The water table is the underground depth at which point the ground is totally saturated with water. Much of the Earth's potable water is actually locked up underground, and while it may not be as physically obvious as big lakes and rivers, it is critically important. When underground water deposits are large enough to be considered sustainable for use, they are known as aquifers. The water table could also be thought of as the top of the aquifer.

A number of things contribute to the formation of the water table. Every time it rains, for example, water trickles into the water table. Runoff from lakes, rivers, and streams also contributes, as does snow melt. It is also necessary for the rock in the water table to be permeable, meaning that it can be saturated with water. Impermeable rock cannot collect water, although aquifers are often surrounded by deposits of impermeable rock which keep the water trapped inside.

The level of a water table can fluctuate considerably. A dry spell, for example, can cause the water level to drop, and in some reasons, the seasonal fluctuation of the water table is common enough to be expected. Excessive use of water can also deplete the water table, as for instance when a population increases suddenly, demanding more water than was used previously. Water table depletion is especially common in areas where water is used in industrial production.

To access the water table, people must often dig wells which penetrate the ground until they reach the water table. Digging a well is a science, as the well must be situated in a location where the water table is close to the surface, and in an area where underground deposits are present. When a well is sunk through impermeable rock to reach the water table, it is known as an artesian well. It is also possible to access the water table through springs which bubble up at the Earth's surface.

From the name, you might think that the water table is a flat line which neatly divides various regions underground. This is not the case. The water table usually fluctuates with the landscape, ebbing close to the surface in some places and diving deep below in other instances. The shape of the water table can also be determined by the surrounding rock, and by human activity. For example, when humans deplete an aquifer, they may trigger collapses of rock and soil, deforming the shape of the water table.