Plastic bottles leech carcinogens into the water.  (Known fact; I learned that from Dr. David Suzuki.)  Municipal water in medium and large sized cities is heavily chlorinated.  Better than non-chlorinated in terms of disease prevention - but still not healthy in the longer term.

The only people who have really safe water are people in smaller cities and towns using a municipal water supply OR those who have their own wells - all of which must be tested regularly to ensure safety.