And forget about yogurt. Well, for the most part they didn't find any. Still, as detection methods improve, we'll eventually be able to find a single molecule of anything in Lake Superior. Already, testing is so sensitive that incredibly tiny levels of chemicals are detectable, so it's hardly surprising that the NRDC did find some chemicals in some samples, like naturally occurring arsenic, that could be harmful if ingested in massive amounts. But it makes sense to have much more stringent regulations on tap water, because that comes from a monopoly.
Municipalities have no market incentives to keep to keep their water completely safe.
Not so with incredibly competitive bottled water industry. Perrier discovered this the hard way when the FDA found traces of the benzine, a probable human carcinogen, in their bottles of mineral water nine years ago. The NRDC took more than 1,000 samples. They've located bottled-water disease outbreaks in the medical literature, they say. One in the Marianas Islands, and one in Portugal.