what is the water table

The water table is the upper surface of the zone of saturation, which is where the pores and fractures of the ground are saturated with water. It is the boundary between the unsaturated zone and the saturated zone underground, and below the water table, groundwater fills any spaces between sediments and within rock. The water table is the surface where the water pressure head is equal to the atmospheric pressure, and it 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, and groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies. The depth of the water table can be measured using various methods, including drilling wells and using electrical resistivity imaging.