A water pump is installed in a vehicle to ensure that the engine can run cooly on a sunny day, as the engine already heats up when it's working; added sun will just add to the temperature. As you might know that coolants are used to cool down the engine, which are supplied by the radiator, using a water pump. The coolant travels to the engine, and absorbs all the heat as it cools the engine down. The coolant then travels back to the radiator where it cools down again, and start the process all over again. The entire process is needed to keep the engine from overheating, and is dependent on the coolant being delivered. The delivery process of this coolant is dependent on the water pump, which is responsible to delivering the coolant to the engine, and then back to the radiator to cool down. This is a cycle that keeps going around, when the vehicle is running. When the water pumps is working efficiently and effectively, it will keep on providing the vehicle with the coolant is required to prevent engine failure. The water pump inside the engine does not deliver water, but helps deliver the coolant around the engine.