Boreholes have many purposes: in oil drilling, geological survey and extracting water for irrigation and drinking. A hole bored for a well is usually cased by a vertical pipe to prevent the hole sides from collapsing and blocking the borehole. Wells can be bored with hand-operated machinery such as augers, which are drilled into the ground by steel rods and handle and usually are best for soft ground. Sometimes percussion drilling, such as with a steel hammer, is required for harder ground, whereby a tripod supports the tool on a cable which is lifted up and dropped down to loosen the soil. This technique is best for breaking hard and heavier ground and for reaching deeper down to a low water level when hand-digging would not be possible. This is a more expensive method than a hand-dug well. Engine driven drills go faster to reach the deepest water, but powerful electric pumps are required to extract the water at such depths. They can drill to hundreds of metres.
Hand dug wells
Hand-dug wells are the most common method of extracting groundwater in rural areas of the developing world. Wells can vary in depth depending on how deep the water is below the ground surface. Water is obtained either by a bucket and pulley or with a handpump. The location and construction of hand-dug wells depends on the stability of the ground; for example, ground consisting of sand or gravel can collapse while being dug. Clay type ground may be excavated without supporting the sides of the excavation, but wells in less stable ground are lined with materials such as concrete, masonry and brickwork to prevent collapse. If the well is built on lower ground it will be closer to the underground water and thus is not so deep. The advantage of hand-dug wells is the community is often able to provide the unskilled labour, thus reducing costs. Although sometimes time-consuming to construct, hand-dug wells generally provide good yields of water at lower costs than more sophisticated methods of water extraction. These wells can be constructed to a depth of, say about, 7 meters beyond which a borehole is required.
Handpumps, as a means for collecting water from a well, are generally preferable to using a bucket and rope. This is because they allow the well to be covered by a sealable slab, meaning less debris can enter the well, and so are particularly beneficial for drinking water. There are various types of pump, designed to reach different depths of water. For example lift pumps, which are the most common type, are used for shallow wells of up to, say, 7 metres deep and are fairly cheap and easy to maintain. Heavier duty pumps, on the other hand, work up to about 45 metres and are designed to reduce the physical effort required for pumping, and are more robust. The most powerful hand pumps can lift water from a depth of 90 metres. The type of pump a well needs depends on the depth of water below ground level, the output required, the availability of spare parts and local preference.
Gravity Water Systems
In this method, water flows downhill from a source, using gravity, through a system of pipelines, and tanks to tapstands within a local community. A source for a gravity-fed system may be an unpolluted spring or stream, a catchment area, or a purpose-made dam in a river or stream. This type of system means water is easily accessible to all households, schools and medical centres in a community. It provides a constant, reliable and sustainable water supply. These systems have low maintenance needs. They may initially have higher capital costs than other schemes, however running costs are relatively low. The work of carrying water is done away and allows the community to get on with looking after homes and crops.
There are various ways in which water can be extracted from a spring source, where groundwater emerges at the surface. A spring source can be used either for supplying a gravity-fed scheme, or for providing a single outlet with continuous water flow. The spring must be protected from pollution, so a spring collection chamber must be built around it, which is generally easy and cheap to construct. After vegetation above the spring is cleared and water temporarily diverted, large stones are placed above the head of the spring, topped with gravel and, which is all held in place by a cement wall with an outlet pipe for the water to flow out. This type of scheme is beneficial due to its low maintenance costs and good water quality, though in periods of drought the yield can diminish or dry up.
Rainwater can be some of the cleanest available, and so provides a good opportunity for water collection before it becomes contaminated. Rainwater harvesting is a technique whereby rain is collected and stored after running off surfaces which it has directly fallen upon. Commonly, rooftop harvesting is used, with tiles or corrugated steel being preferable roofing materials. The rainwater is collected in guttering around the eaves of a building, which transports the water into a storage tank. A mesh is placed at the end of the pipe before the water enters the tank to take out any roof debris such as leaves and sticks. Rainwater harvesting is most applicable to areas with one or two wet seasons per year, and is particularly advantageous due to its relatively cheap set-up and maintenance costs and the reduced need for water treatment if the collection surfaces are clean. Although boiling before consumption is always recommended. The larger the collection surface area the better and school roofs are often used.
Water Storage Tanks
Water storage tanks exist in several different forms; those which are elevated, those at ground level, and those below ground. Elevated tanks do not require the operation of pumps, as water flow is maintained by gravity. Surface level tanks take many forms, in various materials, and require regular maintenance to the exterior, but are beneficial for a smaller demand for water at the household level. Below-ground tanks are particularly advantageous in terms of conserving space above ground, and weathering is also eliminated. They are, however, more expensive to build. Tanks can be constructed in concrete, masonry and brick and lined with a water proof render. Tanks can be bought in plastic and steel in various sizes, normally in the range of 5 to 20,000 litres.
As a means of water harvesting, sand dams can provide a clean and local water supply at low cost and low maintenance. A concrete or stone dam is constructed across a river channel to trap sand, gravel and boulders washed downstream during the rainy periods. It normally takes 3 to 5 years for the area behind the dam to fill up to the lip of the dam. The volume of the debris behind the dam can retain up to 35% water. Water is obtained by digging down into the area behind the dam. Also a steel pipe can be built into the base of the dam and a tap fitted to the pipe on the outside of the dam. The presence of water behind the dam can elevate the water table in the general area and crops can be grown on the sides of the dam and on the surface behind the dam. Outside expert knowledge is needed for these projects (such as from our partner the Africa Sand Dam Foundation), but once constructed a sand dam can provide a year-round source of water.
The single pit latrine is one of the most commonly used sanitation technologies. Excreta and cleansing materials are deposited into a pit, which can be lined with materials such as brick, concrete, stones or timber to prevent it from collapsing. Leaching and degradation limit the rate of accumulation in the pit: liquids percolate into the soil through the bottom of the pit and walls, and microbial action degrades the organic matter. Pits are usually designed to contain at least 1,000 litres, meaning they may last up to 20 years without emptying. Latrines are typically built more than 30m away from a water source to prevent contamination. Pit latrines have the advantage of not needing a constant source of water and tend to have low capital costs. However, they may still pose some health risks and flies and odour are normally an issue. Ventilated improved pit (VIP) latrines may be preferable, as explained below.
Ventilated Improved Pit (VIP) Latrines
A VIP latrine improves on the normal pit latrine in that it enables continuous airflow through a pipe which vents odours and traps flies. Flies that get into the pit are attracted to the light at the top of the ventilation pipe, where they are then trapped by the fly-screen. The vent pipe works most effectively in windy areas, or when the pipe is painted black to create an updraft due to the heat difference between the pit and the vent. It must be ensured that flies are not attracted to light through the defecation hole, by having a simple removable cover for the hole, normally wooden. A double VIP latrine can also be used, where a second pit’s contents can rest, degrade and reduce in volume while the other is in use. The content of the unused pit reduces to compost after about 6 months and can be used for agriculture. The pit not in use should be covered and sealed, and both pits should be well lined to ensure longevity.
Communal latrines are mostly very similar to individual pit latrines, but are larger and serve more people (though have a certain group of private users, unlike a public toilet block). Various sanitation systems can be used, including simple pits, flush latrines and septic tanks. The design must consider having separate male and female facilities, appropriately designed facilities for children and people with physical disabilities. They are usually made from locally available materials. Being communal means that they also must be maintained in an agreed way by the users. These schemes work well with effective community leadership, whereby a community-elected management team runs them. They are also ideal in densely populated areas where space for individual latrines is limited.