Deep Wells:

A deep well is the one which rests on an impervious layer and draws its supply from the pervious formation lying below through a bore hole made into the impervious layer. The impervious layer may be of clay, cemented sand, kankar or other hard materials which are often found laying a few metres below the water table in the sub-soil. The impervious layer gives structural support to the open well resting on its surface. This impervious layer may be continuous or sometimes localized and can be of varying thickness.

These wells are frequently polluted through the surface openings. A newly constructed well, sometimes, shows pollution from the drilling operations, which carry surface matter into the well with tools.

Entrance of surface water should be entirely prevented by every known means. Well pits in which the pipe system is located should be so drained that neither storm nor sanitary water may back-up through the drains into the pits and enter the well. The well casing should extend around one meter above the floor. Because of the longer travel of ground water to reach pervious layer below the top impervious layer, deep well yields safer water than shallow wells.