中水道系统是输送通过特定设备处理后的生活污水到各个用水点上的一个供水系统。由于这样的供水系统有别于上下水道的功能,其供水水质介于上水(自来水)和下水(城市污水)之间,故称为中水道,处理后的回用水则称为中水。中水道供水一般用于冲厕所、绿化、冲洗汽车、清洁、施工等用水,从而可以达到重复使用水和节水的目的。中水道在国外已有应用。如日本约有200座以上住宅小区使用中水道。仅东京都就有62座 The middle waterway system is a water supply system that delivers domestic sewage that has been treated by specific equipment to each water point. Because such water supply system is different from the function of water supply and sewerage, the quality of its water supply is between that of water supply (tap water) and launching (urban sewage), so it is called the middle waterway. The treated water is called water. The water supply of the watercourse is generally used for toilet flushing, afforestation, flushing the car, cleaning, construction and other water, so as to achieve the purpose of reusing water and saving water. The waterway has been applied abroad. Such as Japan, about 200 or more residential quarters in the waterway. There are 62 in Tokyo alone