The latest installment of The Associated Press’ PharmaWater investigation seemed unlikely at the initial story conference: no ready data and seemingly nothing to expose.

Our national investigative team had broken the story this past year that tens of millions of Americans drink from water supplies that test positive for trace pharmaceuticals. They cover the gamut from antibiotics to psychiatric drugs to sex hormones, mostly in the form of unmetabolized medicines excreted by people.

They are found in concentrations far below medical doses, but some aquatic species already have been hurt, and research is raising questions about the effects on humans over decades.

In our second phase of PharmaWater, we reported that millions of pounds of unused drugs also are dumped each year by hospitals and long-term care homes. We knew that other sources exist, but government and industry agreed that factories weren’t a meaningful contributor. They said little product escapes during the manufacturing process.

However, we had read research, mostly from abroad, that challenged that claim. Working as a member of our team, Asia-based medical writer Margie Mason took the next step: She reported that the highest concentration of drugs ever recorded in the environment was measured downriver from a cluster of pharmaceutical factories in India.

AP Investigative Editor Rick Pienciak wanted to know more. We decided to investigate U.S. factories, but the federal government didn’t keep specific data on their pharmaceutical water pollution. The U.S. Environmental Protection Agency does, however, collect data on factory releases of chemicals of many types. As a former medical writer, I previously had recognized one or two scientific pharmaceutical names lurking among hundreds of chemicals in these data, but how to check for all approved drug ingredients? We needed a reliable list of active pharmaceutical ingredients to download and match with the EPA data.

Enter John Parsons, an AP database analyst. Parsons started with a downloaded PDF file of the U.S. Food and Drug Administration's Orange Book, which is a reference guide to approved pharmaceuticals. The frustrating problem was that the active ingredients were buried in each separate entry.

Jeff Donn is a Boston-based member of the Associated Press national investigative team.