Editing Aquifer (section)

== Properties ==
{{See also|Aquifer properties|}}

=== Depth ===
[[File:Aquifer en.svg|thumb|right|An aquifer cross-section. This diagram shows two aquifers with one aquitard (a confining or impermeable layer) between them, surrounded by the bedrock ''aquiclude'', which is in contact with a gaining [[stream]] (typical in [[humid]] regions). The water table and [[vadose zone|unsaturated zone]] are also illustrated.|upright=1.6]]
Aquifers occur from near-surface to deeper than {{convert|9000|m|ft}}.<ref>{{cite web | url = https://www.usgs.gov/special-topic/water-science-school/science/aquifers-and-groundwater | title = Aquifers and Groundwater | work = USGS | quote = ...more than 30,000 feet. On average, however, the porosity and permeability of rocks decrease as their depth below land surface increases; the pores and cracks in rocks at great depths are closed or greatly reduced in size because of the weight of overlying rocks.}}</ref> Those closer to the surface are not only more likely to be used for water supply and irrigation, but are also more likely to be replenished by local rainfall. Although aquifers are sometimes characterized as "underground rivers or lakes," they are actually porous rock saturated with water.<ref>{{Cite web|date=2019-07-30|title=Aquifers|url=http://www.nationalgeographic.org/encyclopedia/aquifers/|access-date=2021-09-17|website=National Geographic Society|language=en}}</ref>

Many desert areas have [[limestone]] [[hills]] or mountains within them or close to them that can be exploited as groundwater resources.<ref>{{Cite web |title=Types of aquifers: Aquiclude, Aquitard and Aquifuge and location of aquifers – Geography of Water Resources |url=https://ebooks.inflibnet.ac.in/geop16/chapter/types-of-aquifers-aquiclude-aquitard-and-aquifuge-and-location-of-aquifers/ |access-date=2024-06-27 |website=ebooks.inflibnet.ac.in}}</ref> Part of the [[Atlas Mountains]] in North Africa, the [[Mount Lebanon|Lebanon]] and [[Anti-Lebanon]] ranges between Syria and Lebanon, the [[Jebel Akhdar (Oman)|Jebel Akhdar]] in Oman, parts of the [[Sierra Nevada (U.S.)|Sierra Nevada]] and neighboring ranges in the [[Southwestern United States|United States' Southwest]], have shallow aquifers that are exploited for their water. [[Overexploitation]] can lead to the exceeding of the practical sustained yield; i.e., more water is taken out than can be replenished.

Along the coastlines of certain countries, such as [[Libya]] and Israel, increased water usage associated with population growth has caused a lowering of the [[water table]] and the subsequent [[Saltwater intrusion|contamination of the groundwater with saltwater]] from the sea.

In 2013 large freshwater aquifers were discovered under continental shelves off Australia, China, North America and South Africa. They contain an estimated half a million cubic kilometers of "low salinity" water that could be economically processed into [[Drinking water|potable water]]. The reserves formed when ocean levels were lower and rainwater made its way into the ground in land areas that were not submerged until the [[ice age]] ended 20,000 years ago. The volume is estimated to be 100 times the amount of water extracted from other aquifers since 1900.<ref>{{cite web |url=http://www.gizmag.com/freshwater-reserves-under-sea/30072/ |title=Huge reserves of freshwater lie beneath the ocean floor |publisher=Gizmag.com |date=11 December 2013 |access-date=15 December 2013}}</ref><ref>{{Cite journal |last1=Post |first1=V. E. A. |last2=Groen |first2=J. |last3=Kooi |first3=H. |last4=Person |first4=M. |last5=Ge |first5=S. |last6=Edmunds |first6=W. M. |doi=10.1038/nature12858 |title=Offshore fresh groundwater reserves as a global phenomenon |journal=Nature |volume=504 |issue=7478 |pages=71–78 |year=2013 |pmid=24305150 |bibcode=2013Natur.504...71P |s2cid=4468578 }}</ref>

===Groundwater recharge===
{{excerpt|Groundwater recharge|paragraphs=1|file=no}}