:: Specific Design Brief
is a village in north west Sri Lanka, a very dry part of the country. They
have many months when there is no rain. Collecting and storing water
efficiently is vital to them, especially for drinking.
Traditional methods of collecting and using water
For cooking and drinking purposes, they collect
water from the nearest well. In Mahamaddawa, most would have to walk a minimum
distance of between half and one kilometre but for some the distance can be as
great as five kilometres in each direction. This means that the amount of time
spent per day collecting water can vary greatly depending on factors such as;
Traditionally, it was a woman's job to collect water, and it is evident that this tradition continues quite a lot of the time. Women collect water in aluminium containers that can usually hold between four and five litres. Each weighs about four to five kilos. The women traditionally carry them on their hips. Children of both sexes are also likely to help.
Increasingly, the task is being shared more equally. Men can carry more, and travel longer distances in the dry season. They are more likely to have access to bicycles, which also enables them to collect larger quantities.
Research suggests that in the wet season, households make between three and six visits per day to collect water. In the dry season it can be as many as ten visits.
Other problems during dry seasons or drought.
Because of their dependence on subsistence farming, their crops are also hit badly at such times. The only way they can economise is through reducing the amount they eat. Surveys have shown that households reduce their eating from three meals to two per day during the dry seasons, with a consequent impact on their health. Since income is also reduced, they are less able to purchase essentials.
Traditional methods of rainwater harvesting.
Royal palm leaves. People use local clay or bricks to construct a tank, usually with a capacity of about 1,250 litres, enough for 25-30 days' household use (drinking and cooking). They then use a very large palm leaf with a huge surface area to collect and filter the water. It can fill a tank in 3-4 hours of heavy rain. The palm is mounted on four sticks and sloped into the tank to collect rainwater directly. Although it does not bring impurities, the system is vulnerable to strong winds and very heavy rain. One leaf will last for about two weeks during the rainy season. A similar, but less effective system, involves the use of an upturned umbrella.
Tree trunk methods. Coconut and jak trees are preferred. Coconut leaves (which are also large) are tied around the trunks to intercept and harvest water coming down. This system yields about 35-45 litres per day in rains.
Gutters and tanks. People in the area are familiar with the use of guttering and have used their own versions for many years. Gutters are usually temporary and can be made out of hollowed bamboo, galvanised iron sheets, plastic sheets and, recently PVC guttering. They sometimes use some form of downpipe but at others simply allowed water from the gutter to drip into a tank below with the other end of the gutter closed off. Many users practice a system known as "first flush" which means that for the first 30 minutes of rain they don't collect the water, allowing the roof and gutter to be cleaned by the rain. A more permanent filtering system is now in operation in some houses thanks to charitable intervention.
Storing water is then the problem. Many use all available vessels. Others use barrels or cement formed tanks holding up to 300 litres. Once full, they are covered with leaves, polythene sheets or tin. Most last for 5-7 days for an average family.
The design problem. Modern houses with tiled roofs and guttering, can be adapted to rainwater harvesting methods relatively cheaply. ITDG (Intermediate Technology development Group) has joined forces with other non-government organisations, to bring 25 harvesting systems to various houses, as well as 25 for agricultural purposes. These systems can be seen in the accompanying photographs. The tanks cost 20,000 rupees. Most hold either 5,000 or 7,500 litres but they aim to increase the size to hold up to 12,500 litres. During a good year for rain it may be filled between 10 and 15 times but the average is five. People who have them are delighted and have learnt to economise with their use of the water for drinking so that the problem is now nothing like so severe in dry months. One woman told us that the health of her family had improved greatly since the introduction of the system. They now know they have access to clean drinking water as long as they don't overuse it.
However, it is more difficult to devise a system for the coconut thatch roof. An average roof is 50 square metres on one side. The thatch is waterproof so water still runs off well but the house structure lends itself less well to a guttering system, though it would be possible to design one. Particles from the coconut and grass thatching would mean a particularly efficient filtration system would be needed.
Coconut trees are everywhere, and fibre cheaply
available. Bamboo of sufficient diameter is cheap and also locally available.
Clay is available nearby and clay pipes could be made. Cement costs 425 rupees
for a 50 kilo bag. Corrugated iron costs 350 rupees for a 10 ft x 2.5ft sheet.
PVC guttering is available at 100 rupees per metre (3" diameter). Asbestos
sheeting is also widely available. Rocks for tank construction can also be
bought locally at relatively low cost.