The Environmental Working Group tested 10 major bottled-water brands. Thirty-eight low-level contaminants turned up in the water, with each brand containing an average of eight chemicals. Disinfection products, caffeine, Tylenol, nitrate, industrial chemicals, arsenic and bacteria were all detected.
Two brands contained disinfection byproducts at levels that exceeded California's bottled-water standards, and bottles of Wal-Mart's Sam's Choice bought in the Bay Area contained trihalomethanes, which have been linked to cancer and miscarriages.
In fact, the Wal-Mart water and a brand sold on the East Coast by the Giant supermarket chain were “chemically indistinguishable from tap water.”
ABC News October 15, 2008