An artesian aquifer is a confined aquifer containing groundwater under positive pressure. This causes the water level in a well to rise to a point where hydrostatic equilibrium has been reached. This type of well is called an artesian well. Water may even reach the ground surface if the natural pressure is high enough, in which case the well is called a flowing artesian well.

An aquifer is a geologic layer of porous and permeable material such as sand and gravel, limestone, or sandstone, through which water flows and is stored. An artesian aquifer is confined between impermeable rocks or clay which causes this positive pressure. The recharging of aquifers happens when the water table at its recharge zone is at a higher elevation than the head of the well.

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

Artesian wells were named after the former province of Artois in France, where many artesian wells were drilled by Carthusian monks from 1126.

Coordinates: 51°12′26″N 2°39′07″W / 51.2073°N 2.6519°W / 51.2073; -2.6519

Wells is a cathedral city and civil parish in the Mendip district of Somerset, England, on the southern edge of the Mendip Hills. Although the population recorded in the 2001 census is 10,406, it has had city status since 1205. It is the second smallest English city in terms of area and population after the City of London although, unlike the latter, Wells is not part of a larger metropolitan conurbation, and is consequently described in some sources as being England's smallest city.

The name Wells derives from the three wells dedicated to Saint Andrew, one in the market place and two within the grounds of the Bishop's Palace and cathedral. There was a small Roman settlement around the wells, but its importance grew under the Saxons when King Ine of Wessex founded a minster church in 704, around which the settlement grew. Wells became a trading centre and involved in cloth making before its involvement in both the English Civil War and the Monmouth Rebellion during the 17th century. In the 19th century, transport infrastructure improved with stations on three different railway lines.