What is a water table?

SAN DIEGO COUNTY - Many people understand that a water table has something to do with ground water, but they may not understand fully what a water table entails or the purpose it serves.

The zone of saturation is the underground depth at which the ground is totally saturated with water. The upper surface of this zone is called the water table. It is also the level at which groundwater pressure is equal to atmospheric pressure.

Much of the water present on Earth is trapped under the ground. Rain, river and stream runoff and snow melt contribute to the water that seeps down into the soil and eventually into deposits of water under the ground. When water deposits are large enough to be used as a water source, they are known as aquifers.

The water table can fluctuate depending on the season and weather conditions. When there is an excess of rain or runoff, the water table may rise considerably. During periods of drought, the water table may diminish.

It’s also important to note that a water table is not a flat line of water. The table actually fluctuates depending on the landscape and human modification of subterranean topography. The water table may be shallow in some areas and deep in others. In some cases, people may live in areas with a “high water table.”

The water may be enough to saturate the ground and contribute to springs where water flows naturally from rock onto the surface of the land. Springs may seep from places where the water table intersects the land surface. Water may also flow out of the ground along fractures.

A high water table may contribute to leaks in basements and crawl spaces. That’s because hydrostatic pressure, or the pressure of the groundwater pressing up against the home foundation, can cause the water to find weak points and other areas of entry. In these instances, a method of keeping the water from entering the home may need to be investigated.

Some people and industries tap the water table and aquifers for use. Underground water can provide irrigation for crops or be used to bring water to a home instead of relying on public water supplies. When a well is sunk to pump ground water, it must be put deep enough to reach the zone of saturation.