A standard water treatment system usually consists of a pretreatment unit, a core treatment unit, a post-treatment unit, and auxiliary equipment. These parts work together to ensure that the water quality meets the expected standards.

Although household sewage reuse is not yet popular, this trend is gradually emerging, especially in some states with relatively scarce water resources, such as California, Arizona, and Nevada. Household sewage reuse usually includes two aspects: treatment and reuse of gray water and black water.