The US has pretty good tap water in most places. Of course there are outliers we are talking about a giant country.

While you are right to trust most tap water in Europe we also have a lot of outliers. Old plumbing being probably the biggest problem. But also the taste can be atrocious. The worst tasting tap water I ever needed to drink was in Barcelona.

Edit: and the worst looking tap water I ever saw was in Paris. (It was old pipes or something as it was brown, almost red)