Aquifer [1]

A geological formation that contains water, especially water that supplies springs and wells.

Aquifers have become important in petroleum marketing operations because gasoline [2] and other products from leaking underground tanks [3] and piping can find their way into an aquifer that serves as the drinking water source for a community.

A sole-source aquifer is an aquifer that has been designated by the U.S. Environmental Protection Agency  [4]as one that constitutes the only, or principal, water supply source for a city or other community.