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There are important considerations that will help determine if drilling a well is feasible, and how complex (and expensive) the process will be.

• If you are just getting started in an off-the-grid or rural project, before you even choose a location or purchase land, get a geological survey to identify locations where conditions are suitable for installing a well.
• The geological survey will help you determine the nature of the groundwater supply. Wells are easier to drill when the groundwater forms underground reservoirs, but this is a less common situation. More often, groundwater supplies exist in layers of porous sands and silts, and here the process of creating a well can be more difficult, though by no means impossible.
• Geo-survey also helps determine the depth of the groundwater supply. The depth of the groundwater supply may dictate how, and if, you can drill a well. In the semi-arid and arid regions of Kenya, acceptable water will usually require going at least 50 meters down, but better water will usually be even deeper.
• Water quality will also need to be assessed.  You cannot know exact quality of water until you test it, but the geo-survey should give you general parameters if the water in the area is potable.   
• In Kenya, a water permit is required since the quality of drinking water is a matter of public health.  The permit needs to be acquired before drilling begins.

It is difficult to visualize water underground. Some people think that the equipment used in a geological survey can identify the presence of water. This is not the case, electrical resistivity instruments measure cracks in the rocks and identifies places where water can accumulate. To locate groundwater accurately and to determine the depth, quantity, and quality of the water, several techniques must be used, and a target area must be thoroughly tested and studied to identify hydrologic and geologic features important to the planning and management of water resource.

The landscape may offer clues to the hydrologist about the occurrence of groundwater. In some regions–in parts of semi-arid Kenya, for example–the presence of “water-loving” plants are used identify groundwater at shallow to moderate depth. Rocks are the most valuable clues of all. The hydrologist prepares a geologic map showing where the different kinds of rock come to the land surface. Next, the hydrologist gathers information on the wells in the area—their locations, the depth to water, the amount of water pumped, and the kinds of rock they penetrate. If there are no wells in the area, or not enough information is available on existing ones, the hydrologist may not be able to guarantee water levels. The hydrologist’s report and geologic map will try to show where water can be found, its chemical composition, and in a general way, how much is available. This is the scientific approach used in a Geological Survey, if properly applied can be very effective.  W4W Kenya has a 90% success rate.

The main factors that determine the cost of a well are depth, soil formation, and location. It is also important to note that the cost of a well only includes the borehole and casing.  The pump, storage and distribution of the water is usually quoted separately.

The cost of drilling a well/borehole in Kenya typically ranges between $6,000 and $12,000. Expect to pay between $60 and $80 per meter of depth, or up to $100 for difficult terrain.  Mobilization cost will also be added to the quote.  The more remote the project the greater the mobilization cost.

Boreholes are drilled to function for a lifespan of 20 to 50 years. However, the lifespan of a pump maybe less.  The key to the longevity of a well is proper use and maintenance.

In most areas, groundwater is considerably purer than any other source, since it has been thoroughly filtered by the earth as rainwater slowly drains down into the water table. A groundwater well may also be the only practical way to obtain fresh water in a rural area.

Test pumping indicate the water-bearing properties of the aquifer tapped by the well. From the tests the hydrologist can determine the amount of water moving through the aquifer, the volume of water that can enter the well, and the effect of pumping on the water level of other wells in the area.  Water quality is also tested. The hydrologist will take samples of water from the well and have them chemically analyzed.  Test pumps are critical for developing the well and insuring its proper use.