Legal Commentary

One of my students recently sent me a link to an article about a method developed by researchers at Oregon State University and the University of Washington to measure levels of drug by-products in sewage.  Apparently, researchers can easily test for all sorts of substances, including crystal meth, cocaine, and marijuana.  So far, scientists have done testing in waste water treatment plants in about a dozen cities across the United States.  Over a 24-day period, folks in these spots held steady throughout the work week with respect to their use of methadone and methamphetamine, but liked to indulge a little with coke on the weekends. 

Right now, test results will aid in assessing groups, not individuals.  But what happens when we can trace by-products of illegal substances to neighborhoods? Or to a street or a block? Or to a house? Is this like garbage left out on the curb? Or does one have a reasonable expectation of privacy in what he flushes down his toilet?