Aquifer is the name given to a geological formation that contains water in sufficient quantity to supply wells. The water may be contained in nonconsolidated gravel, in porous or cracked rock or in underground caves. The amount of water that can be drawn from an aquifer varies from less than a gallon per minute for watering cattle in the desert to thousands of gallons per minute for supplying the domestic and industrial needs of a town.
In some parts of the world aquifers contribute significantly to the natural water reserves. There are large aquifers in several regions of the USA, for example, the sand and gravel formations in the South Eastern coastal plains stretch for hundreds of miles and are several hundred feet thick.
Aquifers are a valuable natural reservoir for the storage of large amounts of water and do not suffer the evaporation losses of surface waters. Care has to be taken not to draw too much from the reserve. Dangers of overpumping are seepage into the aquifer of saline water, and subsidence causing damage to wells and to surface structures.