Can Water Be Added to Coolant?

[McFinn]

Coolant can have a small amount of distilled water added, but tap water should not be used as it is particularly prone to forming scale, which can easily clog pipes. Adding water to antifreeze will raise its freezing point. Normally, antifreeze has a freezing point of -25°C, but if diluted with water, the freezing point can increase by about 10°C. In such cases, driving to colder areas may cause the antifreeze to freeze, potentially damaging the radiator and water tank. An imbalance in the additive ratio of antifreeze reduces its effectiveness, making it more susceptible to scale formation and radiator corrosion. In severe cases, leakage may occur.