If you're going for a reef, it's best to use at least r/o water. I've used both that and tap water, and I can tell you, the fish respond better for sure, and algae grows much more to my liking. I now use r/o d/i bottled water from the grocery store, getting four five-gallon bottles at a time.
What is your water quality like where you live? Mine here is world-class, and still.