Wastewater, or sewage, is water people have used, either at home in their bathrooms, kitchens, laundry rooms, and yards or in industrial operations like agriculture or manufacturing. In the United States, sewage treatment plants process about 34 billion gallons of wastewater a day.
Untreated wastewater contains mostly water by volume. It also contains numerous impurities that make the water unsafe for reuse or to discharge back into the environment.