Rainwater harvesting in Sri Lanka
Nearby three quarters of Sri Lanka lies in what is widely known as the 'Dry Zone', comprising the northern half and the whole of the east of the country. Average annual rainfall in this region is generally between 1,200-1,800 mm. Annual 2540 mm to over 5080 mm in south west of the Island and less than 1250 mm in the northwest and south east of the Inland . Due to availability of alternative water sources in the past, there is no longer tradition of rainwater harvesting for domestic supply. Nevertheless, in many hilly areas lacking access to reliable wells or gravity fed piped supplies water collection often involves a long trek to distant sources with a long uphill walk carrying a fall container.
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 hundred 5-millimeter cubic tanks for household water supply. Two designs were developed a sub surface brick tank and a surface forrocement tank. For an average sized roof of 60meter cubic a household in the project area could expect a rainwater supply equivalent to between 150-200 liters/day or even higher during wetter part of the year. The lankan rainwater-harvesting forum was established in 1996 to promote the application of rainwater for the application of rainwater for domestic purposes throughout the country and to develop technology and establish guidelines for good rainwater harvesting practice.
With adequate rainfall allover the country, harvesting was a feasible option to provide safe drinking water to many communities living in hill settlements in the central hill country and to those living in north central and southern dry zones. In the latter two areas, communities either had no access to safe drinking water or the available groundwater was too brackish to drink. In southern dry zone, salinity of groundwater was a major threat to human consumption, due to this people traveled for long hours to nearby town supply source or community well. Due to difficulties of collecting safe drinking water, people in the dry zone have their own traditional rainwater harvesting systems. The system was used during rain season and their collection were limited to household utensils as there was no storage.
The technology adopted the traditional wisdom of harvesting roof runoff, merged tanks with new technology, and five cubic meter cement mortar tanks were constructed at the household level to harvest and store rainwater. The first experiment of organized rainwater harvesting began in a village called dematawelihinna in bedulla in the central hills of Sri Lanka These tanks were of two types: surface tanks made of forrocement and underground tanks made of brick mortar. The total cost of these tanks varied from Sri Lankan rupees 7,000-9,000 (us$90-115) depending on the type of tank. At present there are about 6,500 tanks constructed in five districts of Sri Lanka. Initially CWSSP implemented the rainwater harvesting system and further it was taken by some non-government organizations as a means of water supply too poorhouse holds in rural Sri Lanka. The beneficiary contribution in construction has increased from 20% to 50% and given better sense of ownership.
Rooftop water harvesting is practiced using a variety of materials such as tin sheets, bamboo gutters, banana stem files, arecanut (areca catechu).
1.Tin sheets: this is a techniques where people use sheets formed into the shape of a gutter, tied with jute or coir ropes and attached to the full length of the roof. At the end of the gutter, royal palm leaves or barks of trees are used to form a funnel shape to avoid splashing of water at the point of exist. These tanks usually hold 225-350 liters of water. Cadjan leaves close this storage. However, as the system of storing is not very secure water cannot be used for 5-7 days depending on the family size. The water, thus, collected is mainly used for drinking, which is boiled or filtered before consumption.
2.Banana stems files: mostly the poorer community uses this technique. Banana stem are tied to a corner of the roof firmly. At times of heavy rains, props to prevent falling under heavy water pressure support the banana stem files. The problem with system is that banana stem files have to be replaced frequently as they tend to break with 3-4 days of heavy rains. Users of this technique collect 6-7 pots of water under average rain conditions. This technique may appear primitive but it is very useful to poor who do not have the capacity to buy polythene sheets or galvanized sheets.
3.Arecanut (areca cetchu): this technique uses arecanut sheaths as a temporary gutter to collect rooftop runoff. The quantity of water that can be collected using this system is limited and the sheath needs to be replaced at least once every two weeks.
Open rainwater harvesting: in open rainwater harvesting, a number of materials are used to capture the rainfall directly from the skies.
1.Royal palms (borassus flabllifier): in this technique a large royal palm tree leaf is placed on a wooden stand in open air. The rainwater is collected directly and is thus cleaner than roof runoff water. This method appears to have been extensively used in the past. Under good rainfall conditions a large royal palm leaf can collect as much as 200 liters of water per day.
2.Poythene sheets: this technique is used with a polythene sheet 3 meters (m) * 3m in size, spread across in the open air devoid of trees, to collect direct rainfall. The water thus collected is cleaner than run off water. While this technique collects clean drinking water. It is expensive to buy polythene sheets and the polythene is vulnerable to damage under heavy wind conditions.
3.Galvanized sheet: this technique uses a 2m x 1m galvanized sheet in the open air to collect direct rainfall. The galvanized sheet is tied from the two corners in the shape of a boat. The sheet is mounted on four or six poles in the open air. Only limited quantity of water is collected. While this system collects clean water for drinking, the drawback is that it is costly to
purchase galvanize sheets and the sheet can rust if not maintained properly.
4.Tree trunks: this is evidence that in the past, people constructed boat-like structure from large tree trunks and lifted it in the open air to collect direct rainfall. These structures were about 2.6 m in length with a similar depth cavity constructed to collect rainwater.
5.Natural rock cavities: in one temple in monaragala there is evidence to suggest that rainwater was collected in large (4m*1m) rock cavities constructed in large rock surfaces.
Buddhist priest used this water to wash their robes. Presently, people in the neighborhood use this water for drinking during the rainy season.
Rainwater harvesting with inverted umbrella
Rainwater is harvested by using an inverted umbrella in galvanized bucket. This technique is used in combination with other rainwater harvesting techniques, since only limited quantity of water can be collected is used for drinking purposes.
Rainwater harvesting experiences in Anuradhapura district indicate that householders collect rainwater not because of the lack of drinking water but because of the better quality of rainwater. Capacity to collect and store sufficient rainwater is limited due to poor economic status of these households.