Replacing a car water pump involves draining the car's cooling system, accessing and removing the old pump from the engine, preparing the engine block for the new pump and fitting a replacement pump in the place of the old one. You need a replacement pump that suits your car's model and engine size.
Before draining the cooling system, ensure that the car's engine is cool, and detach the battery connection from the engine to avoid a possible electric shock. Empty the coolant into a drain pan until no coolant comes out of the system. Accessing the pump involves removing engine parts such as the pulley and drive belts out of the way. Once you access the pump, remove all hoses connected to it, loosen off the bolts that secure the pump in place, dislodge it out of place, and set it aside. Remove the pump's gaskets, and set them aside as well.
To prepare the engine for the new pump, wet a cloth with a liquid engine cleaner, and wipe the engine block with the cloth, including the section previously occupied by the old pump. Be sure to remove all dirt, debris and dust from the engine block before reinserting the gaskets. Then, fit in the replacement pump, and secure it in place with bolts, taking care to apply the recommended torque to the bolts. Reassemble all the detached parts of the engine, and fill the cooling system to complete the process.