I'm a tap water drinker myself, but only after moving away from a city where water from other areas had to be imported to reach safe levels (according to EU regulations) because several garbage deposits of thousands of tons leaked for decades unhindered:
One might imagine that diluting such water to reach "safe" levels is not as healthy as water that never saw a toxic waste dump.
It's also not the case that tap water is always safe, even if it's declared to be. During hot summers, there's very often bacterial contamination, requiring addition of chlorine or other antiseptics. But until that is caught, some days might go by.
Sorry, the phrasing might not have been clear. Until that event, I was always propagating to drink tap water. After that I realized that research is important.