Overview: The United Nations in March 16, 2003 "The Third Water Forum Conference " held before the latest report released on 180 countries and regions, ranking the state rich in water resources, China has an average of nearly 2260m3 of water per person per year Statistics ranked 128. Temporal and spatial distribution of water resources exist large differences in the characteristics of more than 600 cities in more than 400 serious water shortage, the more serious water shortages over 110 cities, China's total 6.0 billion urban water m3. And with economic development, "three wastes" a large number of emission pollution of surface water and groundwater. According to 2003, "China Water Resources Bulletin "shows: In 2003, the country's industrial and municipal waste water in the total amount of 46 billion T, 4.7% over the previous year. The industrial waste water emissions 21,240,000,000 T, increased by 2.5% over the previous year; urban domestic sewage discharge 24760000000 T, an increase of 6.6% over the previous year. Considerable part of the industrial wastewater in China and 90% of untreated sewage discharged directly into receiving water bodies, a direct result of water pollution.
　　Due to industrial wastewater and domestic sewage discharge wanton, resulting in more than 80% of surface water and groundwater contamination. Experts have warned: "After 20 years our country will not find potable water. " Based on satellite photographs of hundreds of lakes are drying up, also lost some local rivers. Water pollution, worsening water pollution, groundwater overdraft and water use efficiency is low, further exacerbating the limited water supply and demand.
 Faced with this grim reality, to ensure healthy and sustainable economic and social development, and ensure the sustainable use of water resources, water reuse is imperative.

The so-called water, the sewage treatment plant will be collected sewage, industrial wastewater, stormwater and other urban sewage, the sewage plants in the conventional activated sludge process through, to remove organics, heavy metals and other purposes, so that the sewage to river water quality Lake emission standards, and then to the depth of the water treatment plant, after coagulation, sedimentation, filtration, disinfection process, or the use of traditional membrane technology advanced treatment, resulting in the water as the water. Water source in accordance with the "design of building water"(GB50336-2002) and "wastewater reclamation and reuse design"(GB0335-2002) were divided into high-quality miscellaneous drainage and sewage treatment, the specific type and select the order:

 1) Bathroom, public bathroom bath and shower drainage;
 2) Wash water;
 3) Air-conditioning cooling water drainage system;
 4) Condensate;
 5) The swimming pool of sewage water;
 6) Laundry drainage;
 7) The kitchen drain;
 8) Flushing water.
Generally not a single water source in the water, most of the three possible combinations:
 1) Toilet water, shower water, cooling water called quality miscellaneous drainage, should be preferred;
 2) A life outside of flushing water as mixed water drainage;
 3) Sewage treatment, that is the general term for all the water of life, this quality is the worst.　　

Water used for flushing, road cleaning, fire fighting, urban greening, vehicle washing, construction and other miscellaneous water quality, according to "urban recycling urban miscellaneous water quality"(GB/T18920-2002) in the class standard for urban miscellaneous water Implementation.
 Water used for landscape and environmental water, the water quality should meet the national standard "of urban recycling water for landscape and environmental quality"(GB/T18921-2002) requirements.