Gift from the Sky – Sri Lanka


November 2004

Rural communities in Sri Lanka often struggle to gain access to clean water without having to travel miles everyday. While many options exist to get clean water to rural communities, these options are often expensive and locally inappropriate. However, rainwater harvesting may be the optimum solution. By making use of the plentiful rain of the wet season, and filtering it through a roof-based collection system, rural communities can have a year-round supply of water suitable for cleaning and, if boiled, for drinking.

Sri Lanka’s Water Supply

Sri Lanka is endowed with approximately 4500 km of rivers, 2400 km of irrigation canals and 3500 deep-water tanks, reservoirs, and artificial and natural wetlands. 48 million people (26 per cent of the population) are provided with piped water and 1.4 million (8 per cent) are provided with tube-well water. In addition, 27 per cent of the rural population obtains safe drinking water from dug wells. Accordingly, 90 per cent of the urban population and 57 per cent of the rural population are provided with safe drinking water facilities.

© Zul/ITDG
© Zul/ITDG

However, the Comprehensive Assessment of the Freshwater Resources of the World (1997) predicts that two-thirds of the world’s population will experience water stress conditions by 2025. According to UN studies, countries that withdraw their available water resources at a rate of 40 per cent or more will experience high water stress conditions, thus prompting urgent management of water supply and demand. In south Asia withdrawal of available water resources occurs at a rate of 48 per cent. Sri Lanka is therefore likely to experience an acute shortage of water if stringent measures are not adopted to manage demand and supply of water.

The overall situation is that the provision of good quality drinking water is becoming a challenging task: water sources dry up, the remaining water becomes polluted, and there is growing demand due to population pressure leading to increased conflict among users. Although Sri Lanka receives a mean annual rainfall of 1200 mm, high variability and non-uniform distribution creates periodic shortages of water for both irrigation and domestic use. The dry zone of Sri Lanka, which covers two-thirds of the country, largely depends on irrigation for cultivation, sanitation and drinking water. While irrigation has played a significant role in the history of Sri Lanka, domestic water supply has had its own mode of development. For domestic use, the rural peasantry in Sri Lanka mostly use groundwater from dug wells.

In the sparsely populated dry zone, people also use irrigation reservoirs and canal water for domestic use, especially in the dry season when groundwater sources are depleted due to increased demand and high rates of evaporation. Often the reservoir waters are not fit for human consumption due to contamination in extremely dry conditions. Cattle and humans frequently meet their water needs from the same source. This situation prevails in most parts of the North Central, North Western and the drier parts of the Southern Province. In these areas, the mean annual rainfall is 1000-1750 mm and evaporation is high in temperatures beyond 27°C in the dry season.

© Zul/ITDG
© Zul/ITDG

As a result, rural people in Sri Lanka may walk up to 10 km to acquire water in the dry season. In some parts of the wet zone, where water is not available to households due to the low groundwater table, people often have to negotiate steep terrain to fetch a limited quantity of water. These practices have become a daily routine in the life and times of rural people. In most cases it is the women who take on the role of collecting water, thus sacrificing time that could be spent with their families and on other household chores.

 

‘I had to go about 2 miles to get good water. I had kidney trouble because we took water from a local pump and then when I went to another well I found I still had the same problem.’
(Ismil Sithli Mauruffa, village dweller)

At present 60 per cent of the rural population has access to safe drinking water. This leaves a significant population in rural Sri Lanka where none of the conventional water supply sources can provide water due to financial, technical or management reasons. Rainwater harvesting (i.e. collection and storage), as promoted by the Lanka Rainwater Harvesting Forum, has proved to be one of the most viable options for these communities, provided they are prepared to contribute as equal partners in the implementation process.

Lanka Rainwater Harvesting Forum

The forum was established at the beginning of 1996 by a small group of people interested in establishing rainwater harvesting as a viable means of water collection in Sri Lanka. Members of the forum come from a range of governmental and non-governmental backgrounds, including the National Water Supply and Drainage Board (NWSDB), Intermediate Technology Development Group Sri Lanka (ITSL), Community Water Supply and Sanitation Project (CWSSP), Church of Ceylon Board of Women’s Work, NGO Water Supply and Sanitation Decade Services, Agrarian Research and Training Institute (ARTI) and the Open University.

The aims of the forum are to:

  • Identify existing rainwater harvesting practices in the country;
  • Develop further techniques for collection of rainwater;
  • Promote the application of rainwater for domestic purposes through information, communication, and raising awareness;
  • Initiate further studies to make recommendations for maintaining good rainwater harvesting practices.

Rainwater Harvesting

Examples of rainwater harvesting (RWH) systems can be found in all the great civilisations throughout history. In industrialised countries, RWH systems have been developed with the aim of reducing water bills or to meet the needs of remote communities or individual households in arid regions. Traditionally, in Sri Lanka, rainwater is collected from trees, using banana leaves or stems as temporary gutters; up to 200 litres may be collected from a large tree in a single storm. Many individuals and groups have taken the initiative and developed a wide variety of RWH systems.

© Zul/ITDG
© Zul/ITDG

The people of Sri Lanka devised their own system of collecting rain when the need arose. However, most of the traditional rainwater harvesting was limited to small quantities collected into household utensils. While different types of traditional rainwater harvesting were in use, roof-water harvesting appears to be the most effective in terms of quantity and adequacy. For quality and drinking purposes, people mostly used tree-trunk rainwater harvesting or open-air rainwater harvesting methods. Those who practised roof-water harvesting consisted mainly of those with permanent roofs made from tiles or tin sheets. In very remote villages, and in most trying conditions, people have even used thatched roofs to harvest roof runoff, although they were not using it for drinking.

Rainwater Harvesting in Dematawelihinna Village, Badulla District

Many options for providing water to the village were considered at the initial stages of a Community Water Supply and Sanitation Project (CWSSP). A natural spring was identified which could provide water to 45 households; this was rejected, as there were 204 families in the village. The second option was dug wells. This too was discarded due to the difficulty of raising water and the high cost of construction. The third option of tube-wells was investigated and 15 locations were identified. The cost of the tube- well project was estimated at Rs.871,611 (US$19,400) from state support and Rs.51,547 (US$1,145) from community funds. However, this option was rejected on technical grounds. Another option was pumping water from the town water supply tank. The estimated cost of this option was Rs.3 million (US$66,644). The total funds allocated to supply water to Dematawelhinna Village were only Rs.1.1 million (US$24,436), meaning that the difference would have to be borne by the village community. Each household would have to contribute Rs.2000 (US$44.42) to the cost of the option and a monthly contribution of Rs.145 (US$3.22) for operation and maintenance of the pump houses. Therefore, although technically feasible, the option had to be rejected due to cost considerations.

Thus, with all the centralised options failing, rainwater harvesting from roof catchments was decided to be the only viable option available. The total estimated cost of the entire project was Rs.1,314,706 (US$29,205) with a total community contribution of Rs.262,025 (US$5,820 – 20 per cent of project cost) which included labour and material. Initially, the majority of villagers had rejected the rainwater option due to health reasons. Villagers questioned the possibility of mosquito breeding in the stagnant waters, and of the first 100 suggested rainwater tanks only 46 households consented. However, at the first meeting, when all other options were ruled out, a further 100 households consented. At present there are 146 rainwater tanks constructed in the village.

Rainwater Harvesting Technology

Storage tanks

© Zul/ITDG
© Zul/ITDG

The water storage tank usually represents the largest capital investment element of a domestic RWH system. It therefore requires careful design to provide optimal storage capacity, while keeping the cost as low as possible. Vessels that are commonly used for very small-scale water storage in developing countries include plastic bowls and buckets, jerrycans, clay or ceramic jars, cement jars, old oil drums and empty food containers. For storing larger quantities of water the system will usually require a tank (above ground) or a cistern (below ground). These can vary in size from a cubic metre (m3 or 1000 litres) to hundreds of m3 for large projects. For a domestic system, they are typically up to a maximum of 30 m3. The choice of system will depend on a number of technical and economic considerations, including:

  • Space availability;
  • Options, materials and skills available locally;
  • Local traditions for water storage;
  • Cost – of purchasing new tank;
  • Cost – of materials and labour for construction;
  • Ground conditions;
  • Style of RWH – whether the system will provide total or partial water supply.

Arguments for and against using a tank or cistern for water storage

Tank Cistern
Pros
  • Above-ground structure allows easy inspection for leakages
  • Many existing designs
  • Can be easily purchased
  • Can be manufactured from a wide variety of materials
  • Easy to construct from traditional materials
  • Water extraction can be by gravity in many cases
  • Can be raised ground level to increase water pressure
  • Generally cheaper due to lower material requirements
  • Less risk of accidentally emptying by leaving the tap on
  • Require little few workings above ground
  • Unobtrusive
  • Surrounding ground gives support, allowing thinner walls and lowering costs.
Cons
  • Requires space
  • Generally more expensive
  • More easily damaged
  • Prone to attack from weather
  • Failure can be dangerous
  • Water extraction is more problematic, often requiring a pump
  • Leaks are more difficult to detect
  • Contamination of the cistern from groundwater is more common
  • Can be damaged by vehicles and tree roots
  • There is danger to children and small animals if the cistern is left uncovered
  • Flotation of the cistern may occur if groundwater level is high and cistern is empty.

Collection surfaces

For domestic rainwater harvesting the most common surface for collection is the roof of the dwelling. The style, construction and material of the roof all affect its suitability as a collection surface for water. Typical materials for roofing include corrugated iron sheeting, asbestos sheeting, tiles of a wide variety, slate, and thatch (from a variety of organic materials). Most are suitable for water collection, but only certain types of grasses, such as tightly thatched coconut and anahaw palm, can provide a surface adequate for high quality water collection. The rapid move towards the use of corrugated iron sheets in many developing countries favours the promotion of RWH (despite the other negative attributes of this material).

Guttering

© Zul/ITDG
© Zul/ITDG

Guttering is used to transport rainwater from the roof to the storage vessel. Guttering comes in a wide variety of shapes and forms, ranging from the factory-made PVC types to home-made guttering using bamboo or folded metal sheet. The lack of standards in guttering shape and size makes it difficult for designers to develop standard solutions. Guttering is usually fixed to the building just below the roof and catches the water as it falls from the roof.

 

 

green-current-giftfromthesky6

Factory-made gutters are usually expensive and therefore beyond the reach of many communities in water-deprived areas. They are seldom used for very low-cost systems. The alternative is usually to manufacture gutters from materials that can be found cheaply in the locality. A number of techniques have been developed to help meet this demand, which are covered in ITDG’s technical briefs on rainwater harvesting.

Filtering and Settling Tanks

Systems are available for treating water before, during or after storage. The simple ‘trash rack’ has been used in some systems, but this type of filter has a number of associated problems: it only removes large debris, and the rack can become clogged easily and so requires regular cleaning. The sand–charcoal–stone filter is often used for filtering rainwater entering a tank. This type of filter is only suitable, however, where the inflow is slow to moderate, and will soon overflow if the inflow exceeds the rate at which the water can percolate through the sand. Settling tanks and partitions can be used to remove silt and other suspended solids from the water. These are usually effective where used, but add significant additional cost if elaborate techniques are used. Many systems found in the field rely simply on a piece of cloth or fine mosquito mesh to act as the filter (and to prevent mosquitoes entering the tank).

The Impact of Rainwater Use in Dematawelihinna

The 5m3rainwater tanks used in the project were designed to supply 20 litres per person for a family of five for a 50-day dry period. However, water stored in these tanks is being used throughout the year due to intermittent rain received in the wet season. During the dry season, which usually lasts for four or five months, the water-use pattern changes as families fetch more spring water and try to maintain the rainwater storage as a security. During the wet season, rainwater tanks are used to store water for bathing and washing clothes. However, some of the villagers located at the far end of the Dematawelihinna peak use only rainwater for all domestic needs. The reason for total dependence on rainwater is the physical location of the houses which are further away from natural springs or dug wells than the other houses.

The most significant impact of rainwater harvesting in the community is the assured supply of domestic water to the home. This has led to the increased use of water to improve personal hygiene. There has also been an impact on social life. Previously, people in water-scarce areas had to restrict their social life due to the pre-occupation with fetching the daily quota of water. The mere presence of assured water has changed their life style dramatically. With the availability of a 5m3tank, the users could entertain friend and relations, indulge in social visits and attend career development programmes without having to think about the problem of domestic water requirement. In Dematawelihinna, school teachers had previously complained of poor school attendance and frequent failure to complete homework, attributed to the children fetching water in the night. This problem has been totally eliminated since the introduction of rainwater tanks.

Though water-borne disease is a common occurrence among users of polluted water, this has not been reported as a serious problem in Dematawelihinna since the rainwater tanks were constructed. A common perception is that rainwater is unfit to drink, especially when it is collected from roof catchments. However, tests conducted on quality of rainwater indicate that it is fit to drink after boiling, and the lack of water-related diseases reported by the villagers after using the tanks supports this.

Further Information

Participating Organisations

Lanka Rainwater Harvesting Forum www.rainwaterharvesting.com

National Water Supply and Drainage board (NWSDB) waterboard.lk

Donor and Supporting Organisations

Department for International Development (DFID) www.dfid.gov.uk

USAID www.usaid.gov

World Bank www.worldbank.org

Resources

ITDG Technical Briefs answers.practicalaction.org

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