An anecdote from a student over drug use at the University of Puget Sound led one professor to test sewage in an effort to gauge the use of illegal drugs. "The amphetamine levels go through the roof during finals," says chemistry professor Dan Burgard in an interview with Gizmodo. Sewage tests in Europe have now allowed scientists to map exactly where drugs are consumed, covering entire populations and cities. While scientists can pinpoint usage spikes of cocaine and ecstasy in London, and the increase of marijuana use in Italy, legal and ethical concerns have arisen over police potentially testing wastewater. Gizmodo takes a closer look at the process, leaving questions over your right to privacy when you flush your toilet.