A water pump is a vital component of the engine's cooling system, and it circulates engine coolant/antifreeze through the engine block, radiator, and other cooling system components. The water pump should be replaced whenever it starts showing signs of wear, such as leaks, rattling, or reduced performance. Additionally, it is recommended to replace the water pump as part of regular maintenance every 60,000-100,000 miles to prevent potential failures that could cause severe engine damage.