DEFINITION of 'Groundwater'

Water that is found underground rather than on the surface. Groundwater is created when rain seeps into the ground through permeable surfaces rather than evaporating into the atmosphere. It can be accessed through wells drilled or dug into the ground.

BREAKING DOWN 'Groundwater'

Groundwater is used as the primary water source for many people, especially those living in rural areas. The U.S Geological Survey estimates that half of the United States use groundwater. Groundwater is used to provide water to people. It is also used by farmers to water crops and ranchers to provide water to livestock. 

Chemicals and pollutants that are dissolved in water at the surface can filter into groundwater reservoirs, such as aquifers. This poses a substantial environmental threat because the chemicals can affect the health of those drawing on groundwater sources. Polluted groundwater can have a substantial economic impact if livestock become sick or farmland polluted. Stationary sources of pollution include landfills and lined ponds for wastewater, while spills of hazardous chemicals can also pose threats.

The development and increased use of hydraulic fracturing (“fracking”) to gain access to underground sources of oil and natural gas has brought renewed focus to groundwater threats. Fracking uses pressurized chemicals and water to break into underground reservoirs. Much of the water used in this process remains underground as the reservoir is depleted, but a portion is brought up to the surface. This water must be treated in order to be safe, but groundwater supplies can become unsafe and unusable if untreated water seeps back underground.

In some areas unrestricted use of groundwater by farmers has led to a depletion of groundwater resources, which causes significant problems during drought conditions. Some states, such as California, have historically considered a private natural resource rather than one owned by the public, allowing farmers and landowners to extract as much water as they wanted.