I think I am late to the game on this, because when I typed into Google “pharmaceutical drugs in tap water,” an old WebMD article – from 2008 – came up: Drugs In Our Drinking Water?, saying:

Ever since the late 1990s, the science community has recognized that pharmaceuticals, especially oral contraceptives, are found in sewage water and are potentially contaminating drinking water.

So, for 20 or 30 years it was known. The article said that the “deputy director for science and technology in the Office of Water at the EPA” was looking at it.

Here’s an article from a couple months ago. They must be still looking at it.

Environmental Pollution With Psychiatric Drugs, World Journal of Psychiatry, October 2021

Currently, wastewater is considered the most important source of drugs to the environment. Furthermore, the currently available wastewater treatment plants are not specifically prepared to remove drugs, so they reach practically all environmental matrices, even tap water.

As drugs are designed to produce pharmacological effects at low concentrations, they are capable of producing ecotoxicological effects on microorganisms, flora and fauna, even on human health.

It has also been observed that certain antidepressants and antipsychotics can bioaccumulate along the food chain.

Possible solutions consist on acting at source, using medicines more rationally, eco-prescribing or prescribing greener drugs, designing pharmaceuticals that are more readily biodegraded, educating both health professionals and citizens, and improving coordination and collaboration between environmental and healthcare sciences.

Besides, end of pipe measures like improving or developing new purification systems (biological, physical, chemical, combination) that eliminate these residues efficiently and at a sustainable cost should be a priority.

“using medicines more rationally”
What does that mean? Are there instances when a physician is not prescribing rationally?

When I thought of chemical pollution, I was more focused on pesticides, industrial chemicals, plastics. Drugs hadn’t been at the top of that list. Welp.