I have used tap water that i leave out for 24 hours so the clorine evaporates. Never had any problems
I had a 20g Reef tank w/ hard and soft corals, inverts and fish for 2+years (untill i moved)
now i have a 45 fowlr
it really depends on your local water supply.
mine is fine, so make your own call...
-Oozy-