A Mayo Clinic study issued in June 2013 found that nearly 70 percent of Americans take one prescription drug, up from 48 percent in 2007-2008. According to the Centers for Disease Control and Prevention, health care providers in the United States wrote 259 million prescriptions for painkillers in 2012, enough for every American adult to have a bottle of pills. Municipal wastewater treatment plants are not designed to treat complex drug compounds that end up in the sewer system after being flushed down toilets and sinks. As a result, drugs can pass through wastewater treatment systems and contaminate receiving waters.