A well that flows at the surface without pumping, because it is sunk into a confined aquifer with a hydraulic head (sometimes called the potentiometric or piezometric head) that lies above ground level. The aquifer is confined between two layers of impermeable rock or clay that are depressed, forming a basin. The water table lies below the ground surface at the top of the basin, but lower down the slope water draining downward by gravity is held under pressure. When a well is sunk into the aquifer water rises potentially to the level of the water table (see the diagram). See artesian water.
Subjects: Ecology and Conservation.