...bottled water sold in the United States is not necessarily cleaner or safer than most tap water, according to a four-year scientific study recently made public by NRDC.

NRDC's study included testing of more than 1,000 bottles of 103 brands of bottled water. While most of the tested waters were found to be of high quality, some brands were contaminated: about one-third of the waters tested contained levels of contamination -- including synthetic organic chemicals, bacteria, and arsenic -- in at least one sample that exceeded allowable limits under either state or bottled water industry standards or guidelines.

(Later in the article, it goes on to say In fact, about one-fourth of bottled water is actually bottled tap water, according to government and industry estimates (some estimates go as high as 40 percent). And FDA rules allow bottlers to call their product "spring water" even though it may be brought to the surface using a pumped well, and it may be treated with chemicals.

more, see: http://www.nrdc.org/water/drinking/nbw.asp