This is interesting!
Day to Day, April 17, 2008 · In Oregon, a team of scientists is making an ambitious attempt to figure out which illegal drugs residents are using. They need only one teaspoon of sewage to administer a citywide drug test. The relatively new field of science is called "sewage epidemiology" and it has a range of practical applications.
http://www.npr.org/templates/player...89808274&live=1