The water table and an aquifer are terms used when discussing groundwater. The major difference between the two terms is that the water table references a specific portion of groundwater and an aquifer is all the groundwater present in the area.
The Water Table
The water table is the upper most section of the saturation zone in the ground. The saturation zone is the area of ground in which water has penetrated and fills all the gaps in the ground, completely saturating it. As time progresses, the saturation zone may raise or lower depending on levels of precipitation. As the saturation zone changes, so does the water table level. For example, if the weather is dry, the water table may become deeper as less water is available. An aquifer is the water beneath the water table.
An aquifer is a body of saturated rock through which water can easily move, according to the Idaho Museum of Natural History. Water moves through the pores of the rock. The pores act as a natural filtration system, removing even viruses and bacteria from the water. Aquifers can be considered unconfined or confined. An unconfined aquifer's bottom is a layer of nonporous rock, which restricts water flow, creating a barrier to the aquifer. The water table is the top layer of the unconfined aquifer. A confined aquifer sits below a unconfined aquifer and layer of nonporous rock.
The depth to reach the water table varies from place to place. For example, the water table is typically deeper on hills than it is in valleys, according to the Ground Water Trust. In some areas, the water table may only be a few feet below the surface, or it may be hundreds of feet down. The depth of an aquifer can also vary from a few feet to hundreds of feet of available groundwater.
Wells used from pumping groundwater to the surface must be drilled below the existing water table line and into the aquifer. The water can flow into the well and pressure is used to pump the water to the surface. Wells can draw down the water table by removing more water than is replaced back into the aquifer. If the well or lack of precipitation draws the water table below the well, the well runs dry.