I don't remember the source, but I recall reading that, paradoxically, tap water in cities is much better quality than bottled water, due to stricter controls. Probably doesn't taste as good, but you can be quite sure it won't harm you.
The tap water from the small village in the Italian country I was born in is the best I've ever had, but I drink straight from the tap in London without any issues, except when I need to satisfy my craving for sparkling water.
