- A geologic formation, a group of formations, or a part of a formation that is water bearing.
- A geological formation or structure that stores or transmits water, or both, such as to wells and springs.
- An underground layer of porous rock, sand, or gravel containing large amounts of water. Use of the term is usually restricted to those water-bearing structures capable of yielding water in sufficient quantity to constitute a usable supply.
- A sand, gravel, or rock formation capable of storing or conveying water below the surface of the land.
- A geologic formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs.
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