Groundwater

Groundwater is the water that seeps into the earth and is stored in aquifers—areas of soil, sand, and rock that are capable of holding liquid. The water sits in between particles or in cracks and fissures. These saturated underground areas—some replenished by rain and snow, others not—can be found close to the Earth’s surface or hundreds of feet underground.

When you pass a natural spring spilling water from a mysterious source, that source is often groundwater. This underground H20 also makes its way into lakes and rivers and is often tapped by wells for drinking and irrigation supply.

Nearly 50 percent of people living in the U.S. get their drinking water from groundwater. But its biggest use is irrigation.

Threats to this underground source increase as population and development accelerate. Agricultural and urban runoff tainted with chemical pesticides and fertilizers seeps into groundwater sources, as does gas from leaking underground tanks. But the biggest threat? Overtapping this limited resource.

Taxed by political, economic, and development pressures, some groundwater sources are now facing depletion. The solution may rely on cooperation, often across political borders, and better management policies.

Fast Facts

• The overpumping of groundwater is causing water tables to fall across large areas of northern China, India, Pakistan, Iran, the Middle East, Mexico, and the western United States.

• The United States is the world’s third largest irrigator (after China and India).

• The Ogallala Aquifer, which spans parts of eight states from southern South Dakota to northwest Texas, is steadily being depleted. The Ogallala provides 30 percent of the groundwater used for irrigation in the U.S., and as of 2005, a volume equivalent to two-thirds the water in Lake Erie had been depleted.