It all depends on what you want to do with the water, what your source water is, and where the bottled water actually comes from.
MOST bottled water is just filtered municipal water, and most "spring water" is just heavily filtered water (and/or maybe run through a RO/DI system with minerals added back in for taste. The water from the "water machines" in the stores is usually more than sufficient for drinking IMO. Our tap water here tastes like shit. Heavily chlorinated. While it's true that the Pur and Brita filters remove most of the chlorine and some impurities, they leave lots of the other crap that really isn't all that healthy for you: Nitrates, phosphates, organic and inorganic chemical pollution, etc.
If your tap water sucks, bottled water or a good RO/DI with a post DI carbon filter is the way to go.
BTW, the EPA only sets the minimum standards for drinking water, and they're not that high. Better than most of the world? Yes, but many nasties are still permitted.