2.1.9 Cisterns

Technical Description

Cisterns are an ancient method of water harvesting, dating back to the early Roman empire. There are artificial reservoirs constructed by excavating bedrock, such as limestone, to depths of between 3 and 7 metres to provide water storage throughout the Roman world. While serving a similar purpose, modern cisterns are usually built with cement blocks or fired bricks.

Cisterns collect water in the form of runoff from a rock-lined catchment or other suitable, nonporous surface. There is commonly a settling basin at the cistern entrance which serves to settle sediments borne by the runoff. A screen is also provided to remove larger particulates.

Extent of Use

This technology is used in a number of north African countries, where it is known by a variety of different names. These names are indicated in brackets. The technology is used in Libya (where it is known as Fusqia or Majen), Algeria (Sahrij), Egypt (Roman reservoir), Tunisia (Fuskia pool), Morocco (Al Majel), and Sudan (ground reservoir).

Operations and Maintenance

Routine maintenance is necessary to reduce losses to leakage by repairing cracked walls. There is also a need for the periodic removal of sediments which might choke the entrance.

Level of Involvement

This technology can be constructed, operated and maintained by villagers.

Costs

The cost of implementing this technology is reasonably low, as most of the construction of the cisterns can be done by communities. However, mechanization is increasingly used for the digging of the cistern, which increases the cost.

Effectiveness of the Technology

The volume of water harvested depends on the amount of rainfall and the size of cistern. Major losses of water generally occur in the catchment area, through infiltration and evaporation, rather than from the cistern itself, provided the cistern is maintained.

Suitability

The technology is suitable for use in all regions of Africa and is similar to rock catchment systems. In areas of high evaporation, the cistern should be covered to minimize evaporative losses.

Environmental Benefits

The use of cisterns to capture runoff has no known negative environmental effects, and can provide water for a variety of environmental purposes in dry areas.

Advantages

This technology has the advantage of being a simple, low cost technology which can increase the yield of water from rock catchment systems.

Disadvantages

Use of this technology may require provision of an abstraction system to draw the water from the cistern. Because of the likelihood of contamination from surface sources, this technology is not ideal for use as a potable water source.

Cultural Acceptability

This technology is culturally acceptable by the communities in which it has been used.

Information Sources

UNESCO Regional Office for Science and Technology for the Arab States, Arab Centre for Studies of Arid Zones and Dry Lands (ACSAD) 1986. Regional Project on Rational Utilization and Conservation of Water Resources in the Rural Areas of the Arab States with Emphasis on the Traditional Water Systems, UNESCO Project ROSTAS/HYD/1/86.