Good point .you are correct to think that. In any water system of the water is not balanced chemically it may start trying to balance itself out by taking from the environment. In this case the environment would be parts in the coolant system. The water can leach from the plumbing for example. This happens alot in swimming pools. Three way to ensure this doesn't happen is we use this equation called the Langlier equation. If its too corrosive we add more base... corrosiveness is what eats up the pipes.. If its too alkaline we add more acid. High alkalinity starts to scale the pipes and equipment. For coolant prob not a good idea to add a layer of scale in the radiator and engine block
