The water pump on your engine is a classic example of "if it ain't broke, don't fix it." It pressurizes and drives coolant through the engine's water jackets and intake manifold and circulates it through the radiator, where it disperses its heat to the outside air through the radiator's coils and fins.
Usually the water pump lasts for the entire life cycle of a vehicle, but water pump failure does happen—sometimes it's a defective pump or a poor design, but more often than not it's due to poor cooling system maintenance.
Coolant (a 50/50 mix of distilled water and glycol antifreeze) contains anti-corrosion agents, lubricants, and other additives that keep the water pump, radiator, and thermostat in good shape and prevent cavitation, gasket leaks, and other problems. That's why it's important to stick to manufacturers' recommendations for maintenance on the cooling system (and be sure to use the right coolant, since there are several varieties on the market now).
Signs of water pump failure can include poor cooling system performance, coolant leaks, overheating, and a rattling sound from worn bearings in the pump.
Let's let Dr. Coolant (John Force) weigh in on water pump failure.