The feed water enters the feed water storage tank, which is designed with a capacity of 8000L and a water consumption of 3-5 cycles in the tank to avoid the breeding of microorganisms of water in the tank. After passing through the heat exchanger (which can effectively prevent the low ro salt absorption rate caused by the low temperature in winter; at the same time, the pretreatment system can be pasteurized), the feed water enters the pretreatment system, which includes multi-media filter, activated carbon filter, softeners, The multi-media can effectively remove large particle solids, suspended solids, colloids, etc., and the SDI value can be less than 3 after being filtered by the multi-media filter; Activated carbon filter can effectively remove free chlorine in water quality, which will be less than 0.01ppm; The softener can effectively absorb calcium and magnesium ions in water, reduce water hardness and protect RO membrane. In the design, the series operation and parallel regeneration are adopted, and each softener can achieve 100% operation effect, considering both the continuity of production and the alternate operation of softeners; Then after 5μm precision filter (to protect the RO membrane from damage); The fresh water after RO1 membrane filtration enters the next stage, and the concentrated water returns to the raw water tank; After the middle water tank, it enters the RO2 through the secondary high-pressure pump. The fresh water of the secondary RO (concentrated water returns to the middle water tank) enters the EDI device for ionization. After the fresh water production is detected according to the conductivity, if it meets the requirements, it enters the purified water tank. If it does not meet the requirements, it returns to the middle water tank.