Artesian spring:

The artesian springs are formed when water bearing strata is confined between two impervious layers and water comes to the surface under pressure. In this case, water finds its way to the surface where the overlying impervious material is absent or through a fault. It breaks through at places where it is not sufficiently strong or compact to resist the upward pressure.

The yield from artesian spring is often uniform throughout the year. Where a spring of this type exists, it has been found that the ground water stream from which it is fed is of considerable size and the water of the spring is from a small portion of entire flow. In such cases, the yield is increased by enlarging the opening or by sinking wells and pumping from them as in case of ordinary ground water supply.

Figure: Artesian Spring