According to the Public Investment Programme of 1996-2000 Sri Lanka needs to invest Rs 8000 million (US$ 112 million) annually to achieve safe drinking water for all by year 2010 (Ariyabandu, Ariyananda & Hapugoda, 2000). The current annual expenditure amounts only Rs 3500 million, inadequate to meet the demand for water, due to rising investment costs, increasing operation and maintenance cost, conflicts among the water users, drying of water sources, and population growth. The heavy public investment on water supply schemes enable to supply piped born water only 32% of the total population.

Table I: Current Water Supply Situation

Description Urban Rural Total

% served by piped water 75 14 32

% served tube wells 10 11 11

% served by protected dug wells 10 40 24

% served by other means 05 35 33

Therefore, hunting for alternative sources of water become vital from household level to macro level policy planning and domestic rainwater harvesting is one such option to overcome the water crisis.

Rainwater as a stand-by resource, a complement to the existing main supply or for the entire use for domestic and agricultural purposes is nothing new. The early Roman practices of roof catchment systems when Roman villas and even whole cities were designed to take advantage of rainwater for domestic use. In Asia and Africa rainwater harvesting has a very long history and collecting rainwater in traditional jars or via gutters have been practised in countries like Thailand and certain parts of Africa. In Sri Lanka rainwater harvesting technique has been used even in the 5 century rock fortress of Sigiriya, with its network of storage, reservoirs, swimming pools, mirror pools, artificial streams and fountains. However, with the introduction of pipe born water supply in the last century, many rainwater-harvesting techniques have been forgotten.

Several developments around the world in the past five years confirm the proposition that both interest in and development of rainwater catchment systems technology is continuing to grow (Gould John, 2000). In China, the rapid expansion of rainwater harvesting on the Ioess plateau for both domestic water supply and agriculture which has already benefited over 1.2 million people in Gansu, province alone. In Iran there are now many systems of bunds in the arid interior for diverting runoff water from the mountainous areas to recharge aquifers in the surrounding plains or supply villages. Also, the use of micro catchments on eroded hillsides to encourage re- vegetation and reafforestation has also become important and common. In rural Australia harvesting of rainwater is widespread and over a million people depend on it for either part or all of their domestic water needs. Many institutional rainwater tanks have been installed in Africa in the last decade, reviving a tradition from earlier in this century. In Europe and Japan where rainwater had fallen out of use, there has been a considerable revival in the last decade driven by environmental concerns. (Thomas Terry, 2000).

The mean annual rainfall of Sri Lanka is around 2,000 mm, ranging from 900 mm to 5500 mm in different regions. It is a common misconception that tropical countries with high average rainfall do not need to harvest rainwater for domestic use. Sri Lanka is one such country which, until recently, had the notion that rainwater harvesting (RWH) was not a viable option for supplementing rural water supply (Ariyabandu, Ariyananda & Hapugoda, 2000). The benefits of a better water supply begin with convenience of having water in the premises, saved time, less effort and enable the women to make choices, since women are the primary care-givers in Sri Lankan households, traditionally they are responsible for assuring supply of water for domestic purposes.

Lanka Rainwater Harvesting Forum (LRWHF) is actively involved in promoting the simple technique of domestic rainwater collection, especially in rural areas and the effort is much meaningful for further expansion. Rainwater harvesting techniques successfully practiced in rural areas offer much hope supplementing the conventional sources of water supply. Studies in rural areas have shown that rainwater harvesting beneficiaries use more water per capita than the non beneficiaries, specially for washing and toilet purposes (Ariyabandu, R. de S., 1999, WEDC, Ethiopia). Collection of rainwater improves the water security and thereby has had an indirect impact on food security and health security.

Rainwater harvesting is the collection, concentration and storage of water that runs of the natural or man made catchment surface (Rajkumar, 2000). At household level, the catchment area is often the rooftops made of asbestos, GI sheets or tiles, directed through a gutter to storage tank. The volume harvested depends on the amount of rainfall, the area of the catchment (roof) and the run- off coefficient. The storage tanks can vary in size and form. The most commonly used are brick built tanks, and ferocement tanks and can be built underground of aboveground A good quality water can be obtained from a roof harvesting system provided the following are considered (Rajkumar, 2000).

* Roof material to be non toxic

* Roof surface to be hard enough to be cleaned, less likely to be damaged and shed material into the water

* No painting is needed since most paints contain toxic substances

* No trees having branches overhanging the roof

* Nesting of birds on roof is prevented

* Installation of a first flush device

* The storage must have a roof that fits tightly and prevents entry of light, with a manhole cover, and flushing pipe at the base of tank

* To avoid contamination of water, a hand pump or a gravity tap being installed

The quality of the collected rainwater from the pilot project sites in Kandy and Puttalam was laboratory tested and compared with other water sources in the surrounding areas and the results are as follows.

• The PH was high in the new rainwater tanks due to cement dissolving. This improved after the tanks were washed and flushed several times.

• WHO standards on the conductivity of drinking water were maintained in all the rainwater harvesting tanks

• WHO standards on the total hardness of drinking water were maintained for all rainwater tanks

• All rainwater harvesting tanks passed the WHO requirement on turbidity for drinking water

• E-coli counts per 100 ml of water indicates the fecal contamination of water. Of the 6 rainwater harvesting tanks sampled, 3 failed the WHO standards for E-coli.

Due to stagnant water in gutters and tanks, mosquito breeding is quite common in this system. Keeping the gutters clean and storage closed can prevent the above problem. Experience in Ahaspokuna in Kandy has shown that mosquito breeding could be prevented by raring fish in these tanks (Rajkumar, 2000). Or else, if the tank is tightly sealed, it serves both in preventing the breeding of mosquito larvae and the growth of algae and thereby improves the quality of the harvested rainwater.

Urban areas’ micro catchments point towards the roof, and paved areas whose yields so far been generally not taken into consideration. Therefore, designing a programme for the collection, treatment, storage and supply of rainwater may yield a better solution to the urban population, since the finance and the availability of water resources become major limiting factor. Promoting rainwater harvesting in urban and urban slums need more awareness, education and a few demonstration tanks. LRWHF hopes to undertake a pilot project on rainwater harvesting technology for urban households. By implementing the knowledge gained to improve rainwater harvesting technology in Sri Lanka can provide additional water source for domestic and non domestic purposes for urban communities, reduce the cost and use of chemicals for treating water, reduce flooding problems in urban cities and enhance the ground water table by limiting the number of users on ground water.

Therefore, domestic rainwater harvesting has to be given serious consideration while designing new houses, housing schemes and even the commercial buildings in order to collect the rainwater. Engineers, architects, policy makers and even individuals and the community has to play important roles on this regard to minimize the water scarcity problem which will create tremendous pressure not only to the nation but also to the globe.
Courtesy: Lanka Rainwater Harvesting Forum