Tap Water here. Add a little chor-out to remove the chlorine and chloraimnes. Mix up some IO let it mix a few hours roll with that. Tap water here is very good quality, and I do test it from time to time to be sure it is still good. Run the basic Cl, Cu, NO3, NH4, Si, and PO4 and we get free water reprots on our tap water form the EPA for any other items i cant test for that i am cuirous about. Now i use my RO/DI unit for makimng coffee, water for the Iron and washing windows and in My car radiator.