The most reliable way to measure the depth of a water table is to measure the water level within a shallow well using a measuring tape. Surface geophysical methods are occasionally used when no wells are available. These methods utilize electric or acoustic probes to determine the level of the water table. State governments typically maintain a database of drilling records that provide information on past measurements and water table measurements.
Water table depths and measurements may vary depending on the time of year. Snow melts during late winter and spring typically cause a significant rise in the water table. Heavy rains or melting snow accumulations can release large quantities of water over a very short time, which infiltrates into the ground and causes the water table to rise. Water tables lower during hot dry summers due to the growth of water-loving plants and reduced rainfall totals.
The presence of underground aquifers may also influence water table measurements. Ground water that infiltrates through pore space within the soil may pass into an aquifer and lower the surrounding water table. The water table is often confused with groundwater levels in a deeper wells, where water levels are determined more due to the pressure from aquifers rather than atmospheric surface pressure.