Rain Water Harvesting Technologies in Sri Lanka

SARID, January 2004

By Vinod Moonesinghe

(Writer is the editor of the Environment Foundation Ltd., Sri Lanka & a SARID project coordinator)

Water is a resource under considerable pressure from population growth and global warming, so alternative, low-cost sources take on an added importance. Among these sources rainwater harvesting stands out, especially in Third World countries with high rainfall.

In Sri Lanka, notwithstanding the saying of King Parakramabahu the Great that not a drop of water should flow unused to the sea, the uninterrupted supply of water for domestic purposes has long been taken for granted. The water-supply infrastructure has not kept pace with needs and rainwater harvesting has not been promoted as in India, where urban authorities have amended their by-laws to facilitate it.

In 1995, the World Bank assisted Community Water Supply and Sanitation Project (CWSSP) conducted a study of the feasibility of rainwater harvesting for domestic use, incorporating rainwater harvesting into official water supply schemes in Sri Lanka. This led to the development of some low-cost technologies that helped the spread of rainwater harvesting, which had been retarded somewhat due to the high cost of storage and other facilities (1). Of note was the ‘Pumpkin Tank’, a low-cost (given as SL Rs 5,000 or Sterling £ 77) pumpkin-shaped ferrocement tank for use above ground level (2), (Fig.1) and a 5m3 underground brick built tank, based loosely on the design of the Chinese below ground biogas tank - the Sri Lankan engineer who designed the system had studied for some years in China, an example of cross fertilisation of appropriate technologies (3), (Fig. 2)

Fig. 1: Pumpkin Tank

Fig. 2: Underground Tank

.So far, there are just 14,000 rain water harvesting systems functioning in the country. Of this total, Badulla, Hambantota and Matara districts have 39%, 25% and 8% respectively, while the next six, Moneragala, Putlam, Kegalle, A’pura, Kalutara, Kurunegala have 22% between them. The remaining 15 districts (including the urban agglomeration around Colombo) account for only a tiny proportion. So there is obviously a lot of scope for the expansion of rain water harvesting (4).

Lanka Rain Water Harvesting Forum

In March 1996, a small group of people, from a range of institutions which had been involved in rain water harvesting, established the Lanka Rain Water Harvesting Forum (LRWHF) as a single institution for propagating it in this country. Among its objectives are the identification of existing rain water harvesting practices in Sri Lanka, the further development of techniques for collection and the initiation of further study to make recommendations for maintaining good practices.

The LRWHF carries out research and development into low cost storage techniques and the suitability for rainwater harvesting of different roofing materials. While monitoring the durability of present practices, it surveys the water user pattern and water security and tests the quality of collected water. It has established an information network on a district basis - linking it with the users, agencies, NGO’s and individuals - and a pool of skilled masons who are trained in planning, design and constructions of rainwater harvesting systems (5).

Starting in August 1998, the LRWHF participated in a three-year research programme, funded by the European Commission, called the Domestic Roofwater Harvesting in the Humid Tropics project, carried out by an international consortium known as the Roofwater Harvesting Research Group. The aim of the project was ‘to generate reliable information about domestic roofwater harvesting for water policy planners, supply professionals and, ultimately, householders’ (6).

Several technologies were identified by this research. One was a 3-cubic-metre (106 cu ft) tank for use at ground level: a rectangular 1.5 x 1.5 x 1.5m (5’ x 5’ x 5’) brick structure with a concrete base, cement rendered inside and out, costing about SL Rs 5,000 (stg £75.00). The cover is a fine nylon mesh which acts as a filter for debris. A PVC downpipe delivers water - collected on roof by conventional factory-made poly-vinyl-chloride (PVC) guttering - into the tank through the cover. Water is extracted through a small removable section in the nylon mesh, using a small bucket. The tank has an overflow and washout and is easy to clean because the walls are at chest height (7).


The LRWHF also tries to promote the application of rain water for domestic purposes through information, communication and awareness-raising.
In June 2003, the LRWHF advertised a competition to design rain water harvesting systems and components for urban households. There were two main categories, Medium Income housing and Low Income housing, plus a sub-category for components (water filters, devices for flushing out the first fall of rain). The designs were either to be incorporated into new house designs or else to be added onto existing houses.

Of the prize winning designs, several stand out (8). The first prize in the Middle Income category was won by A.N. Abeywickrama of Matara. His design had some unique features. The feed from roof was through a mesh filter into a cylindrical tank (brick with 8 pie-slice-shaped covers). The outlet was fed through a PVC pipe with holes in it and a sand filter and pumped into the main storage tank. An ingenious ball-float device for removing first rain completed the system.

Danushka Bandara, a school student from Anuradhapura, won the second prize with an original design, with the tank as part of the roof itself and requiring no pumping. The tank was covered by a 1/16” (1.6 mm) corrosion-resistant mesh. At the mid-level of the tank lay a charcoal / rubble / sand / cotton layered filter, sandwiched between another 1/16” (1.6 mm) corrosion-resistant mesh (on top) and a 1/32” (0.8mm) corrosion-resistant mesh below.

There were two joint second prizes instead of a first prize in the Low Income category:

GJ Bandara of Polonnaruwa. Based on a large black plastic tank, with a cylindrical aluminium inlet filter (filled with rubble) lowered into the access hole at the top. A plastic or tin bucket or can, filled with rubble, was hung on the outlet tap, to serve as a filter.

KPSP Perera of Kotte. The main innovation was a storage tank based on a thick tube of 3 ft (0.9 m) wide polythene (used for packaging and concrete work), slit along one edge and sunk into a 2 ft (0.6 m) deep, 2ft (0.6 m) wide trench. The upper cover of the tank was another thick polythene. Extraction was by hand-pump. The system had been operational for three months at the time the design was submitted (Figs. 3 and 4).

Polythene Tank

Fig. 3: Uncovered

Fig. 4: Covered

The Third Prize was won by RAAR Ranasinghe from Veyangoda whose system was based on 500 litre volume Ferro cement tank. It had a U-trap built into the inlet from the gutter to trap dirt and remove it, via a pipe, to the first-flush device. The inlet filter was an 18” (450 mm) tall cylinder with a 4” (100 mm) layer of sand and a 6” (150 mm) layer of rubble and coconut charcoal. The outlet filter was a PVC strainer on the outlet pipe, raised inside the tank to prevent ingress of sediment, leading to a bib-tap and washout valve.

The prize for components was won by Dulip Gunawardena of the National Water Supply & Drainage Board, the components being an outlet filter and a depth gauge. The former consisted of a floating device (shaped like a lotus) with a flexible hose attached. The floating device had v-shaped notches through which the surface water could flow, any floating debris being trapped between the teeth. The depth-gauge consisted of a floater made of 3 PET bottles fixed together, with a plastic pipe extending upwards with depth markings on it.
Although the number of entries was relatively low, the respose to this competition show that there is considerable talent innovative talent in Sri Lanka which could be utilised in further developing low-cost domestic rain water harvesting. What is required is a greater effort to further this technology. The state should provide incentives (not necessarily monetary – as for instance the Indian Municipal by-law amendments) in order to properly harness this potential in a meaningful manner.


1. Tanuja Ariyananda, Rainwater harvesting as a water supply option in rural Sri Lanka, East Asia 2000 Regional Rainwater Utilisation Symposium, International Rainwater Catchment Systems Association.

2. University of Warwick Development Technology Unit, Domestic Roofwater Harvesting Research Programme, Case Study 1: the Sri Lanka Pumpkin Tank. http://www.eng.warwick.ac.uk/DTU/pubs/rn/rwh/cs01/cs1.html

3. University of Warwick Development Technology Unit, Domestic Roofwater Harvesting Research Programme, Case Study 2: Underground brick dome tank, Sri Lanka.

4. Lanka Rain Water Harvesting Forum, Distribution of Household RWH Systems in Sri Lanka.

5. Lanka Rainwater Harvesting Forum.

6. University of Warwick, Development Technology Unit, Domestic Roofwater Harvesting Research Programme, Case Study 3: 3.0m3brick built storage tank, Sri Lanka.

8. Information supplied by Tanuja Ariyarnanda of LRWHF.

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