RE:RE:good luckDiesel drivers regularly add DEF fluid to an auxiliary tank which is required by modern diesel engines for low emissions. I don't think the addition of distilled water is going to be that much of a problem. Besides, almost every supermarket carries distilled water. It is not hard to find. Eventually, Truck stops will stock distilled water if this unit becomes popular. The video mentioned that there is an indicator light that shows when the tank is almost empty.