This video segment adapted from FRONTLINE: "Poisoned Waters" explains how the Potomac River, like many other rivers, serves as both a drinking water supply and a dumping ground for wastewater. With proper processing, a water recycling system works well. However, water treatment removes only known contaminants; there is a growing concern about "new contaminants," chemicals in the water that are still unregulated but could cause harm to humans and animals.