Water must migrate through the pore spaces of rock. Underground water moves under a hydraulic gradient - a slope to the water table. Hydraulic head - the difference in height of the water table between the recharge and discharge points. Springs Occur where the water table intersects the earth's surface. Water in hot springs and geysers moves up from greater depths where it has been heated by the natural geothermal gradient, or by cooling igneous bodies.
Water expands when it is heated.
Common wells Where water is artificially withdrawn from the earth. Result in drawdown of the water table - a conical depression in the water table known as a cone of depression. Cone of depression increases the hydraulic gradient in the vicinity of the well. Where the hydraulic gradient causes the water in a well to move to a level above the aquifer. Aquitards must be present both above and below the aquifer to keep the water from escaping.