Groundwater that is confined in an aquifer, but which may overflow on to the land surface via artificial boreholes or, sometimes, natural springs, because of the high hydraulic head that may be developed in a confined aquifer. Artesian conditions are common when the aquifer has a syncline form. The London Basin, England, provided artesian water during the 19th century from a chalk aquifer sealed by clays. The term is derived from the Artois region of north-western France.