Wastewater is largely treated by publicly owned treatment works (POTWs). A smaller number of private facilities, such as industrial plants, also treat wastewater. A POTW is a device or system used to treat, recycle, or reclaim municipal wastewater or industrial liquid waste that is owned by a state, municipality, special sewer district or other publicly owned and financed entity. There are over 16,000 POTWs in the U.S. and like drinking water, there are fewer large wastewater utilities (21%) than smaller utilities (79%).

• 10 percent of the population receive sanitation services from small wastewater utilities that treat less than 1 million gallons per day (MGD).
• Utilities that treat more than 1 MGD are considered medium size (1-10 MGD), and large size utilities (10 or more MGD) provide wastewater treatment to the other 90 percent of the population served.