artesian well

{{Short description|Confined aquifer containing groundwater under positive pressure}}

{{For|the water source in Australia|Great Artesian Basin}}

[[Image:Artesian aquifer scheme.svg|thumb|right|300px|Artesian aquifer scheme: {{olist

|Aquifer

|Impervious strata

|Infiltration area

|Artesian well

|Saturation level

|Subartesian well

|Artesian spring

}}]]

File:Artesian Well.svg giving rise to an artesian well]]

Image:Artesian Well (PSF).png

File:US Navy 091231-N-1572M-001 Seabees tap new water well.jpgs tapping an artesian well in Helmand Province, Afghanistan]]

An artesian well is a well that brings groundwater to the surface without pumping because it is under pressure within a body of rock or sediment known as an aquifer.{{Cite web|title=Artesian Water and Artesian Wells|url=https://www.usgs.gov/special-topic/water-science-school/science/artesian-water-and-artesian-wells?qt-science_center_objects=0#qt-science_center_objects|access-date=2020-12-18|website=www.usgs.gov|publisher=United States Geological Survey}} When trapped water in an aquifer is surrounded by layers of impermeable rock or clay, which apply positive pressure to the water, it is known as an artesian aquifer. If a well were to be sunk into an artesian aquifer, water in the well-pipe would rise to a height corresponding to the point where hydrostatic equilibrium is reached.

A well drilled into such an aquifer is called an artesian well. If water reaches the ground surface under the natural pressure of the aquifer, the well is termed a flowing artesian well.{{Citation | author1=Wheeler, H. W | title=Artesian bores of South Australia : an annotated photographic record, 1939-1948 | date=1980 | publisher=Pioneer Books | isbn=978-0-908065-06-6 }}{{Citation | author1=Federal Water Resources Assistance Program (Australia) | author2=New South Wales. Department of Water Resources. Technical Services Division | author3=Australian Water Resources Council. Interstate Working Group on the Great Artesian Basin | title=Specification for construction, reconditioning or plugging of bores tapping recognised aquifers of the Great Artesian Basin in New South Wales | date=1990 | publisher=Dept. of Water Resources, Technical Services Division | edition=1st | url=http://trove.nla.gov.au/work/6766983 | access-date=19 January 2014 }}

Fossil water aquifers can also be artesian if they are under sufficient pressure from the surrounding rocks, similar to how many newly tapped oil wells are pressurized.

File:Artesian well Virttaa.JPG, Finland]]

Not all aquifers are artesian (i.e., water table aquifers occur where the groundwater level at the top of the aquifer is at equilibrium with atmospheric pressure). Aquifers recharge when the water table at its recharge zone is at a higher elevation than the head of the well.