American tap water has been getting worse over the years and Fatbat is totally right bout the larger cities being worse than small towns. Lived in Chicago, Detroit, Philly and Fort Worth and also in a bunch of little towns; city water sucks.
Ironically here in Mexico I have a little ranch with a well and that is the cleanest damn water I've found. We had it tested when we bought the property and it's safe to drink. Of course we still filter it but it's bad ass, just clean pure water, ice cold all year round. Here at my city house though we don't even use the tap water to brush our teeth. Everyone buys water, trucks pass a few times a day to pick up your empty 5 gallon bottles and sell you full ones.