Wells are drilled for many reasons. To take water levels (observation or piezometer wells), obtain water samples (monitoring wells), recover contaminated water and/or free product (recovery wells), wells installed to lower water levels (dewatering wells), and wells used to pump abundant amounts of potable water (supply or production wells).
Diameter of the well is often determined by use of the well or how much water is needed, which is influenced by size of the pump. As a rule of thumb, doubling well diameter only provides 10% more water (i.e., increasing the diameter from 6 to 12 inches only adds 10% to well yield). Most of this increase is due to increased well efficiency and less friction at the screen due to lower velocities and ability of the formation to provide water remains constant.