To be sure, the concentrations of these pharmaceuticals are tiny, measured in quantities of parts per billion or trillion, far below the levels of a medical dose. Also, utilities insist their water is safe.
But the presence of so many prescription drugs - and over-the-counter medicines like acetaminophen and ibuprofen - in so much of our drinking water is heightening worries among scientists of long-term consequences to human health.
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 - from Southern California to Northern New Jersey, from Detroit to Louisville, Ky.
Water providers rarely disclose results of pharmaceutical screenings, unless pressed, the AP found. For example, the head of a group representing major California suppliers said the public "doesn't know how to interpret the information" and might be unduly alarmed.
How do the drugs get into the water?
CBS News correspondent Nancy Cordes reports that, according to the AP study, it's the fault of every American who ever took a pill.
When people take medicine some gets absorbed by the body, but the leftovers end up getting flushed down the toilet and into the water supply.
Some of the water is cleansed again at drinking water treatment plants and piped to consumers. But most treatments do not remove all drug residue.
Treatment facilities aren't required to test for pharmaceuticals or filter them out, reports Cordes.
And while researchers do not yet understand the exact risks from decades of persistent exposure to random combinations of low levels of pharmaceuticals, recent studies - which have gone virtually unnoticed by the general public - have found alarming effects on human cells and wildlife.
"We recognize it is a growing concern and we're taking it very seriously," said Benjamin H. Grumbles, assistant administrator for water at the U.S. Environmental Protection Agency.
Dr. David Carpenter, director of the Institute for Health and the Environment at the State University of New York at Albany, tells CBS' The Early Show that it is important to remember, "you have to drink water. And bottled water isn't any better than tap water."
Carpenter said most tap water is not treated in a way that can get out pharmaceuticals, but he said activated charcol filters - whether used at home or by water treatment authorities - do remove most chemical compounds. He said a small number of public water providers use charcol filters already.
Members of the AP National Investigative Team reviewed hundreds of scientific reports, analyzed federal drinking water databases, visited environmental study sites and treatment plants and interviewed more than 230 officials, academics and scientists. They also surveyed the nation's 50 largest cities and a dozen other major water providers, as well as smaller community water providers in all 50 states.
Here are some of the key test results obtained by the AP:
The situation is undoubtedly worse than suggested by the positive test results in the major population centers documented by the AP.
The federal government doesn't require any testing and hasn't set safety limits for drugs in water. Of the 62 major water providers contacted, the drinking water for only 28 was tested. Among the 34 that haven't: Houston, Chicago, Miami, Baltimore, Phoenix, Boston and New York City's Department of Environmental Protection, which delivers water to 9 million people.
Some providers screen only for one or two pharmaceuticals, leaving open the possibility that others are present.
The AP's investigation also indicates that watersheds, the natural sources of most of the nation's water supply, also are contaminated. Tests were conducted in the watersheds of 35 of the 62 major providers surveyed by the AP, and pharmaceuticals were detected in 28.
Yet officials in six of those 28 metropolitan areas said they did not go on to test their drinking water - Fairfax, Va.; Montgomery County in Maryland; Omaha, Neb.; Oklahoma City; Santa Clara, Calif., and New York City.
The New York state health department and the USGS tested the source of the city's water, upstate. They found trace concentrations of heart medicine, infection fighters, estrogen, anti-convulsants, a mood stabilizer and a tranquilizer.
City water officials declined repeated requests for an interview. In a statement, they insisted that "New York City's drinking water continues to meet all federal and state regulations regarding drinking water quality in the watershed and the distribution system" - regulations that do not address trace pharmaceuticals.
In several cases, officials at municipal or regional water providers told the AP that pharmaceuticals had not been detected, but the AP obtained the results of tests conducted by independent researchers that showed otherwise. For example, water department officials in New Orleans said their water had not been tested for pharmaceuticals, but a Tulane University researcher and his students have published a study that found the pain reliever naproxen, the sex hormone estrone and the anti-cholesterol drug byproduct clofibric acid in treated drinking water.
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.
The Stroud Water Research Center, in Avondale, Pa., has measured water samples from New York City's upstate watershed for caffeine, a common contaminant that scientists often look for as a possible signal for the presence of other pharmaceuticals. Though more caffeine was detected at suburban sites, researcher Anthony Aufdenkampe was struck by the relatively high levels even in less populated areas.
He suspects it escapes from failed septic tanks, maybe with other drugs. "Septic systems are essentially small treatment plants that are essentially unmanaged and therefore tend to fail," Aufdenkampe said.
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.