What Do We Mean by a Water Table?
Not far below the surface of the land there is a zone where the soil is saturated (filled) with water. The topmost level of this saturated zone is called the water table. A water table describes the boundary between water-saturated ground and unsaturated ground. Below the water table, rocks and soil are full of water. Pockets of water existing below the water table are called aquifers.
This underground water comes mainly from rain and melted snow that soaks into the ground. Irrigation from crops and other plants may also contribute to a rising water table. This seeping process is called saturation. As the water trickles downward, the layers of sand and rock below become completely soaked with water.
An area’s water table can fluctuate as water seeps downward from the surface. Underground water is usually pure and cool and is one of the best sources of water for man’s use. Many cities add to their water supply by drilling wells below the water table and pumping up the water.
The water table sits on top of what experts call the zone of saturation, or phreatic zone. The area above the water table is called the vadose zone. Unlike the tables you’d find in your house, a water table usually isn’t flat, or horizontal. Water tables often (but not always) follow the topography, or upward and downward tilts, of the land above them.
Sometimes, a water table runs intersects with the land surface. A spring or an oasis might be the water table intersecting with the surface. A canyon, cliff, or sloping hillside may expose an underground river or lake sitting at the area’s water table. In addition to topography, water tables are influenced by many factors, including geology, weather, ground cover, and land use.