Bottled water has three general problems -- it's wasteful, expensive, and unsanitary.
a) They are horrible for the environment (17 million barrels of oil are used in the production of water bottles every year).
b) It takes 3 times the amount of water to produce the bottle as it does to fill it.
c) Bottled water is extremely costly relative to tap water (up to 10,000x as expensive) -- .0015 cents / gallon vs $10 / gallon). In some alternate universe, this might actually be worth it if the water was sanitary, but it's not (points d, e, and f).
d) 40% of bottled water has been taken from municipal water sources (i.e. 40% of bottled water IS tap water).
e) 22% of bottled water contains chemical contaminants at levels above strict state health limits.
f) Bottled water isn't regulated like tap water is. It doesn't have to be checked for E Coli, it is not subject to quality reports, the companies that produce it are not required to provide the source of the water, and it can still be distributed when tap water standards (which are deplorable and outdated it and of themselves) are not met.
Basically, bottled water is even worse than tap water, on almost every count. Except, I think it tastes better, (but certainly not because it's cleaner)