Editing Water table (section)

{{Short description|Top of a saturated aquifer, or where the water pressure head is equal to the atmospheric pressure}}
{{For|the architectural feature|Water table (architecture)}}
[[File:Water table.svg|thumb|350px|Cross section showing the water table varying with surface topography as well as a perched water table]]
[[Image:Groundwater flow and infiltration diagram.svg|thumb|250px|Cross-section of a hillslope depicting the [[vadose zone]], [[capillary fringe]], water table, and the [[phreatic]] or saturated zone. ''(Source: [[United States Geological Survey]].)'']]

The '''water table''' is the upper surface of the [[phreatic zone]] or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with [[groundwater]],<ref>{{Cite web|url=http://imnh.isu.edu/digitalatlas/hydr/concepts/gwater/wattable.htm|title=What is the Water Table?|website=imnh.isu.edu|access-date=2016-11-25}}</ref> which may be fresh, saline, or brackish, depending on the locality. It can also be simply explained as the depth below which the ground is saturated. The portion above the water table is the [[vadose zone]]. It may be visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity.<ref name="groundwater">{{cite book |last1=Freeze |first1=R. Allan |first2=John A. |last2=Cherry |year=1979 |title=Groundwater |location=Englewood Cliffs, NJ |publisher=Prentice-Hall |isbn=9780133653120 |oclc=252025686}}{{page needed|date=February 2012}}</ref>

In coarse soils, the water table settles at the surface where the water [[Hydraulic head|pressure head]] is equal to the [[atmospheric pressure]] (where gauge pressure = 0). In soils where [[capillary action]] is strong, the water table is pulled upward, forming a [[capillary fringe]]. 

The groundwater may be from [[precipitation]] or from more distant groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths, water fills in more of the pore spaces in the soils, until a zone of saturation is reached. Below the water table, in the zone of saturation, layers of permeable rock that yield groundwater are called [[aquifer|aquifers]]. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define.

“Water table” and “[[water level]]” are not synonymous. If a deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in this aquifer may rise to a level that is greater or less than the elevation of the actual water table. The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the [[potentiometric surface]], not the water table.<ref name="groundwater" />