Hexavalent chromium, the "Erin Brockovich chemical" widely believed to be a human carcinogen, has been found in the tap water of 31 of the 35 cities tested recently by Environmental Working Group.

That is some scary news. For some context, at least 74 million people are thought to be drinking tap water polluted with "total chromium," according to EWG, yet the EPA has no established legal limit for hexavalent chromium in tap water, and does not require testing by water utilities.

Some might interpret this as reason to head straight for the bottle—that's no better, however, and I thought a recap might be useful of why, exactly, it's not. Discover some of the top reasons bottled water is still an eco-sin.