|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)|
|Part B - Technology profiles|
|2. Domestic water supply|
|2.1 Fresh water augmentation technologies|
Handpumps tap groundwater from shallow or medium depth aquifers and from deep aquifers if the at rest water level is high enough. Handpumps are water conveyance systems used to bring groundwater to the surface. There are a number of such pumps in operation in Africa and numerous textbooks provide specific descriptions of these devices (Figure 31).
Figure 31. Some commonly used handpumps.
In normal circumstances, handpumps are installed in wide diameter wells, which can be constructed by hand to depths of up to about 15 m, or drilled by rigs to much greater depths. The type of well most widely used is the hand-dug well, which is one of the cheapest means for providing a small supply of water in rural areas. A depth of about 10 to 20 m is usually considered the limit of practical manual sinking. The diameter of the well should not be less than 1.2 m, allowing two persons to work together in the well. A lining, that serves several purposes, should be used as the well is sunk. The lining is a protection during construction against caving and collapse, and retains the well wall after completion. There are many materials suitable for linings; e.g., masonry, brickwork, and plain or reinforced concrete. On the bottom of the well, it is usual to place a filter of graded layers of gravel to prevent the ground material from being drawn upwards into the well with the water. At the surface, the lining of the well should be raised at least 0.6 m above ground level and provided with a protection platform to channel drainage away form the well,
Small diameter wells may also be constructed by means of an auger. The auger, which is usually about 100 mm across, may be rotated by hand. Mechanised augers, or power augers, are also available. Once the water-bearing layer has been penetrated, the necessary length of piping, tipped with a screened wellpoint, or strainer, is lowered into the hole; a pump attached to its upper end, and the well “cleared” by pumping.
Tube wells consist of a perforated or screened pipe which is jetted or driven into the groundwater-bearing aquifer. Tube wells can yield large quantities of water, but the depth to which they can be driven is limited and the ground formation must be appropriate for their use. Their most common application is in the extraction of groundwater from water-bearing sands, especially those forming the beds of ephemeral streams. Tube wells can also be installed in perennial rivers, making use of the natural filtering properties of sandy beds of the rivers by drawing water through the river beds instead of from the rivers themselves. The pipes are usually 25 to 100 mm in diameter. The wells constitute a good means of obtaining water from areas with relatively coarse sand.
Extent of Use
Wells using handpumps are extensively used throughout Africa.
Operation and Maintenance
The operation and maintenance of handpumps varies depending on the type and complexity of the pump. Attempts at designing a reliable pump which can be maintained at the village level continue. Experimentation with these village level operation and maintenance (VLOM) schemes are shifting gradually to focus on institutional-level operation and maintenance. Preventative maintenance operations carried out by villages and institutions include greasing moving parts (taking care not to contaminate the water supply with oils and greases), tightening bolts, replacing seals (for some pumps), and cleaning the surroundings.
Level of Involvement
Local inputs to implementation of this technology are generally in terms of skilled labour and materials. Technical advice may be necessary in the conduct of hydrogeological investigations and well drilling.
While hand dug wells are quite inexpensive, boreholes drilled by rigs are fairly expensive in terms of initial capital costs. Dug shallow wells and augured tube wells have a per capita construction cost of $6 to $20, with an operation and maintenance cost of $0.02 to $0.14 per capita per year. Machine-drilled boreholes, equipped with a hand pump and serving a population of about 200 to 300 people, will have an estimated per capita construction cost of $19 to $23, and an operation and maintenance cost of $0.26 to $0.52 per capita per year.
Effectiveness of the Technology
The delivery rate of most handpumps is around 20 l/min, and their ease of operation makes them ideal for rural operations.
Dug wells are an appropriate option in areas where groundwater is less than 20 in below ground level. Augured tube wells, dug using motorised and/or manual rigs and augers of limited penetration, are appropriate in areas in which groundwater occurs at depths between 20 and 35 in. Motorised, conventional drilling rigs are an ideal means of developing water supply sources in areas where groundwater occurs at depths greater than 35 m below ground level, or in hard rock between 20 and 25 m depth, where the weathered material is thin.
The existence of a well may lead to increased erosion in its immediate vicinity. However, wells are focal points for other development such as the planting etc.
Well water is relatively safe without treatment. Hand dug wells are inexpensive and can be constructed using local skills and materials; community participation is easy to organize. Further, the operation of handpumps requires no external power and few skills, and the pumps may be maintained by local technicians. The use of spare parts is small.
The capacity of a well is limited, and service supply levels are lower than in piped schemes supplied from conventional sources. Hand dug wells are reliable only in areas where good quality groundwater is available at shallow depth. The hygienic quality of the wells, especially shallow wells, is not always satisfactory as a result of surface water intrusions leaking through the slab and superstructure, and around the pump casing.
There are no cultural problems in utilizing groundwater for domestic purposes. However, communities do not like wells to be developed too close to sacred places such as shrines.
Further Development of the Technology
There is need to improve on the methods of digging the shallow wells. Also, the handpump needs further developmental work to make it more suitable for village level operation and maintenance. Maintenance systems require further development to ensure sustainability.
Further information can readily be obtained from the Departments of Water in the various countries, and also from organisations such as UNICEF, World Vision, CARE, and Save the Children, among others.