Actually, I'd like to point out that most major metropolitan cities in the US (Los Angeles, San Francisco, etc.) have a bit of fluoride in the water, which helps keep your teeth clean.
This is in contrast to water in parts of Europe and other asian countries and you can easily see the difference in their teeth.
http://answers.google.com/answers/threadview?id=521352
The standards for safety are stricter on tap water than bottled water.