Aquifer
From Swikipedia
Introduction
About 41 inches of average precipitation (both rain and snow) runs into lakes, rivers, ocean, or into underground storage areas called aquifers. Aquifers are underground reservoirs. They are underground layers of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. The water that reaches these chambers is usually much cleaner than the water of reservoirs at the earth's surface. Almost no bacteria live in aquifers. Many pollutants are filtered out as the water passes through the soil on its way to the aquifer.
The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. The surface of saturated material in an aquifer is known as the water table.
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