tap water in most cases doesn't seem to bother fish too bad, Its when you have invertabrates and corals that you run into problems
other problems associated with tap water are horrendous algae problems, if you use tap for a while, you'll see exactly what im talking about
although
there are many people with fish only or FOWLR tanks that use tap water sucessfully
even fome reef tanks use it but you need clean reliable source water
hope this helps and good luck on the new tank