|
Report 2 of 5: Heavens Above
- Kenya
Introduction
Two thirds of Kenya is arid or semi-arid and therefore access to water is scarce. Fifty per cent of the population has no access to a safe or adequate supply of water. Women spend several hours each day collecting water from distant dams, sharing the water source with animals that drink from it and contaminate it.
The annual rainfall in Kenya ranges from 150mm to 2,000mm and rainwater is the most common accessible source of water. Rainwater catchment systems have a long history but until recently this simple yet effective method of water collection and supply has been regarded as a last resort. The Kenya Rainwater Association decided to help develop rainwater harvesting technologies in the rural areas.
Uses of domestic water
Levels of domestic water consumption should be 5 litres/person/day although in times of drought or other crises it is not uncommon for the per capita water consumption to fall well below this.
Domestic water demand includes all water used in and around the home for the following essential purposes:
- Drinking
- Food preparation and cooking
- Personal hygiene
- Washing clothes and cleaning
- Washing pots, pans and other utensils
Additional domestic water uses may include:
- Watering gardens
- Watering animals
- Water for construction (repairing mud walls)
In most areas, properly designed household roof catchment systems can normally meet domestic demand for essential purposes.
Rainwater catchment systems
Every rainwater catchment system consists of three main components:
- a catchment surface where the rainwater runoff is collected
- a storage reservoir where the rainwater is stored until required
- a delivery system for transporting the water from the catchment system to the storage reservoir, e.g. gutters and drains.
The actual amount of rainwater that can be supplied depends upon the amount and distribution of rainfall, the size of existing or affordable catchment surfaces and the volume of the storage tank.
Roofs provide the most common and least expensive way of harvesting rainfall. Corrugated iron, plastic or tiles are all good surfaces for rainwater catchment but tightly thatched roofs made from coconut palms may be equally suitable.
© John Gould and Erik Nissen-Petersen /
Rainwater Catchment Systems for Domestic Supply
|
Storage tank design
For most rainwater harvesting systems, the storage tank represents the single greatest cost. This is especially true for roof catchment systems where an existing roof structure provides, in effect, a free catchment area.
There are many ways to construct a household rainwater tank. The key features of any tank are that it should be watertight, durable, affordable and not contaminate the water in any way. The most appropriate choice of tank will depend on local conditions and the availability of local materials as this will directly affect the cost.
There are a number of key requirements common to all effective tank designs:
- a functional and water-tight design
- a solid, secure cover to keep out insects, dirt and sunshine
- A screened inlet filter
- A screened overflow pipe
- A manhole (and ideally a ladder) to allow access for cleaning
- An extraction system that does not contaminate the water, e.g. tap/pump
- A soakaway to prevent spilt water forming puddles near the tank
- A maximum height of 2 metres to prevent high water pressures (unless additional reinforcement is used in the walls and foundations
Construction of the water storage tank
The site needs to be free of anthills, latrines, waste pits and tree stumps to ensure that a solid foundation can be built for the tank. Once a suitable site has been found, a circle is drawn on the ground with a radius 15cm longer than the external radius of the tank. The foundation must be sealed with concrete within 24 hours or there is a danger of leaks and cracks. The tank walls should be round as these are stronger than rectangular walls. Bricks, blocks, concrete or ferrocement can all be used to build the tank walls. It is essential to cover the tank with a roof to prevent evaporation and stop the water becoming dirty.
The delivery systems used for roof catchment systems usually consist of gutters suspended from the eaves sloping towards a downpipe and tank. The gutters must be fitted properly to ensure that they operate at optimum capacity. They should be angled with a gentle slope leading into the tank.
Group cooperation
As a result of the work carried out by the Kenya Rainwater Association, rainwater catchment systems have been adopted by women’s groups in the Laikipia district in Kenya. Money is collected by the women and as soon as they can afford to buy the materials to build a water tank, they pick a member by drawing lots and start to build a rainwater tank in her compound. They hire a skilled worker to guide them but carry out most of the building work themselves.
The women, who used to walk about 10 km with water on their backs, no longer have to spend hours collecting water and can spend more time on growing vegetables or poultry farming, thereby improving the family diet. Some women have even started to plant trees and sell seedlings to generate extra income and they can now afford to send their children to school.
For further information, please contact:
Intermediate Technology Development Group would like to acknowledge John Gould and Erik Nissen-Petersen, the authors of Rainwater Catchment Systems for Domestic Supply, and the Kenyan Rainwater Harvesting Association, in particular John Mbugua, for providing the original material on rainwater harvesting systems. ITDG would also like to thank SIDA (Swedish International Development Agency) for providing financial assistance for the rainwater harvesting project.
N.B. Rain falls in moderate quantities almost everywhere that people live and, except in hostile arid desert and polar environments, rainwater collection is usually viable to some degree.
The Kenya Rainwater Association and FAKT have produced a half hour video promoting rainwater harvesting for sustainable development. The video is called "Mvua ni Maji" – Rain is Water – and is available in French, German and Swahili from FAKT.
This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
|
