In an artesian aquifer system, the weight of the water from the upper part of the aquifer exerts pressure in the lower part of the system, which contains the artesian well, the only opening through which water can escape. This forces the water to rise in the well.
In an artesian aquifer system, water rises in the well under its own pressure. If the pressure is high enough, the water rises to the surface and flows freely. The water from these systems can be pure or strongly mineralized.
The artesian well is either manually drilled or naturally occurs in the aquifer, which is a water-bearing layer of porous rock. The aquifer lies between two impervious layers of rock. The artesian system, which includes the aquifer and the impervious layers, slopes downward, and the well is sunk at a point lower than the place where water, from rain or melting snow, enters the system. The weight of the water from the upper portion of the aquifer forces the water to rise in the well. If there is a natural opening in the impervious layer above the aquifer, the forces at work thrust the water to the surface. At the surface, the water flows freely, forming an artesian spring.
The name "artesian" is derived from a place called "Artois" in France. In Artois, such wells were sunk as early as 1126.