If you buy bottled water, read this

First, the NRDC: Bottled Water - Executive Summary and the full report here based on a four-year study.

You might find this disturbing:
"Some of this marketing is misleading, implying the water comes from pristine sources when it does not. ...one brand of "spring water" whose label pictured a lake and mountains, actually came from a well in an industrial facility's parking lot, near a hazardous waste dump, and periodically was contaminated with industrial chemicals at levels above FDA standards.

or:
"...about one fourth of bottled water is bottled tap water (and by some accounts, as much as 40 percent is derived from tap water)..."

and a bit more
Even when bottled waters are covered by FDA's specific bottled water standards, those rules are weaker in many ways than EPA rules that apply to big city tap water. For instance, comparing those EPA regulations (for water systems which serve the majority of the U.S. population) with FDA's bottled water rules:

City tap water can have no confirmed E. coli or fecal coliform bacteria... FDA bottled water rules include no such prohibition (a certain amount of any type of coliform bacteria is allowed in bottled water).

Well, actually, just go read that executive summary -- it tells you the rest!