality, water treatment, maintenance and repairand tank sizing including tables to assist with calculations. In South Australia where rainwatercollection is widely practised even in urban areas such as Adelaide and in much of the arid interior ofthe continent and especially Western Australia large mechanically graded surface catchments oftenmany hectares in area are used to collect water for livestock and small settlement supplies.

Rainwater harvesting is widely used around the world for purposes other than domestic water supply.Rainwater runoff is often be diverted onto plots or into ditches or ponds to provide water for

gardening, tree nurseries, aquaculture, livestock watering and numerous other purposes. The largescale harvesting of rainwater both using within field micro-catchment systems and external hillside

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catchments to divert runoff onto cultivated plots is widely used in many semi-arid environments foragriculture (Pacey & Cullis 1986). Apart from the agricultural applications for crop production,rainwater harvesting and the related techniques such as floodwater harvesting and spate irrigation, arealso widely used to recharge groundwater. These ancient techniques are also currently enjoying arevival in some parts of the world such as Iran (Aminipouri & Ghoddousi 1997). The implications of

the widespread replication of these methods on reducing the demand for irrigation water, thesustainability of groundwater supplies as well as their impact (both positive and negative) on existingsurface water sources could be far reaching. In more densely populated arid environments thediversion of surface runoff and its storage in the soil may also help to reduce erosion problems.

3.2.4 Rainwater Harvesting in Urban Areas

Traditionally most rainwater harvesting has been most commonly associated with remote rural areasor those lacking alternative water sources, e.g. coral islands. Several global trends are making themore general use of rainwater utilization in future more likely especially in large cities. The mostsignificant of these trends is urbanisation especially in developing countries. There has already been

an almost doubling of the urban population in the South since 1960. By 2030 it is expected that therewill be nearly 5 billion people living in urban areas world-wide of which more than 75% will be inAsia, Africa, and Latin America (UNFPA 1999). Urban development is already putting considerablestrains on existing water resources which are struggling to keep pace with steadily rising demands.The continuing over-exploitation and pollution of many existing water sources is leading to agrowing interest in alternatives such as rainwater catchment systems as supplementary water sourceswith multi-purpose functions.

Japan and Germany are both leading the way with respect to developing models for future patterns ofrainwater utilization in cities (Murase, 1994; Knig, 1998). Flooding and problems associated withground subsidence related to groundwater extraction are currently faced by several large Asian

megacities including Tokyo, Osaka, Shanghai and Bangkok and are fuelling this interest in rainwaterutilization (Box 5). In Germany there are even deliberate attempts to encourage householders tocollect rainwater runoff and divert any unneeded surplus to recharge groundwater (Box 6).

The utilization of rainwater in an urban context provides several potentially beneficial functions withrespect to the following:

flood control - by greatly reducing urban runoff; stormwater drainage - by reducing the size and scale of infrastructure requirements; firefighting and disaster relief - by providing independent household reservoirs; water conservation - as less water is required from other sources; reduced groundwater exploitation and subsidence - as less groundwater is required; financial savings - where rainwater can be used in place of water purchased from water

vendors often charging up to 10-50 times the official water tariff.

Potentially perhaps the most significant impact of rainwater harvesting technology in the urbancontext may be in providing water supplies to hundreds of millions on unserved residents on theperipheries of the new megacities of the South such as Tegucigalpa in Honduras (Box 7).

Predictions regarding Global warming could have a major effect in significantly increasing waterdemand in many cities. At the same time increased evaporation from reservoirs and reduced riverflows in some areas may decrease the available surface water supplies. A greater uncertaintyregarding yields from major reservoirs and well fields is likely to make investments in thediversification of water sources, better water management and water conservation even more prudent

in future. Increased climatic variability and the greater frequencies of droughts and floods possible inmany areas will also make the role of rainwater harvesting systems even more important as sources of

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supplementary, back-up, or emergency water supply. This will particularly be the case in areas whereincreasing pressure is put on existing water resources.

Many large cities around the world already face periodic water shortages and millions of urbanresidents including those connected to reticulated systems are forced to buy water from vendors or

retailers and often to ration water supplies. As cities continue to grow in the future such problems arelikely to become increasingly common. Since cities comprise of numerous impervious surfacesdesigned to encourage rainwater runoff the scope for rainwater collection is substantial. Atmosphericpollution remains a major constraint as it contaminates both the rainwater and catchment surfacesmaking rainwater unsuitable for drinking in many cities around the world. Nevertheless, rainwatercan still be used for non-potable uses such as toilet flushing, clothes washing and gardening (Box 6).Furthermore, great use of rainwater in urban areas could in future significantly strengthen the lobbyto clean up the urban atmosphere entirely.

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{ Some comments relating to rainwater harvesting projects}

Section 4

Demand side option and associated issuesAlthough strictly speaking a rainwater harvesting technology itself is a supply side option which canbe used to help reduce pressure on other conventional water sources. In many respects the operationand management of a roof water system can act as an important demonstration of the renewable yetfinite nature of water resources and the need to use water in a rational and sparing way. Rainwatercatchment systems can therefore often provide a central focus for any integrated water conservationcampaign in which both demand and supply side approaches are adopted. The publics level ofawareness regarding the importance of using water resources sparingly and rationing usage in timesof drought will be greatly enhanced if they have first-hand experience of managing their ownrainwater supply.

4.1 Current strategies

4.1.1 Demand Management

- Community control / involvementJust as community participation and control is essential to the successful implementation, operationand maintenance of any rainwater tank project, it is equally important with respect to any effort toencourage demand management. Ultimately demand management strategies are unlikely to succeedwithout strict individual self-discipline and community control / policing with respect to anydirectives or preferably recommendations agreed by the community themselves regarding efforts to

promote water conservation.

- Public-private initiativesThere is some evidence that combined public-private sector approaches for rainwater harvestinginitiatives can work effectively in certain circumstances, e.g. the Thai jar programme (Box 2). Therole of the private sector for funding programmes in the poorest regions such as Africa and SouthAsia where most of the unserved communities reside should nevertheless be viewed with somecaution. Despite much rhetoric at the World Bank about the role of the private sector in communitywater supply and sanitation, very little of its investment sector is directed to the poorest communitiesor the poorest regions, notably Africa and South Asia.

4.1.2 Technological advances

To gain the full benefit of a rainwater supply which is limited by the available rainfall, catchmentarea, and storage capacity it is generally appropriate to use the system in conjunction with watersaving technologies and practices. This is especially the case in arid environments where waterscarcity will be greatest particularly during the dry season and in drought periods. Technologicaladvances in tank construction techniques, such as the development of cheaper ferrocement watertank technology and especially the Thai jar have greatly assisted the rate at which rainwatercatchment systems have been adopted. Future innovations particularly with respect to the furtherdevelopment of low cost durable water tank designs could encourage an even faster spread of thetechnology.

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4.1.3 Raising public awareness / public education

Public awareness and education with respect to the importance of water conservation and thepotential role which rainwater harvesting can play is still at a very basic level in many parts of theworld. A significant proportion of householders who harvest rainwater could greatly improve the

performance of their systems through very small and inexpensive design changes such as ensuringthat runoff from the whole of the roof catchment area is being diverted towards the tank and not justpart of it.

4.3 Forecasting demand for water

4.3.2 The influence of demand and supply side options upon demandforecasts

In many cases rainwater harvesting projects are designed to provide a supply to consumers equivalentto some arbitrary minimum daily requirement, e.g. 40 litres / capita / day and sometimes currentusage rates are used without considering that these are based on water carried from a remote source.When water supplies are provided at the point of consumption there is a natural tendency for bothwater demand and usage rates to go up. This can create problems for rainwater systems designed onlyto meet a lower target demand as the tanks will run dry during drier periods, causing householders tobe find water elsewhere and often being forced to revert to their previous unsatisfactory watersources. This can lead to a loss in the credibility of the rainwater harvesting system and its capacity tomeet future water needs.

In situations where rainwater harvesting technology and water saving devices are used in conjunction

with conventional piped water supplies substantial reductions in water demand should be possible. Insome instances even where little user education or awareness exists substantial water savings andsignificant reductions in demand should be possible. For example, in accommodation units wheretoilets are flushed using water from a small rainwater tank and low flow shower heads are fittedsubstantial savings in overall water consumption should follow with little effort.

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Section 5

Trends in project financing and project analysisWith respect to household roof catchment systems the issue of affordability is a crucial one especiallywithin the context of the rural areas of the developing world. The cost of a rainwater tank couldtypically be equivalent to the household's total cash income for a year and such large outrightpayments are beyond the means of most households. This presents a major barrier preventingindividuals from installing roof catchment systems independently especially in more drier seasonalclimates where greater storage capacities are needed. For households in poorer communities, someform of financing mechanism preferably in combination with an appropriate subsidy will often be theonly possible way of acquiring a rainwater system.

Examples of some successful approaches to project financing such as the use of revolving funds in

Kenya and the provisions of subsidies in Germany are detailed in Boxes 3 and 6, respectively. Otherapproaches which have been used successfully elsewhere include linking household rainwaterharvesting initiatives to income generating projects, e.g. Philippines and Indonesia, where pairs ofyoung breeding goats and piglets have been included in a rainwater tank construction financingpackage. If the animals breed successfully, two of the young are returned to the donor, some areretained for breeding and some fattened up for sale to generate income for any loan repayment. Whilethis approach contains some risks if breeding is unsuccessful, when it works well it can help to makeprojects virtually self financing.

Individual household rainwater systems often seem expensive compared to development ofcommunal rural shallow well or protected spring water supplies. This is generally the case and if

good quality shallow groundwater or spring water are available rainwater collection may only beappropriate as a supplementary source. In the early 1980's much effort was directed into developingincreasingly low cost designs and while some of these were successful, others such as the bambooreinforced cement as a low-cost alternative to ferrocement failed to stand the test of time.

Although there are some notable exceptions, the development and spread of rainwater technology hasnot generally been strongly promoted by government water departments or most international donorswhose major funding has remained focused on conventional and large-scale developments, e.g. damconstruction and reticulated supplies. In terms of meeting the challenge of providing water supplies tothe billion plus people still unserved, this is significant as large dams are seldom built to meet theneeds of either the rural or urban poor. Furthermore, the communities most affected by major damand other water resource developments are rarely, if ever, fully engaged in project planning and

frequently barely consulted at all. In some cases, even where rainwater projects have been supportedby governments or donors, the communities affected have been little involved. This invariably leadsto project failures such as occurred in Kilifi, Kenya in the mid-1980's (Box 3).

Even when rainwater utilization is compared on an apparently equal basis with all other feasiblewater supply options, it is usually subject to an inadvertent negative bias. This is because the standardeconomic analysis used for determining the costs and benefits of major dam developments usuallyunder-estimate the full cost. For example, many externalities such as the natural ecological servicesprovided by a river prior to damming are seldom fully costed and sometimes ignored altogether.Another common omission is the cost of the eventual decommissioning of the dam. The use ofinappropriate market based rather than social based discount rates can also distort the true cost of a

project.

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In many situations the issue will not be one of whether rainwater harvesting should be considered as asubstitute for another water supply option, but how could its use as a supplementary water source beintegrated into a project to develop the most cost effective overall mix of technologies formaximising the benefits and reliability of the supplies.

Despite the high initial cost of developing roofwater supplies in rural areas, when compared with thelevel of spending on some major urban water supply developments even in relatively poorer regionssuch as Africa the costs seem modest. In Botswana, a recently completed 350km long North-SouthCarrier pipeline and new Letsibogo dam constructed almost exclusively for municipal water supplyfor the capital and a few other urban centres with a total population of less than 400,000 has costaround $250 million. This is more than $500 per capita. A similar level of investment in theconstruction of household rainwater harvesting systems could probably have provided domesticwater supplies albeit of lower quality and quantity to ten times as many people in scattered ruralareas. To take an even more extreme example one might consider weighing the benefits of spending$5 billion dollars on constructing a Man-made River Project in the Libyan Desert for irrigation withusing the funds to construct household roof tank systems and simple runoff farming plots andmicrocatchments for 20 million rural African families.

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Section 6

Adequacy of the Institutions and Processes for Assessing Options

In most countries, the potential use of rainwater harvesting along with a broad range of both supplyside and demand side technological and management options available for helping to ensure thatfuture water needs are met are still given at best only cursory consideration. In this respect the currentprocesses for assessing water supply options should be considered to be seriously inadequate.

The use of roofwater, stormwater, and several other potentially significant alternative water sourcessuch as the reuse of greywater and water conservation strategies including the installation of watersaving technologies which could have a significant impact on curbing water demand are stillfrequently not even considered during standard water planning exercises in many countries.

There seems no rational reason that rainwater harvesting and a range of less conventional optionsshould not warrant consideration for providing either a supplementary or total water supply alongwith all other available options. In many instances even where the exclusive use of rainwater tanksmay not be economic, the technology may prove to be a cost effective alternative during criticaldrought periods when conventional sources dry up or when there is a system breakdown.

In a few countries, the implications of developing water resources sustainability is beginning to leadto gradual changes in thinking and approach in some institutions although due to inertia and pressuresfrom commercial interests and consumers this is a slow process. Clearly there is a need for trainingand capacity building in most institutions dealing with water resource development to encouragebroader, long-term and enlightened thinking to ensure the implementation of technologies and

approaches which will address the fundamental challenge o the sector faces in the new century ofproviding adequate and sustainable water supplies to all.

Practitioners within existing government water ministries and departments as well as planners anddecision makers need to be encouraged to think laterally and consider a wider range of potentialsolutions to water provision including less conventional approaches such as rainwater harvesting. Ifthe predicted future problems of water scarcity are to be minimised a new approach to water resourceplanning is needed in which the starting point should be the starting point in any master plan shouldbe the size of the available water resource that can be supplied at an economic and sustainable level.A range of approaches including demand and supply side technology and management options,should then be considered adopted to see how best the demand and target supply can be tailored

together..

Slowly the implications of developing water resources within the new framework of sustainabledevelopment is leading changes and their is a gradual recognition around the world of thepossibilities for approaching the task in radically different way. This enlightened thinking still seemsto be limited to a minority of institutions and individuals but seems to be spreading. With respectrainwater harvesting some evidence of the growing interest in the technology is outlined in Box 8.

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Section 7

Recommendations for the World Commission on Dams

With respect to the use of rainwater harvesting for domestic water supply and its related functionsrelating to stormwater drainage the following recommendations are proposed:

when planning any water supply development project whether for urban or rural water provision,the option of rainwater collection and storage for meeting all or part of the water requirementsshould be given equal consideration alongside all other options.

the World Commission on Dams should undertake a major survey of existing and proposedrainwater utilization initiatives in both rural and urban contexts to evaluate their appropriatenessin a variety of contexts for both domestic water supply and multi-purpose objectives, e.g. flood

control, fire fighting and irrigation.

Other possible recommendations for consideration :

analysis of the costs and benefits of any project needs to be far broader than it has been in the pastand consider not only the direct economic, environmental and social impacts of any project butalso less obvious but far-reaching affects. These might include the impact of the development on"natural services", e.g. seasonal flood-plain agriculture downstream of a dam or the influence itmight have on developing capacity and self-reliance in a community through introducing new

skills such as in water tank construction.

the opportunity costs forfeited by investment in any given project need to be carefully consideredand realistic alternative scenarios for the use of the funds considered to aid comparative analysis.

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BOX 1

1-2-1 Rainwater Project in Gansu Province, China

Gansu Province lies on the loess plateau in central China and is one of the driest and poorest areas of

the country with annual per capita incomes of around US$70-80 in rural areas. Traditionally, peoplehave depended on rainwater as their main source of water supply, excavating 20m3 clay linedunderground cisterns in the loess soil for storing surface runoff. In dry years, however, these couldnot always provide sufficient water and people were forced to trek long distances to rivers or todepend on government water trucks. In 1995 the region suffered its worse drought in 60 years. Inresponse the Gansu Research Institute for Water Conservancy with the support of the ProvincialGovernment launched the 1-2-1 project which was based on test trials, demonstrations and pilotprojects carried out since 1988.

The 1-2-1 project was so named because each family was provided with 1 clay tiled roof catchmentarea, 2 upgraded cement water cellars and plastic sheeting for concentrating rainwater runoff on 1field. Traditional clay lined water cellars (Shuijiao) were upgraded by lining them with cement orconcrete and small metal pumps attached. Proper tiled roof catchments and cemented court yardsreplaced the bare earth catchments and strong plastic sheeting was placed over the rills on fields toconcentrate runoff onto crops. Some households also used spare plastic sheeting to constructtemporary greenhouses using wooden frames. A trench dug around these was used to collect anyrainwater for watering the vegetables being produced.

Using these simple, effective yet inexpensive approaches, the project assisted over 200,000 familiesin 1995-1996 and ensured that around 1 million people were provided not only with sufficient waterbut also with food and through the production of cash crops some limited income. For a total cost ofaround $12 million, half provided by the local government and half by community donations, therecipient families acquired upgraded water supplies and supplementary irrigation. The provision of

labour and locally available materials by the community ensured that the total implementation costfor the project amounted to just $12 per capita.

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BOX 2

Thai Rainwater Jar Construction Programme

The construction of over 10 million 1-2 cubic metre ferrocement jars for rainwater storage in

Thailand between 1985-1991 has demonstrated the potential and appropriateness of rainwatercatchment systems as a primary rural water supply technology. The unprecedented success of theprogramme was a result of several favourable factors all encouraging the rapid spread of thetechnology.

These included the following:

the existing tradition of household rainwater storage in small jars; the relatively high rainfall and existence of large impervious roofs at most households the

low price of cement and labour;

the availability of low cost skilled rural labour; the ongoing rapid rural economic development; the development of a durable and affordable tank design; the combination of a top down and bottom up approach; the combined public and private sector involvement; a willingness to adapt, modify and improve both the design and implementation strategies.Although national, regional and local governments sponsored the programme through rural jobcreation initiatives to the tune of $64 million and some financial support was provided by bothforeign and local donors, the recipients themselves contributed to most of the cost estimated atbetween $250-350 million. The price of 1.8 cubic metre jars sold by entrepreneurs fell to just $20making outright purchase affordable to most people and making the use of revolving fundsunnecessary. By the early 1990's, most households in Northeast Thailand a region previously doggedby inadequate rural water supplies, had year round access to clean water.

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BOX 3

Experiences with Project Funding in Kenya

i. Revolving funds

Women's projects in Nakuru and surrounding Districts: The use of revolving funds have beenwidely used in Kenya. In Nakuru and the surrounding districts both the Anglican and CatholicDiocese water programmes have successfully used this approach for many years and several thousand10-15m3 roof tanks have been financed this way mainly by women's groups. Normally the groupscomprise of between 10 and 30 women and monthly contributions of anything between $2 and $10will be agreed to depending on what group members can afford and provided there is sufficient tomeet the cost of building at least on tank. At the end of each month a lottery system is used to decideat whichhouseholds tanks will be constructed. All members of the group contribute labour and helpto collect locally available materials such as sand and stones. Other materials and skilled labour arepaid for out of the fund. Some donors have encouraged revolving fund initiatives by offering to payfor an additional tank for every one or two constructed.

Machakos in situ concrete tank programme: This long enduring tank construction project whichwas started in the late 1970's by the Catholic Diocese Development Office, is funded largely by thetank recipients through revolving funds. Initially a subsidy of one third of the tank cost was providedby the Diocese to promote the scheme but once the programme was established this subsidy wasdiscontinued. The support has since been limited to administration, the provision of new moulds, andsome free technical advice apart from which the project is virtually self-financing. Since its initiationover six thousand 4m3 - 13.5m3 tanks have been constructed using a simple method involvingpouring concrete between concentric corrugated iron ring moulds and reinforcing each section withbarbed wire as the concrete is poured.The success of the project has been largely due to:

the technical appropriateness of the technology in this context; the affordability of the tanks through the use of revolving funds;

the total involvement of the community; the long term nature of the project and good administration.

ii. Loan repayment schemes

Kilifi Resettlement Scheme Project: In the mid-1980's, there were some attempts to fund ruralrainwater tank projects through loan schemes. One such initiative was attempted in Kilifi District.The donor that conceived the project engaged the community in only limited consultation before theproject. Households were provided with high quality centrally made ferrocement tanks for which theysigned loan repayment contracts committing themselves to repay the cost of the tank plus 6.5%interest after a two year grace period. The householders were also expected to provide and erect theguttering needed for the tanks. Perhaps not surprisingly, the community who were unfamiliar with thetechnology installed insufficient guttering and were dissatisfied with the yields from the rainwatertanks. The concept of contract and repayable loans were also foreign to the recipients and fewrepayments on which the continuation of the project depended were ever made.

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BOX 4

Rainwater Harvesting in Sri Lanka

Sri Lanka receives abundant rainfall with mean annual totals ranging from 900mm and 6000mm with

an overall national mean of around 1900mm per year. Due to the availability of alternative watersources in the past, there is no long tradition of roofwater harvesting for domestic supply.Nevertheless, in many hilly areas lacking access to reliable wells or gravity fed piped supplies watercollection often involves a long trek to distant sources with a long uphill return walk carrying a fullcontainer.

Following a study conducted in 1995, the Community Water Supply and Sanitation Project (CWSSP)first undertook a demonstration and pilot project involving the construction of about one hundred5m3 roof tanks for household water supply. Two designs were developed a sub-surface brick tank anda surface ferrocement tank costing about $100 and $125, respectively. For an average sized roof of60m2 a household in the project area could expect a rainwater supply equivalent to between 150-200litres/day or even higher during the wettest part of the year. By the end of 1997 over 5000 grant

applications for tank construction had been approved by the CWSSP in Badulla and Matara Districtsand around 2800 tanks had already been constructed..

The Lanka Rainwater Harvesting Forum was established in 1996 to promote the application ofrainwater for domestic purposes throughout the country and to develop technology and establishguidelines for good rainwater harvesting practice..

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BOX 5

Promotion of Rainwater Collection in Tokyo

Until the early 1990s, the main focus for application of rainwater catchment systems for domestic

water supply was directed towards developing countries and in particular rural areas. Clearly thesewere the areas where water was in greatest need and where the impact of improvements could bringthe greatest benefit to individual lives. In 1994, however, the Tokyo International RainwaterUtilization Conference was hosted in Japan (Murase 1994). The significance of this conference isimportant as it represented a turning point in perceptions regarding the role, applications, andpotential for rainwater catchment system technologies world-wide. From 1994 onwards, there was agrowing recognition that rainwater collection could play a vital role in addressing many of the waterproblems faced by the rapidly growing megacities around the world, especially in Asia.

While the vision for the broader, long-term outcomes from the Tokyo International RainwaterUtilization Conference were global in nature, the specific focus of the conference was on thepotential benefits for large cities of utilising rainwater. Tokyo provided an interesting case study asthe city faced several water related problems.

Existing dams supplying the city were stretched to capacity and new dam and pipelinedevelopments faced increasing opposition from environmentalists and other affected groups;

Subsidence due to groundwater over-exploitation had left over 2 million people in some parts ofthe city living below sea level and seriously at risk from the impacts of a tsunami;

There was also a growing concern about the possible impact of flooding within the city and therisks associated with the worst case scenario of an earthquake and typhoon striking simultaneouslyand flood waters entering the subway system during the rush hour.

Such fears have generated considerable interest in all methods for disaster mitigation and they arenot unfounded.. In 1923 the Great Kanto Earthquake killed over 120,000 people in the city and most

of those who perished were victims of the firestorms which raged through the city. In Tokyo andelsewhere in Japan there has thus been much interest in the use of household water storage systemsto provide water for fire fighting purposes especially following an earthquake when pipe suppliesmight not be available. Such household reservoirs could also provide emergency domestic watersupplies in the period immediately following any major seismic event. Although rainwater is still notutilised much in Tokyo there has been some serious investigation into the potential role that rainwatercatchment systems could play in water supply, flood prevention, and disaster mitigation strategies. Anumber of interesting demonstration projects have also been developed to illustrate this potential. Atthe main sumo wrestling stadium, the Kokugikan, the rainwater runoff from the 8400m2 roof isdiverted into a 1000m3 basement tank for toilet flushing and cooling the building.

Calculations of the total rainwater runoff from the Tokyo area reveal that this is greater than the totalwater consumption of the metropolis which could theoretically become self-sufficient in water.

BOX 6

Subsidies for Household Rainwater Systems in Germany

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In Germany there is currently a growing interest in the promotion of household rainwater collectionparticularly at local government level. Due to serious industrial air pollution and strict regulationsregarding drinking water standards, household rainwater supplies are limited to non-potable uses suchas toilet flushing, clothes washing, and garden watering. In addition to reducing overall domesticwater demand, benefits from rainwater utilization include flood control and reduced stormwaterdrainage capacity requirements. When used in conjunction with a seepage well to return any overflowto the ground, the systems also enhance groundwater recharge. Most household tanks are constructedunderground and one recent design incorporates a porous ring at the top of the tank so when it ismore than half full, water seeps back into the ground. The main advantage of designing rainwatercollection systems in this way or in conjunction with seepage wells is that many German cities chargehouseholders an annual rainwater drainage fee, which is waived if rainwater runoff is retained orreturned to the ground allowing significant savings. In Bonn, for example, current annual fees are$1.80 per m2 of roof area and sealed surround, respectively (Knig , 1998).

In many German towns and cities, grants and subsidies are available to encourage householders toconstruct rainwater tanks and seepage wells. In Osnabruck, Wessels, R. 1994: reported that a grant of

$600-$1200 per household was available along with a further subsidy of $3 per m2 of roof areadraining to any tank linked to a seepage well. On the basis of this subsidy, savings in water charges($0.56/m3) and an annual rainwater drainage fees waiver of $1.30 per m2 , the pay back period forinvestment in a tank seepage well system constructed at a new house was estimated to be 12 years.Even without the subsidy and constructing a system at an existing house, the investment would berecouped in 19 years. Costs and the return period on investments would be greatly reduced ifhouseholders were prepared to undertake some of the work themselves.

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BOX 7

Rainwater Survey in Squatter Areas of Tegucigalpa, Honduras.

In a two month survey of Israel Norte and Villa Nueva squatter settlements in Tegucigalpa in 1990

by a local water NGO Agua para el Pueblo the widespread use and importance of makeshifthousehold roof catchment systems was observed (Brand & Bradford 1991). About 85% ofhouseholds were collecting roof runoff and over three-quarters of these were using rainwater for overhalf of their domestic needs. Like many of the barrio settlements on the steep peripheral hillsides highabove Tegucigalpa, Israel Norte and Villa Nueva were not serviced by the main piped water system.Apart from rainwater, residents here depended on the purchase of trucked water from communaltanks, new boreholes, or water vendors and many poorer families typically spent 30-40% of theirincome on sub-standard water.

Over two-thirds of the 535 households surveyed expressed an interest in upgrading their existingstorage tanks usually consisting of a 200 litre oil drum with a 1 000-3 000 litre cement tank. Somealso wanted to improve roofing and guttering or construct new corrugated iron roofs. These familieswere prepared to take on loans of between $18 and $490 to pay for improvements ranging from newgutters to entirely new roof , gutter, and tank systems. In most cases such loans could have beenadministered through an existing scheme and in theory at least repaid over 2 years with savings fromthe water purchases no longer required.

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BOX 8

The Growing Global Interest in Rainwater Harvesting

With development of modern 'conventional' water supply systems in the first half of this century,

many traditional water sources went out of favour. This was the case with rainwater harvestingtechnologies which came to be considered only as an option of last resort. While the exploitation ofrainwater was considered appropriate in certain extreme situations such as on coral islands or atremote farms for which reticulated supplies were uneconomic, little serious consideration was givento the more general use of the technology.

Since around 1980, however, things have changed and there have been numerous grassrootsinitiatives supported by enlightened government and donor agencies promoting and implementingrainwater harvesting technologies. This has partly been a response to the growing technical feasibilityof using roof catchment systems in the South due to the spread of impervious roofing materials inrural areas. It has also been motivated by a paradigm shift regarding global attitudes to theenvironment and the growing realisation that water resource utilization has to become moresustainable.

In 1979 UNEP commissioned a series of regional case studies into Rain and Stormwater Harvestingin Rural Areas. This included work from China, India, Mexico, the U.S., Africa, Australia, and theSouth Pacific. This was the first time a global overview of experiences with the technology werebrought together in a single publication. Another even more influential overview by Pacey, A. &Cullis, A. 1986: followed soon after. At around the same time UNICEF, several bi-lateral donoragencies (including DANIDA and SIDA), and many NGOs were promoting the use of household roofcatchment tanks in East Africa and working on developing various low cost designs in Kenya. Thiswork, much of which was done directly with community groups, led to rapid rates of adoption of rooftanks among rural communities.

In a parallel development, the first conference on the use of rainwater cisterns for domestic watersupply was held in Honolulu, Hawaii in 1982 attracting around 50 mainly academic participants. Itwas not envisaged at the time that the meeting would herald the beginning of a series of internationalconferences on the topic over the next 20 years which would include thousands of participants from avery broad cross-section of countries and professions. The next three conferences took place in theU.S. Virgin Islands (1984), Thailand (1987), and the Philippines (1989) at which point the scope ofthe conference series was broadened to include other forms of rainwater catchment systems such asrainwater harvesting for agriculture. At the 1989 conference in Manila, it was also agreed to set up anAssociation to oversee the conference series and endeavour to promote the technology world-wide.Subsequent conferences took place in Taiwan (1991), Kenya (1993), China (1995), Iran (1997), andBrazil (1999) and the next conference venue in 2001 will be Darmstadt in Germany.

In addition to international conferences, many regional, national, and local meetings and initiativestook place during this period reinforcing the suggestion that the technology is now being given moreattention globally than at any time prior to 1980. These have included: the efforts by the New Delhibased Centre for Science and the Environment to revive traditional rainwater harvesting practices inIndia (Agarwal & Narain 1997); the establishment of a rainwater harvesting forum in Sri Lanka(LRWHF 1999); and new initiatives such as the promotion on rainwater utilization in modernmegacities such as Tokyo (Murase 1994). The Vision 21 initiative has also placed the use ofappropriate technologies such as rainwater harvesting at the centre of its proposed strategies forproviding clean water, adequate sanitation, and hygiene education for 95% of the population by 2025.

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References

Agarwal, A. & Narain S. 1997. Dying Wisdom: The Rise, Fall and Potential of Indias TraditionalWater Harvesting Systems, State of India's Environment 4, A Citizens Report, Centre for Science andthe Environment, New Delhi.

Agarwal, A. & Narain S. 1989. Towards Green Villages, Centre for Science and the Environment,New Dehli, India.

Aminipouri, B & Ghoddousi, J. 1997. Rainwater Catchment for Survival, Proceedings of the 8th

International Rainwater catchment Systems Conference, Tehran: Ministry of Jihad-e- Sazandegi.

Brand, A. & Bradford, B. 1991. Rainwater Harvesting and Water Use in the Barrios of Tegucigalpa,Agua para el Pueblo / UNICEF Honduras.

Cunliffe, D. 1998. Guidance on the Use of Rainwater Tanks, National Environmental Health ForumMonographs, Water Series 3, Public and Environmental Health Service, Dept. of Human Services,

PO Box 6, Rundle Mall SA 5000, Australia.

Gleick, P.(ed.) 1993. Water in Crisis: A guide to the World's Fresh Water Resources, Oxford Univ.Press.

Gould, J. & Nissen-Petersen, E. 1999. Rainwater Catchment Systems for Domestic Supply: Design,Construction and Implementation , London: I.T. Publications.

Knig, K. 1998,Rainwater in Cities, Ecological Concepts, fbr, Kassler Str. 1a, D-60486, Frankfurtam Main, Germany.

LRWHF, (Lanka Rain Water Harvesting Forum) 1999 Rainwater Harvesting for Water Security ,Colombo, Sri Lanka: Lanka Rain Water Harvesting Forum.

Mou, H. et. al. (Editors) 1995. Rainwater Utilization for the World's People, Proceedings of the 7thInternational Rainwater Catchment Systems Conference, Chinese Academy of Sciences, Beijing,China, Volumes. 1 and 2.

Murase, M. 1994. Can Rainwater Utilization Save Cities, Proceedings of the Tokyo InternationalRainwater Utilization Conference, Sumida City, Tokyo, Japan: 33-40. (English and Japanese).

Pacey, A. & Cullis, A. 1986. Rainwater Harvesting : The Collection of Rainfall and Runoff in RuralAreas, London: I.T. Publications

Pearce, F. 1992. The Dammed: Rivers, Dams and the coming world water crisis, London: TheBodley Head.

Postel, S. 1992. The Last Oasis: Facing Water Scarcity, London: Earthscan,.

Thomas, T. 1998. Domestic Water Supply Using Rainwater Harvesting, Building Research andInformation Vol 2, No 2: 94-101.

U.N., 1989. United Nations, Convention of the Rights of the Child, Website:

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U.N.F.P.A 1999. The State of the World Population : 6 Billion: A Time for Choices, United NationsPopulation Fund, New York.

Wessels, R. 1994. Establishment of Rainwater Utilization Plants in Osnabruck, Proceedings of theTokyo International Rainwater Utilization Conference, Sumida City, Tokyo, Japan.

Zhu, Q. and Wu, F. 1995. A Lifeblood Transfusion: Gansu's New Rainwater Catchment Systems,Waterlines, Volume 14.2: 5-7.

Zhu, Q. and Liu, C. 1998 Rainwater Utilization for Sustainable Development of Water Resources inChina., Paper presented at the Stockholm Water International Symposium, Stockholm, Sweden .

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Documents

Contributions Relating to Rainwater Harvesting