People like to think of their water as pure. The reality is that every drop on Earth has been recycled countless times, through oceans, aquifers, rivers, lakes -- and fellow human beings.

A massive study by The Associated Press published Monday drove that last point home. The study, which reviewed water utility databases and government data, uncovered an unsettling reality: Clearly identifiable pharmaceutical compounds were found in the water supplies of 24 major metropolitan areas and numerous smaller water utilities. Among the drugs: Painkillers, sex hormones and antibiotics. Rural consumers who rely on wells for their water aren't necessarily safe: Some wells have tested positive for caffeine, a clear marker indicating the presence of human-generated sewage in groundwater, possibly the result of failed septic tanks nearby.

The contamination is probably more widespread than the AP study suggests, since many utilities don't test their drinking water for pharmaceuticals. Testing is far less common among small and medium-sized water utilities than big ones, but many of the nation's largest utilities -- including utilities in Chicago, Baltimore and New York City -- don't test either. And even those that test often look only for a few selected drugs. Meanwhile, water-quality testing in the nation's water bodies shows increasing levels of many common medications, such as birth-control pills and blood-pressure drugs.

Most scientists say these compounds don't present any danger to people drinking treated water -- at least not at the levels found in most utilities' tests. But others point to research showing troubling effects of very small amounts of specific medications on fetal development. And biologists have said conclusively that human-induced contamination, including medications and other chemicals, can be responsible for sexual mutations in fish and other animals.

This isn't the first time the question of drugs in the water supply has been raised. The first studies -- identifying aspirin, caffeine and other substances in groundwater -- are nearly 20 years old. But the AP study is capturing the attention of public officials in a way that suggests they're ready to start tackling the issue of drugs and other chemicals in the water supply before it becomes a problem. Tuesday, U.S. Sen. Frank Lautenberg, chairman of the Transportation, Safety, Infrastructure Security and Water Quality Subcommittee, and Sen. Barbara Boxer, chair of the Senate Environment and Public Works Committee, both said they plan to hold hearings on the issue. The attention is timely, if not overdue.

The first, and least expensive, step is to let the sunshine in: Water utilities that currently test for pharmaceuticals should make that information freely available to their customers, along with more information on the potential impacts of drugs in the water supply. (Many of the cities contacted by The Associated Press initially denied finding pharmaceuticals in their water but were contradicted by records.) The Environmental Protection Agency should add the most commonly found drugs to the list of contaminants that utilities are required to disclose.

But that doesn't help customers of utilities that don't test. Setting nationwide standards about which drugs water utilities should be testing for and figuring out how to pay for those tests (which can be expensive) represents a bigger challenge. But it's one leaders should take seriously. Billions of people rely on the safety of the nation's water supply, and it's worth the effort to make sure their trust is justified.