An investigation has found that drinking water for at least 41 million Americans contains a vast array of pharmaceuticals, including antibiotics, anti-convulsants, mood stabilizers and sex hormones.

The Associated Press conducted the probe, which detected drugs in the drinking water supplies of 24 major metropolitan areas - from Southern California to Northern New Jersey, from Detroit to Louisville, Kentucky.

The report from the AP said the concentrations of these pharmaceuticals are tiny, measured in quantities of parts per billion or trillion, far below the levels of a medical dose, but the presence of so many prescription drugs - and over-the-counter medicines like acetaminophen and ibuprofen is heightening worries among scientists of long-term consequences to human health.

Water providers rarely disclose results of pharmaceutical screenings, unless pressed, but despite the findings, utilities insist their water is safe, said AP.

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.

The five-month inquiry 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 50 largest cities in the US, along with a dozen other major water providers, as well as smaller community water providers in all 50 states.

The AP’s investigation also indicates that watersheds, the natural sources of most of the nation’s water supply, also are contaminated.

“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.