The only water I buy is the 1 Gallon of Crystal Geyser with a handle, it's easy to take around plus it helps make sure I take in around a gallon a day. It's only one dollar so not it's not a huge waste of money.
It's more convenient than lapping from puddles or drinking from a men's room faucet. I don't see too many taps when I am walking around the city on a hot day.
There are no health guidelines to follow regarding bottled water. At least not here in Canada. We have been told that the odds are, our tap water is cleaner than the bottled water people purchase from the store. Go figure.
I used to always drink from the tap, but the water in Atlanta has gotten pretty shitty, especially in my part of town. Giarardia was found a couple of times this summer.
So I don't mind shelling out $ for cheap distilled H20.