Knowing how a well pump and the well in which it is installed function together is essential to proper operation of water well supplies. The horizontal centrifugal pump and the submersible pump are discussed. Also of importance is an understanding of well construction and its two main elements, the part of the well that serves as housing for the pumping equipment and as a vertical pipe through which water flows upward from the aquifer to the point where it enters the pump itself, and the intake portion of the well. Well system failures are briefly discussed, and monitoring well performance and anticipating problems with wells and pumps are also mentioned.