According to the Associated Press:
"A vast array of pharmaceuticals — including antibiotics, anti-convulsants, mood stabilizers and sex hormones — have been found in the drinking water supplies of at least 41 million Americans. The concentrations of these pharmaceuticals are tiny, far below the levels of a medical dose but the long-term consequences to human health are unknown."
The pharmaceutical industry points out the amount of medication in the water supply is the equivalent of a single pill in an Olympic-size swimming pool. Still, if you a have glass of water in Philadelphia, you are drinking tiny amounts of at least 56 medications.
CNN has a map of the affected metro areas and a video explanation of how drugs end up in tap water.
The Wikipedia article about drinking water comments on the "Tap Water vs Bottled Water" debate: "Many large corporations and some water companies are now making an effort to promote tap water over bottled water. The mayors of San Francisco, Salt Lake City and Minneapolis signed a pledge to promote tap water over bottled water as part of the “Think Outside the Bottle” campaign."
AP Probe Finds Drugs in Drinking Water. Associated Press.
Drugs in water causing troubling problems to fish, wildlife. CNN.
In U.S., bottled water lacks drug safeguards. CNN.
Faucet image source: OpenClipArt.org (public domain).