That has been our experience, brewing with the local water supply, with little or no treatment. The beers have ranged from good to very good.
Adding a few grams of this and that did seem to make a difference, but it's impossible to know for sure.
But the last German Pils we brewed and put in the keg a week ago using treated water, has all of us excited. It will be entered in a contest the end of this month.