Aquifer water level
When a well is placed so that its screen or open end is within an aquifer, water will rise inside the casing to a level that represents the aquifer's "potential energy head." In a water table well, this level would coincide with the top of the surface saturated zone or the "water table." In confined wells such as buried artesian or bedrock situations, where the aquifer water is under pressure, the level in the casing will be above the top of the aquifer.
A record of measurements, gathered over time, of the depths to water in the well is illustrated by a hydrograph and provides information about the relative quantity of water at different times. A long-term record indicates how the aquifer responds to climatic conditions and ground water withdrawals.