I don't use distilled, I'v thought about it, but never have, if it makes you feel better, get a big pot or a pressure cooker from a thrift shop, and boil up some tap water to make distilled, let it boil say, 10 min, then it's ready for the car. replace all rubber coolant lines and flush cooling system entirely b4 putting distilled water in, if not the remaining minerals will mix with the distilled water and it will be tap water again.