actually distilled water is used to top-up battery and so it is usually called battery waterhowever, in other thread, some prefer to use distilled water to also top up the radiator in the belief that it will not cause rustingfyi, I had not topped up the water for the radiator/reservoir for almost 4 years for my previous car as the level had been near max for long time
It's a Sunnymaybe, I am lucky - no leakage ........
tap water is just water with some mineralsrust formation (oxidation) occurs when you have metals, water and oxygen presentcoolant (the green stuff) usually contain rust inhibitorsso it is okay to use clean tap water instead of distilled water unless you "tong poh" your car .......
Dont anyhow mix lah, now no leakage is good, dont mix here & there, later your radiator pik jar, susa lah~Btw, got confused, the thread topic from battery water to coolant liao. haha