by Dai Rees.
The Development Technology Unit of Warwick University aims to research and promote technologies appropriate for practical use in the Third World. The Unit has recently developed three small jars (between 500 and 750 litres) for rainwater storage. Their aim was to develop a number of safe, low-cost alternatives for rainwater storage.
The research work was carried out at Kyera Farm, a training centre for organic farming near Mbarara, Uganda. Three sample tanks were developed at the farm and then ten tanks were built in the nearby village of Kyera. A study is now under way to look at the benefits that such small tanks can bring to the users.
Indications from a similar study in western Uganda show that up to 70% or 80% of household water needs can be met with small rainwater jars. Rainwater harvesting works best when rainfall is fairly regular through the year.
Water supply from the rain
Rainwater harvesting, or collection, is common in many parts of the world. Water is usually captured from the roof of a house and used for drinking, cooking, washing clothes, personal hygiene, watering plants and animals, and numerous other uses. Typical traditional methods of catching the water vary from small buckets to large tanks. Old oil drums are commonly seen outside homes in Uganda using short lengths of home-made guttering to catch the water.
Small jars are useful in areas where there is a good distribution of rain throughout the year, with two rainy seasons. The householder may still have to collect water from the traditional water source during the drier periods, but for much of the year, the family members will have water at the home. This can save a significant amount of time and effort in water collecting.
A study in Kabarole District, Uganda, during the dry season, showed that with just twelve rainy days in two months, a family of five could obtain 60% of all their household water from the tank – a total of 118 jerry cans (of 20 litres each). If their traditional water source was 500 metres away, in two months they would save nearly 50 hours of their time by using the water tank.
The quality of water from a rainwater system is an important concern. Usually, if water is filtered as it enters the tank and stored in dark conditions, then the quality of the water will be good and will improve with time. It is also recommended that during the first five minutes of heavy rainfall after a dry spell, this water is discarded by pushing the down pipe aside. All openings should be covered with mosquito mesh to prevent mosquitoes from breeding in the tank. Given good rainfall, one side of the roof of a typical dwelling will provide sufficient collection area to provide the household needs of an average family.
Costs
This table shows the approximate costs of the different jars:
|
Type |
Size |
Cost |
Cost |
|
|
(litres) |
(£) |
($) |
|
Brick jar |
750 |
£33 |
$50 |
|
Ferro-cement jar |
500 |
£28 |
$42 |
|
Plastic tube jar |
600 |
£20 |
$30 |
Costs of gutters are not included.
Local production
Local masons were involved as fully as possible so that they could share their knowledge with the project team, and also learn about the new designs. It was hoped that the masons would then go on to build other jars in the area and would also be able to maintain the systems already built. A good pool of skilled masons was found in the area. Three tanks were designed, each using slightly different techniques and materials.
Galvanised iron sheet gutters and down pipes are available in Mbarara town and these were used on all the jars that were built under the project. Alternative gutter systems can be used, of course (for example: bamboo).
Future work
Already masons are building these new jars for individuals in the area. A local women’s group has approached Kyera Farm staff with a request to build a number of jars. The local farmers group which benefited from the initial jars has received a flood of new members specifically interested in building these jars.
Readers who would like detailed construction plans, either on paper or by e-mail, should contact the DTU (see below).
Mr Dai Rees works in the Development Technology Unit, School of Engineering, University of Warwick, Coventry, CV4 7AL, UK. The drawings were provided by Vince Whitehead.
Tel: +44 (0)24 7652 2339 Fax: +44 (0)24 7641 8922 E-mail: dgr@eng.warwick.ac.uk Website: www.eng.warwick.ac.uk /DTU/rainwaterharvesting/index.html
The brick jar
The brick jar was developed to make use of this common local building material. The jar is made from a simple brick cylinder. A tap brings water out at the right height for a jerry can. The cover is made from ferro-cement mortar and a filter basin is used as described for the ferro-cement jar. It is a good idea to include some reinforcements in the brickwork, such as bands of wire.
The plastic tube tank
Plastic sheet in tube form is available in the local marketplace. A hole is dug in the ground, inside which the largest size of the plastic tube sheeting available can sit comfortably. The end of the plastic tube is folded and tied several times to form the seal. Two layers of plastic are used in case one should puncture. A surrounding brick wall is built, an overflow and low-cost handpump fitted and a basin used, as with the two other examples.
The ferro-cement jar
This design is already well known. The technology involves using chicken wire sandwiched between layers of cement mortar. A shaped mould is made from sacks and filled with sawdust. The mould is then plastered with sand/cement paste in a ratio of 3:1. This is then covered with 1/2" chicken wire and given a second coat of mortar. A tap and overflow are fitted and a plastic basin used to form the opening at the top – a filter is fitted here to remove large particles from the water. The jar is raised above the ground so that jerry cans can be filled easily from the tap.