Water pumps come in many designs, but most comprise a revolving impeller, which forces the coolant during the engine block. In most rear wheel drive cars, the fan is installed on the end of the water drive shaft.

Many water pumps have a spring-loaded seal to avoid outflow of water around the pump shaft. Modern pumps are fixed with pre-packed ball bearings, which are preserved at each end to abolish the need for lubrication. Impeller type water pumps must turn fast to be efficient, and worn or loose drive belts can permit slippage which is not simply detected.