The topic first gained notice in Europe in the early 1990s where scientists initially found clofibric acid, a cholesterol-lowering drug, in groundwater.  In 1999-2000, the U.S. Geological Survey conducted the first nationwide investigation of the occurrence of pharmaceuticals. 80 percent of the 139-tested streams (near urban or agricultural areas) from 30 states were found to be contaminated.

According to the recent Associated Press investigation, a vast array of pharmaceuticals—including antibiotics, narcotics, steroids, anti-convulsants, mood stabilizers and birth control hormones—have been found in the drinking water supplies of at least 41 million Americans.  These Americans represent 24 of the 62 major metropolitan drinking water supplies that tested positive in this report.

- Philadelphia alone had 56 pharmaceuticals detected in its treated drinking water, including medicines for pain, infection, high cholesterol, asthma, epilepsy, mental illness and heart problems.

- New York state found trace concentrations of heart medicine, infection fighters, estrogen, anti-convulsants, a mood stabilizer and a tranquilizer.

- Anti-epileptic and anti-anxiety medications were detected in a portion of the treated drinking water for 18.5 million people in Southern California.

- A sex hormone was detected in San Francisco's drinking water.

The concentrations of these pharmaceuticals are tiny, measured in quantities of parts per billion or trillion, far below the levels of a medical dose, and many water utilities insist they are safe. Still, the study suggested that these "compounds were more prevalent and more persistent than had been thought."

While some water supplies screen their water for pharmaceuticals, most water providers typically don’t screen at all. If they do, these 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.

Possible Effects on Humans?
The pharmaceutical industry claims that levels of drugs tested are miniscule.  “The amount of medical drugs in water supply is equivalent to a single pill in an Olympic distance swimming pool.”  They also claim that there are no studies indicating any effects on human health.

But simply because there are no studies, doesn't mean there is no danger. Scientists say medications may pose a unique danger because, unlike most pollutants, they were crafted to act on the human body. "These are chemicals that are designed to have very specific effects at very low concentrations. That's what pharmaceuticals do. So when they get out to the environment, it should not be a shock to people that they have effects," says zoologist John Sumpter at Brunel University in London, who has studied trace hormones, heart medicine and other drugs.

Moreover, recent laboratory research has found that small amounts of medication have caused impeded human embryonic kidney cell growth, inflamed human blood cells and excessive proliferation of human breast cancer cells.  Scientists are increasingly wary of the lack of research in long-term, chronic and combined exposures to agents designed to cause a physiological effect in humans.  For instance, in the case of antibiotics, there is concern that long term ingestion of small doses could cause antibiotic resistance.

According to the New York Times, the FDA issued a review in 2005 admitting that the extent and consequences of human exposure to these compounds, especially in combination, are “unknown."  Meanwhile the number of new and different pharmaceuticals, the number of people taking them, and the amounts they are taking are all increasing every year.

Known Effects on Wildlife
Scientific research also indicates that the presence of pharmaceuticals in waterways has detrimental effects on aquatic wildlife. The AP describes numerous studies that found these chemicals in earthworms, fish, shrimp, oysters and other species, with troubling results. For instance, many scientists are concerned about sperm levels and spawning patterns in aquatic organisms that have been altered in environments heavily polluted with a class of hormone-altering pharmaceuticals known as endocrine disrupters. 

Whilst male fish are becoming female fish in some areas, other forms of wildlife have also been affected, and scientists have observed a wide-range of symptoms including kidney failure in vultures, impaired reproduction in mussels, and inhibited growth in algae.

The US Environmental Protection Agency states that it is concerned about growing number of pharmaceuticals in water.  According to Ben Grumbles, assistant administrator for water at the US EPA, the agency has now developed new methods to “detect and quantify pharmaceuticals” in waste water. ''We realize that we have a limited amount of data on the concentrations,'' he said. ''We're going to be able to learn a lot more.''

According to the NY Times, however, only one of the hundreds of chemicals identified is being considered for regulation :

"While Grumbles said the EPA had analyzed 287 pharmaceuticals for possible inclusion on a draft list of candidates for regulation under the Safe Drinking Water Act, he said only one, nitroglycerin, was on the list. Nitroglycerin can be used as a drug for heart problems, but the key reason it's being considered is its widespread use in making explosives."

But despite their concern that people may be making bombs from their tap water, the EPA insists that American drinking water is some of the safest in the world.