Now, a twist on that tactic is being employed to monitor the consumption of opioids and other drugs in various cities and towns around the world, according to a fascinating article by Michael Kelly that now appears on Opioid Watch, a brand new online news resource from the nonprofit Opioid Research Institute.

The technique, called “hotspotting,” analyzes an area’s sewage water to measure traces of legal and illegal drugs and track their changes over time. “Wastewater analysis,” Kelly explains, “can reveal the collective drug habits of communities, providing a more accurate picture than self-reported surveys. It can also alert communities to budding problems in their midst at an earlier stage than grim emergency-room statistics and overdose deaths.”

One large European study, for example—which examined sewage from 60 cities in 19 countries—discovered an acute use of methamphetamine in two eastern German cities (Chemnitz and Erfurt), heavy use of cocaine in Zurich and Barcelona, and a notable level of MDMA (ecstasy) use in Amsterdam, Kelly reports.

Seeing what drugs people in a community are really using—and how much—won’t change behavior by itself. But it’s the first step, arguably, in setting up effective interventions.

The story is one of several fascinating discoveries on Opioid Watch, a site curated by Roger Parloff, who for years was a senior writer at FORTUNE and one of the most gifted reporters to have graced these halls. The site also offers breaking news and up-to-date stats on this topic as well as current status reports on litigation and other judicial action. It’s really worth checking out.

This essay appears in today’s edition of the Fortune Brainstorm Health Daily. Get it delivered straight to your inbox.