Groundwater Extraction: The Pros and Cons!

A water borehole is not just a hole in the ground. It has to be properly designed, professionally constructed and carefully drilled. Boreholes for extracting water consist essentially of a vertically drilled hole, a strong lining to prevent the collapse of the walls, which includes a means of allowing clean water to enter the borehole space (screen), surface protection, and a means of extracting water. Drilling by machine is an expensive process, and boreholes require professional expertise for both their design and their construction. There are, however, compensations: this method of extracting water has a number of significant advantages.

The common alternatives to drilled boreholes, available to everyone with basic knowledge and simple tools, are surface water sources, springs, and dug wells. Where shallow groundwater emerges at a seepage site or at a spring, water catchment systems can be constructed to provide water of reasonable quality. Catchments, that include sand or stone filters, and collector sumps are extremely effective means of collecting water. Gravity may be used to affect pipe network distribution from upland springs. Shallow-dug wells usually exploit near-surface groundwater. Wells down to a depth of five metres are relatively simple to construct (given time and willing local labour), and there are many publications describing this process. Furthermore, because of their relatively large diameter, wells provide valuable storage volume. The water supply can be protected by lining the well, covering it with a lid, and fitting a hand pump to it.

However, dug wells, and surface water catchments in general, are very vulnerable to contamination caused by agricultural activities, animals, poor sanitation and refuse. In addition, surface or shallow groundwater catchment is vulnerable to poor rainfall and declines in water level caused by drought, because it usually taps the top of the aquifer. Borehole water, by contrast, often requires no treatment and is less susceptible to drops in water levels during periods of drought or limited rainfall.

Advantages of drilled boreholes

If they are properly designed and maintained, drilled boreholes:

•  Are less vulnerable to drought or drops in water level when drilled into deep water-bearing formations.
•  Can be designed to exploit more than one aquifer (when individual aquifers are vertically separated and not hydraulically connected)
•  Are less vulnerable to collapse
•  Are less vulnerable to contamination
•  Are, if properly sited, capable of producing large yields; so, mechanically or electrically powered pumps can be used
•  Are amenable to quantitative monitoring and testing, which enables accurate assessment of aquifer parameters (as in aquifer modelling), water supply efficiency, and optimal design of pump and storage/distribution systems
•  Can be used to monitor groundwater levels for other purposes, e.g. environmental studies or waste disposal

– Disadvantages of drilled boreholes

•  High initial material costs and input of specialized expertise, i.e. construction, operation, and maintenance may require skills and expensive heavy equipment.
•  Vulnerable to irreversible natural deterioration if inadequately monitored and maintained
•  Vulnerable to sabotage, can be irreparably destroyed with little effort if inadequately protected
•  Require a source of energy if water extraction pumps are used (unlike gravity feed systems)
•  Do not allow direct access, for maintenance or repairs, to constructed parts that are underground