Tap water can be used but even treated is just going to lead to problems that will end up costing more down the road. Water from stores will cost money and eventually lead to frustration and PWC
's becoming more of a chore than they are because of the trip to the store, buying, carrying, mixing, etc. You can get a small ro
unit that will give you the ideal situation from the start and get you started in the right direction. In fact one of the members here did a comparison and it pays for itself in short order. Ultimately it is up to you. But the first option will have you frustrated for sure.