Aquifers, wells, recharge, discharge, springs, water table, soil, rock pores, drinking water, irrigation, contamination, pumping, drought, and the water cycle
Groundwater
Groundwater is water stored below Earth’s surface in the pores and cracks of soil, sand, gravel, and rock.
What it means
Groundwater is water beneath the land surface. It occupies the tiny spaces between grains of sand and gravel, the cracks in rock, and the connected pores of aquifers. It is hidden, but it is not separate from the rest of the water cycle.
How it gets there
Some rain and snowmelt run off into streams. Some evaporates or is taken up by plants. The rest may soak downward through soil, a process called infiltration. When that water reaches saturated material underground, it becomes groundwater.
Aquifers and wells
An aquifer is a body of rock or sediment that can store and transmit usable amounts of groundwater. Wells tap aquifers by creating a path for water to be pumped upward. A productive aquifer needs both storage space and connected pathways for flow.
The water table
The water table is the upper surface of the saturated zone in an unconfined aquifer. It can rise after wet periods and fall during drought or heavy pumping. In some places it is close to the surface; elsewhere it may be hundreds of feet down.
Groundwater moves
Groundwater usually moves slowly from recharge areas toward discharge areas. It may feed a spring, seep into a stream, flow toward the coast, or remain underground for a long time. The direction and speed depend on pressure, slope, rock type, and permeability.
Quality risks
Because groundwater moves through soil and rock, some pollutants can be filtered or transformed. Others persist. Leaking tanks, septic systems, fertilizers, industrial chemicals, road salt, mining, and natural minerals can all affect groundwater quality.
Pumping and depletion
Groundwater can support drinking water, farms, industry, and ecosystems, but pumping faster than recharge lowers water levels. Long-term depletion can dry wells, reduce streamflow, raise pumping costs, invite saltwater intrusion near coasts, or contribute to land subsidence.
Why it matters
Groundwater is easy to ignore until a well runs low or contamination appears. Protecting it requires patience: prevent pollution before it enters the ground, track water levels, manage pumping, and remember that surface water and groundwater often trade water back and forth.