Many dry out for extended periods of time. Others may appear dry on the surface but are saturated underneath. These complex ecosystems play an important role in the health of our environment and the quality of our water. Beneath the land's surface, water resides in two general zones, the saturated and the unsaturated. The unsaturated zone lies directly beneath the land surface, where air and water fill in the pore spaces between soil and rock particles.
Water saturates the zone beneath the unsaturated one.
Half the drinking water in the United States comes from groundwater. This water is an important natural resource and used for many purposes, including drinking water, irrigation and livestock raising. Half the water used in the United States for drinking water comes from groundwater. Therefore, the unsaturated zone plays an important role in groundwater hydrology and may act as a pathway for groundwater contamination. Groundwater can move laterally and emerge at discharge sites, such as springs on hill sides, or seep in from the bottoms of streams, lakes, wetlands, and oceans.