The term “water table” implies to most people that it has something to do with groundwater, as it can be defined as the upper limit/surface of abundant groundwater (subsurface water). The water table is one of the many types subsurface water.
What is Subsurface Water?
Subsurface water is the water which lies beneath the ground surface or lithosphere. There are many types of subsurface water types and they are categorised into to main groups: Unsaturated Zone and the Saturated Zone (Phreatic Zone).
Within the top later of soil there are pore spaces which are tiny holes in sediments or bedrock. These pore maybe completely filled with water, air or contain a combination of both. This zone is affected directly by heavy rainfall becoming almost saturated with water and by long dry spells becoming almost dry.
It is mainly through rainfall that the unsaturated zone collects water. As precipitation infiltrates downwards through the unsaturated zone it is collected in the pores in the ground. The infiltrating water is known as soil water and is at a depth of 6-10 feet. Further beneath the soil water lays the vadose water, which is below plant roots by still within the unsaturated zone of water and air. As infiltration continues to occur, the excess water will reach the water table.
This area of the ground all the pore spaces and cracks in the sediments and rocks are completely filled with water, hence being saturated. Thus all water found at this level is groundwater.
The water table is the upper limit of the groundwater and also varies in depth, rising when being recharged and decreasing when the groundwater is discharging. The water table is generally deeper beneath hills and shallower beneath valleys. The water table is also affected by weather, whereby seasonal rains and droughts can lead to an increase and decrease in the height of the water table respectively. It should also be noted that excessive pumping of groundwater can lead to a decrease in the water table level.