Well performance is influenced by several factors, including the nature of the ground from which the ground water is being extracted, the nature of the well screen used in the well (if any), the diameter of the well, the pumping rate, etc. We often think of a well as having unlimited capacity, and in relative terms, there are some wells that approach this performance. In reality, though, all wells have a finite production capacity, and this capability can be measured a number of ways. Among the most accurate ways to measure well production is the pump test; pumping water out of the well, at varying flow rates, and measuring how the water level in the well is affected over time. Figure 1 shows a drawdown chart created from such a test.
Besides offering an accurate way to determine well performance, pumping is a good way to develop a well. By pumping at increasing flow rates, over a period of several hours, to a rate slightly faster than the pumping requirement of the job, foreign matter left in the formation and filter pack around the well screen from the drilling operation is removed, so the well will produce good clear water. In Figure 1, the operator's notes about water quality in the right column show the well clearing during the pump test.