Adding water to the car water tank can indeed be used to cool the engine, but the water in life is impure and contains impurities, which will cause the cylinder to be pulled, the cylinder head deformed, and more seriously, the engine will be scrapped.
Water is also a kind of coolant, and it can also cool the car radiator engine. The coolant filled in the engine is also mixed with the original coolant and water according to a certain standard ratio.
In a compromise, if your car really lacks coolant for some reason, you can temporarily replace it with distilled water. The harm of using water instead of antifreeze coolant.