More than 20 studies of European wastewater over the past decade have produced some interesting findings about the drug habits of residents of some of the continent's biggest cities. For instance: "In London, cocaine and ecstasy spike on weekends while methadone is used more consistently," writes Brian Bienkowski. While in Zagreb, Croatia, "marijuana and heroin were the most commonly found illicit drugs, but cocaine and ecstasy showed up more frequently on weekends."
Though relatively novel (especially in the U.S.), the practice of testing sewage to gauge illegal drug use has begun to grow thanks to technological advancements and doubts over the quality of survey results. But the technique has raised raised legal concerns over privacy expectations.
"Legal issues aside, there are some ethical concerns, said Jeremy Prichard, a professor of law at the University of Tasmania who wrote an article about the ethics of testing sewage for drugs. Since it's about illegal drugs, the research could attract media attention and stigmatize certain communities, Prichard said. He supports guidelines for researchers to protect people and communities."