Wastewater treatment is to use physical, chemical and biological methods to treat the wastewater, so as to purify the wastewater, reduce pollution, and reach the discharge standard when the wastewater is discharged.

Wastewater is not just sewage. All the water used in the home that goes down the drains or into the sewage collection system is wastewater. This includes water from baths, showers, sinks, dishwashers, washing machines, and toilets. Small businesses and industries often contribute large amounts of wastewater to sewage collection systems; others operate their own wastewater treatment systems.