Every year in the United Kingdom we spend upwards of £10bn (€13bn; $20bn) on medicines. And where do they go? Down the drain, literally. Out of the bladder, through the sewage system, and into the rivers. Some drugs—unwanted or out of date—bypass the bladder and are flushed straight down the toilet. Either way, does it matter? To fish and other organisms living in the thin chemical soup that emerges from the sewage treatment plants it does; there is evidence of harm to aquatic ecosystems, particularly from endocrine disrupting chemicals such as ethinylestradiol, which is used in many oral contraceptives. For humans, protected by the purification technology that river water goes through before it re-emerges from the kitchen tap, the answer might seem to be no. But how well founded is this assumption?

In March this year the US news agency Associated Press announced the results of an investigation into drugs and the water supply.1 “A vast array of pharmaceuticals—including antibiotics, anti-convulsants, mood stabilizers and sex hormones—have been found in the drinking water supplies of at least 41 million Americans,” it claimed. The inquiry found trace quantities of these drugs in the drinking water supplies to 24 metropolitan areas from southern California to northern New Jersey.

A typical press scare? Maybe. But the evidence was enough to prompt two US politicians to arrange a senatorial hearing. This took place on 15 April and saw the US Environmental Protection Agency lambasted for its alleged complacency.2 The agency responded that it was taking the issue seriously, and that it was “drastically expanding the scope” of its testing of drinking water across the nation.

In Europe too there have been reports of medicines in drinking …