I used to buy bottled water pretty often. I didn't like the taste of our tap water, and I didn't want to buy soda or juice at school/gas stations/wherever.
Then I realized how much I was spending. Not only that, but the number of plastic water bottles that end up in landfills instead of being recycled was disgusting (to me, anyway.)
Soooo...I bought a Brita pitcher. It's absolutely wonderful, and like lasereth said, it makes the yucky tapwater taste like awesome (well, I'm paraphrasing a bit
) Then I bought a hard plastic water bottle that I carry with me all the time. I save money, I don't have to go on a scavenger hunt for a recycling bin, and I get cold, yummy water. Everybody wins. (and by everybody, I mean me.)