“Everyone knows how a drug test works: You urinate into a cup and your employer (or prospective employer) has the sample tested to see if you’ve been using any illegal substances. This year, though, Jennifer Field, an environmental chemist at Oregon State University, experimented with an unusual variation on this process. She found out what illicit drugs the population of an entire city was ingesting.

How? By collecting and then testing water from the city’s sewage-treatment plant. Since all drug users urinate, and since the urine eventually winds up in the sewers, Field and her fellow researchers figured that sewer water would contain traces of whatever drugs the citizens were using.” (New York Times Magazine Year in Ideas)