Reclaimed water refers to water that after appropriate treatment of wastewater or rainwater reaches certain water quality indicators, meets certain usage requirements, and can be used beneficially. Compared with seawater desalination and cross-basin water transfer, recycled water has obvious advantages. From an economic point of view, the cost of recycled water is the lowest. From an environmental point of view, sewage recycling can help improve the ecological environment and achieve a virtuous cycle of water ecology. "Reclaimed water" is named after Japan. There are many interpretations of the definition of "reclaimed water". It is called "reclaimed water" in sewage engineering and "recycled water" in factories. Water quality is generally used as a mark of distinction. It mainly refers to non-potable water that can be reused within a certain range after urban sewage or domestic sewage has been treated to meet certain water quality standards. The collective name refers to the water that has been deeply purified by urban sewage treatment facilities (including water after secondary treatment and further in-depth treatment in sewage treatment plants and concentrated treated water such as bathing water and vegetable washing water in large buildings and living communities). "Medium water". The quality of its water is between that of tap water (top water) and sewage discharged into pipes (sewer water), so it is also called "remote water". Reclaimed water utilization is also called wastewater reuse. In the United States, Japan, Israel and other countries, a large amount of gray water is used for toilet flushing, garden and farmland irrigation, road cleaning, car washing, urban fountains, cooling equipment replenishment water, etc. It has been nearly 20 years since the term gray water was first used in China in the early 1980s, and it has now been recognized by industry insiders and even some people in water-scarce cities and regions. It was originally called "middle water", coming from Japan, because its water quality and its facilities were between water and sewers. With the introduction of foreign reclaimed water technology, experimental research on domestic pilot projects, advancement of reclaimed water engineering facility construction, development of reclaimed water treatment equipment, research and development of reclaimed water application technology and the establishment and implementation of relevant norms and regulations, gradually A complete set of engineering technologies is formed, just like "water supply" and "drainage", which is called gray water.