If I travel to the US (Let's say Los Angeles, Seattle and New York) how do I know if the tap water is safe to drink? In the EU I normally just ask a local. In Germany it's safe to drink but in the Czech Republic you might be better off drinking bottled water (last time I checked was ~10 years ago, sorry if it's changed).
With the recent worries about BPA and other components of plastics, it's unclear if bottled water from plastic is safer than tap at the 99.9th percentile of paranoia. I don't know about exotic risks from bottled water in glass (radioactive Evian from Chernobyl?), but I assume they are there also.
Nonetheless, in my circle of friends, I do know people who drink bottled water because they think it's more pure. I also know people who don't use microwave ovens because of harmful radio waves, and others who do not use plastic containers or plastic-lined metal cans because of hormone disruptors in plastics. I think they're nuts, and they compensate by thinking I'm naive and complacent.