The problem with bottled water is that many of their claims are unsubstantiated. Regulation is very poor, and much of this "mountain spring water" is actually filtered tap water, so you're paying $1 or more for what you could have gotten at home for pennies. Tap water is regulated by the EPA, while bottled water is regulated by the Food and Drug Administration. The EPA is stricter, better staffed, and tests the water much, much more often.

http://www.nytimes.com/gwire/2009/07/09/09greenwire-fewer-regulations-for-bottled-water-than-tap-g-33331.html

My mom is a dental hygienist and she says she can always spot bottled water drinkers right away because their teeth are softer. Many cities add a small amount of fluoride to our tap water, which increases oral health (and therefore overall health).

Finally, bottled water is creating massive, massive amounts of plastic waste. Very few empty bottles actually make it all the way to recycling, and the waste is just disgusting. Personally, I think if it's bad for the planet, it's bad for individual health as well. There is literally a swirling mass of plastic the size of Texas in the ocean.

http://www.franklygreen.com/my_weblog/2008/01/video-plastic-f.html

Quite honestly, I think the bottled water fad is about vanity. There is a great episode of Penn and Teller's "Bull S**T" (the show is on DVD now) about bottled water where they told people they were drinking all of these fancy brands, recorded their comments ("this one is more mineral tasting," "ooh, you can really tell it's from the rain forest!") and then let them know it was all hose water. They all claimed to be able to taste these subtle differences because they simply wanted to think that they could.

Buy yourself a reusable water bottle, fill it with tap water, and save yourself the money. If you want flavoring, add some lemon juice or whatever at home. You're being taken for a ride by some clever marketing people and it's not worth it.