What is Groundwater?
Groundwater is the water that soaks into the soil from rain or other precipitation and moves downward to fill cracks and other openings in beds of rocks and sand. It is, therefore, a renewable resource, although renewal rates vary greatly according to environmental conditions.
It also is an abundant natural resource.
Of all the freshwater in the world (excluding polar ice caps), 95 percent is groundwater. Surface water (lakes and rivers) only make up three percent of our freshwater.
Groundwater’s Importance to the Environment
Hydrologists estimate, according to the National Geographic Society, U.S. groundwater reserves to be at least 33,000 trillion gallons — equal to the amount discharged into the Gulf of Mexico by the Mississippi River in the past 200 years.
At any given moment, groundwater is 20 to 30 times greater than the amount in all the lakes, streams, and rivers of the United States.
About a quarter of all U.S. rainfall becomes groundwater. Groundwater provides much of the flow of many streams; many lakes and streams are “windows” to the water table. In large part, the flow in a stream represents water that has flowed from the ground into the stream channel. It’s estimated by the USGS that about 30 percent of U.S. streamflow is from groundwater, although it is higher in some locations and less in others.
All the water of the Earth including the atmosphere, oceans, surface water, and groundwater participates in the natural system we call the hydrologic cycle. As water moves through all these elements repeatedly, the system is truly cyclical.