When I lived in town and had public water, I started a 20 gal tank. I had no idea what ro/di was, so I went to Walmart and bought 20 1-gallon bottles of distilled water (NOT spring) and started my tank.Tazawa tank said that you can use tap water for mixing saltwater if you start out with live rock and live sand to start for first saltwater tank and he’s said that reef tank need RO/DI water
A BUNCH of people have told you it's a bad idea, but go ahead and listen to 1 guy who agrees with you. You'll only do it once...