Groundwater

Groundwater is water in the saturated zone of earth materials under pressure greater than atmospheric, i.e. positive pressure. Remember that in the soil profile water is held at a negative pressure due to the attraction between negatively charged clay particles and water. The groundwater table is the depth at which the pressure between water and the surrounding soil matrix is equal to atmospheric pressure. Water enters groundwater storage primarily by infiltration/percolation, although recharge by seepage from surface water bodies may occur. Water leaves groundwater storage primarily by discharge into rivers or lakes, but it is also possible for water to move upward from the water table into the capillary fringe, a zone above the groundwater table that is saturated.