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Answer: An aquifer is a place underground where groundwater is found in usable quantities. Groundwater occurs in the saturated soil and rock below the water table, and if the aquifer is shallow and permeable enough to let water move at a rapid-enough rate, people can drill wells into it and withdraw water.

How much water

There is about a hundred times more fresh water in the ground than is in all the world's rivers and freshwater lakes.

The water table

A hole dug at the beach shows how the ground, if permeable enough, can hold water. The upper surface of this zone of saturation is called the water table. Most of the void spaces in the rocks below the water table are filled with water. These rocks have different porosity and permeability characteristics, so water does not move the same way in all rocks below ground.

Recharge and discharge

Groundwater is a part of the natural water cycle. Some of the precipitation that lands on the ground infiltrates into the subsurface. The part that continues downward until it reaches saturated rock is groundwater recharge. Water in the groundwater system moves slowly and may eventually discharge into streams, lakes, and oceans.

Why the water table changes

The level of the water table can naturally change over time due to changes in weather cycles and precipitation patterns, streamflow and geologic changes, and human-induced changes such as more impervious surfaces on the landscape.

Claims

• id: C1 claim: The upper surface of the zone of saturation is the water table. source: S1 evidence: "The upper surface of this zone of saturation is called the water table."
• id: C2 claim: Usable groundwater is found only in certain places called aquifers. source: S1 evidence: "But it is only found in usable quantities in certain places underground — aquifers."
• id: C3 claim: Groundwater is part of the natural water cycle. source: S2 evidence: "Groundwater is a part of the natural water cycle"

Sources

• [S1] Aquifers and Groundwater. USGS. https://www.usgs.gov/special-topics/water-science-school/science/aquifers-and-groundwater . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Groundwater: What is Groundwater?. USGS. https://www.usgs.gov/special-topics/water-science-school/science/groundwater-what-groundwater . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_ycy5sv12,
  author = {{iinventedlight}},
  title = {{Aquifers: where usable groundwater is stored}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/aquifers/},
  note = {Permanent ID iil:note:ycy5sv12. License: CC-BY-4.0.},
}

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