Abstract: With the increasing popularity of water purifier and people's attention to drinking water safety, the microbiological safety out of water purifier has become one of the problems which must be solved. Usually, RO water purifiers can effectively remove bacteria. However, there is a potential safety risk of microbial breeding in the pipeline after pure water coming out of membrane to nozzle. To solve this problem, proposes a step-by-step hot water sterilization technology for cold boiled water system of commercial water purifiers made for school. By heating, insulation, heating, and cooling the drinking water pipeline, using relatively less hot water to extend the time of effective sterilization temperature. At the same time, the structure of the outlet solenoid valve is optimized to solve the sterilization blind spots. Through testing and verification, the outlet bacterial colony can be controlled below 5 CFU/100 mL all day, effectively solving the problem of excessive outlet bacterial colonies and ensuring the safety.

Key words: Water purifier, Colony control, Outlet solenoid valve, Step-by-step hot water sterilization