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Groundwater: What is Groundwater?
Groundwater originates as rain or snow. As precipitation falls on the earth's surface, some evaporates, some runs
off over land into lakes and streams and some soaks into the ground. A portion of water that enters the soil is
taken up and used by plants. (A large, leafy tree can take up a ton of water in a day!) The rest percolates deeper
into the earth.
Not all water found in the ground is groundwater. "Groundwater" refers specifically to water that is held in the
saturated zone below the water table. Rock and soil material stores water in spaces, much like a sponge.
Imagine two sponges, stacked one on top of the other. The bottom sponge has been soaked in water. It represents
the "saturated zone"--all of its pore spaces are filled with water. The top sponge has been wetted, but the water
has been squeezed out. This sponge represents the "unsaturated zone"--some of the spaces are filled with water,
some are filled with air. The boundary between the two zones represents the "water table." The water in the
saturated sponge represents groundwater.
(Resource: WDNR Study Guide)
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