To help understand how a swimming pool functions, one should consider how the human body works. The heart circulates blood in the body much the same way that a centrifugal pump recirculates swimming pool water. The kidneys remove toxic wastes from the blood just as filters remove debris from the pool water. Just as the veins and arteries carry blood to and from the heart, so do a series of influent and effluent pool pipes.

 

Tom Griffiths, The Complete Swimming Pool Reference, second edition