<P> The water table should not be confused with the water level in a deeper well . If a deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in this aquifer may rise to a level that is greater or less than the elevation of the actual water table . The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface, not the water table . </P> <P> The water table may vary due to seasonal changes such as precipitation and evapotranspiration . In undeveloped regions with permeable soils that receive sufficient amounts of precipitation, the water table typically slopes toward rivers that act to drain the groundwater away and release the pressure in the aquifer . Springs, rivers, lakes and oases occur when the water table reaches the surface . Springs commonly form on hillsides, where the Earth's slanting surface may "intersect" with the water table . Groundwater entering rivers and lakes accounts for the base - flow water levels in water bodies . </P> <P> Within an aquifer, the water table is rarely horizontal, but reflects the surface relief due to the capillary effect (capillary fringe) in soils, sediments and other porous media . In the aquifer, groundwater flows from points of higher pressure to points of lower pressure, and the direction of groundwater flow typically has both a horizontal and a vertical component . The slope of the water table is known as the hydraulic gradient, which depends on the rate at which water is added to and removed from the aquifer and the permeability of the material . The water table does not always mimic the topography due to variations in the underlying geological structure (e.g., folded, faulted, fractured bedrock) </P> <P> A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone . This occurs when there is an impermeable layer of rock or sediment (aquiclude) or relatively impermeable layer (aquitard) above the main water table / aquifer but below the surface of the land . If a perched aquifer's flow intersects the Earth's dry surface, at a valley wall, for example, the water is discharged as a spring . </P>

Diagram to show how surface water reaches the watertable to become groundwater