I've yet to visit a country that didn't sell bottled water though. That doesn't seem US specific

Many other countries have tap water that is not potable.

As do some places in the U.S. and many people do fear that their water while technically potable, is full of unhealthy materials like lead. Even for me in a relatively new building, I have no idea about the materials of the lines built into it or the water main in my city. I use a Brita or straight from the tap personally but I can't say I blame people who are concerned (in the U.S.) where infrastructure is quite old and there doesn't seem to be much concern by officials even in the most dire of cases like Flint to fix things.