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There are two main approaches to drilling boreholes: drilling with a mechanised rig; and manual drilling. The most appropriate technique will depend on the hydrogeology, the required yield, and available funds.
An introduction to borehole drilling techniques that are appropriate for rural water supply can be found in the chapter Designing and Constructing Water Points in MacDonald et al. (2001), which can be freely downloaded online.
Drilling with a rig
Most boreholes are drilled using a motorised drilling rig. There are different types of drilling rig and methods of drilling, and these should be chosen to suit the local hydrogeology. The main types are cable tool percussion (also known as shell and auger), and rotary drilling. Rotary drilling can be air flush, sometimes with down-the-hole hammer; mud flush; or reverse circulation.
Manual drilling is an approach that is appropriate in some hydrogeological environments, particularly in shallow unconsolidated aquifers with shallow water tables. It can reduce drilling costs and increase cost-effectiveness of groundwater development programmes. Manual drilling methods are being used to provide water for drinking and other domestic needs in at least 36 countries around the world, and in some places are already well established.
UNICEF has worked with a range of partners to develop a toolkit for African countries wishing to embark on the professionalisation of manual drilling. This toolkit includes technical notes and technical manuals, advocacy materials, case studies, and implementation and training manuals for manual drilling. There is also a series of mapsshowing areas suitable for manual drilling in 12 countries in West Africa, and a report on the mapping methodologies used.
The Rural Water Supply Network (RWSN) has produced a Manual Drilling Compendium, which provides a useful overview of the impacts and challenges of manual drilling, and support for improving practices on the ground.