The supply of fresh water found beneath the earth’s surface (usually in aquifers) often used for supplying wells and springs. Because groundwater is a major source of drinking water, concern is growing over areas where leaching agricultural or industrial pollutants or substances from leaking underground storage tanks (USTs) are contaminating groundwater.

Subsurface water occupying a saturated geological formation from which wells and springs are fed.

Source: Handbook of water and wastewater treatment plant operations