The concentrations are tiny, measured in quantities of parts per billion or trillion. That's far below the levels of a medical dose. Utilities insist their water is safe, but some scientists are worried about the long-term consequences to human health.
Researchers don't yet understand the exact risks from decades of exposure to combinations of low levels of pharmaceuticals. But recent studies have found alarming effects on human cells and wildlife.
In the course of a five-month inquiry, the AP discovered that drugs have been detected in the drinking water supplies of 24 major metropolitan areas. Detroit reports unspecified drugs were found.
The AP found water providers rarely disclose results of pharmaceutical screenings, unless pressed.
Of the 28 major metropolitan areas where tests were performed on drinking water supplies, only Albuquerque; Austin, Texas; and Virginia Beach, Va.; said tests were negative. The drinking water in Dallas has been tested, but officials are awaiting results. Arlington, Texas, acknowledged that traces of a pharmaceutical were detected in its drinking water but cited post-9/11 security concerns in refusing to identify the drug.
The AP also contacted 52 small water providers - one in each state, and two each in Missouri and Texas - that serve communities with populations around 25,000. All but one said their drinking water had not been screened for pharmaceuticals; officials in Emporia, Kan., refused to answer AP's questions, also citing post-9/11 issues.
Rural consumers who draw water from their own wells aren't in the clear either, experts say.
Even users of bottled water and home filtration systems don't necessarily avoid exposure. Bottlers, some of which simply repackage tap water, do not typically treat or test for pharmaceuticals, according to the industry's main trade group. The same goes for the makers of home filtration systems.