Artesian

Artesian is a term used in geology and hydrogeology to describe water and wells associated with a confined aquifer under pressure. In an artesian setting, groundwater is trapped between impermeable layers, so the water in the aquifer is under hydrostatic pressure rather than simply sitting at atmospheric pressure. When a well is drilled to reach this aquifer, the internal pressure can cause the water to rise up the borehole, and in some cases to flow freely at the surface without pumping.

The mechanism behind artesian systems relies on recharge in a higher-elevation area relative to the well, with the aquifer extending between permeable and impermeable boundaries. The water level inside a properly constructed artesian well reflects the piezometric surface—the level to which groundwater would rise within a borehole due to the pressure in the confined aquifer. If the hydraulic head is high enough, the well becomes flowing, delivering water at the surface without mechanical aid.

Etymology traces the term to the French artesien, ultimately associated with the region of Artois in northern France, where early observations of pressurized wells led to the name. Artesian conditions are found worldwide, from sedimentary basins to large aquifer systems.

One notable example is the Great Artesian Basin of Australia, one of the largest and most important groundwater systems. Artesian waters have historically supplied public and agricultural water supplies and remain a focus of groundwater management and sustainability efforts. Modern concerns emphasize maintaining recharge areas, preventing over-extraction, and monitoring groundwater quality in artesian aquifers.