A single unit of bottled water takes as much as 7 times as much water to produce it. Not to mention the large amount of carbon used to mine it, suck it, clean it, make the bottle, transport the bottle, put the water in the bottle, etc.
Tap water in the U.S. is excellent. If it tastes bad, use a filter like a Brita to make it taste better. Bring a reusable bottle to work, exercise, or class. The safest type of reusable plastic bottle is the same plastic as milk jugs, HDPE. Do not reuse bottled water bottles as they leach chemicals if reused.
Polycarbonate or LEXAN is suspected of mimicking female hormones and should only be used when needed, like the few times a year you camp or back pack. Washing polycarbonate by hand is best.