The separation of clean water and sewage is mainly to separate high-polluted water from non-polluted water or low-polluted water and treat them according to their quality to reduce the amount of discharged pollutants and reduce the cost of water treatment. Clean water and sewage are a relative concept, closely related to raw water quality and discharge standards.

Rainwater and sewage diversion is a sewage discharge method that separates urban sewage from rainfall runoff and uses a drainage pipe for discharge or subsequent treatment. The rainwater can be directly discharged to the river through the rainwater pipe network, or can be used as landscape water and municipal water after natural precipitation; The sewage needs to be collected through the sewage pipe network and sent to the sewage treatment plant for treatment. The water quality reaches the corresponding national or local standards before being discharged into the river. The diversion of rainwater and sewage is convenient for rainwater collection and centralized management and discharge, reducing the impact of water volume on the sewage treatment plant, avoiding the pollution of sewage on the river and groundwater, and ensuring the treatment efficiency of the sewage treatment plant.