I moved down to CA and everyone uses tap water I think they are crazy, they say it is safe but when I tested it I found over 5.0 and nitrates around 20 I told both stores they were crazy and haven't been back since. I don't support those kinds of stores, they only want to make a buck, I have been sharing my knowledge about R.O/D.I with a few people down here they only listen after they see my tank. I have made really bad mistakes when I first started, I used tap, didn't see anything wrong with it until I put corals in and a few days later started to melt, phosphates were way to high and it was a pain in the butt getting it stable. Lots of money went into chemical additives which I didn't need if I were to use R.O might seem like a wast but think of your livestock. Many stores in WA supply R.O or D.I if you don't like wasting your water let them. I am getting my water from Safeway or Winco, for top offs and make my own for water changes, this might make it easier for you to.