aquifer

A body of permeable rock or sediment that holds and transmits groundwater — the underground reservoir from which wells draw and springs emerge. Aquifers can be shallow or deep, confined between impermeable layers or open to the surface. The Ogallala Aquifer underlies 174,000 square miles of the Great Plains; the agricultural economy of the American interior depends on it, and it is being drained faster than it recharges. An aquifer is invisible wealth — water banked in stone.