Abstract: Abstract: The quality of drinking water system has a significant impact on health and performance of poultry. The drinking water system quality has been considered an important factor for pathogens and epidemic infection entry into poultry buildings. It is critical therefore to control the bacteria concentration to ensure the bird’s well-being and reduce the mortality. The nipple drinking system has been mechanization in large-scale, which has reduced the need for manual labor and decreased the water leakage. However, it is difficult to clean the nipple drinkers and water pipes because the nipple drinking system is a closed system. Also, it is hard to prevent and control the biofilm of water pipe, due to there are a wide variety of bacterial transmission routes. It is a common practice that multiplex vitamin solution, vaccine and drug are added in the water drinking system. However, such practice could cause the high level of bacteria and microorganisms in the system, polluted water, and clogged up nipple drinkers. Thus, we need to find solutions to solve issue of how to control the bacterial concentrations of nipple drinking system to ensure a safe drinking water for birds so that the health of birds can be improved and the use of drugs in production can be reduced. Slightly acidic electrolyzed water (SAEW) has been widely used in agricultural production fields, including disinfection of the vehicle tire surface, human, eggs, spraying layer farm, etc., and has the advantages of possessing broad-spectrum antimicrobial activity. Slightly acidic electrolyzed water is generated through electrolysis of dilute salt solution and hydrochloric acid. But there is no information found in literatures about research on its bactericidal efficacy of drinking system using slightly acidic electrolyzed water in layer houses. In this paper, we studied effect of the washing drinking system, adding multiplex vitamin solution and slightly acidic electrolyzed water on the logarithm of bacterial concentrations in drinking water system. As well, variation of slightly acidic electrolyzed water residue chlorine during test period and the schematic diagram of adding slightly acidic electrolyzed for drinking water system in laying hen house was studied. The experiment was conducted in a large-scale layer hen poultry house located at Henan province. The results showed: 1) Before adding multiplex vitamin solution, the logarithm of bacterial concentrations in drinking water system was (2.81±0.06) lg(CFU/mL). For 4、6、12、24、36、48、72 h after adding multiplex vitamin solution, the logarithm of bacterial concentrations in drinking water system were respectively (3.09±0.06)、(2.96±0.04)、(2.98±0.05)、(3.02±0.06)、( 2.95±0.03)、(2.97±0.11)、( 2.93±0.04)、and (2.95±0.06) lg(CFU/mL). The logarithm of bacterial concentrations were respectively increased by 9.96 %、5.33 %、6.04 %、7.47 %、4.98 %、5.69 %、4.27 %、4.98 %. Adding multiplex vitamin solution led to the bacterial concentrations decrease;2) By conventional method of cleaning nipple drinking system can reduce the bacterial concentration to a certain degree and decrease the suspended matter, but cannot make bacterial concentrations reached the national standard.3) Before adding slightly acidic electrolyzed water, the bacterial concentrations was far higher than the bacterial concentrations standard for drinking water in China. After addition of the 0.3 mg/L slightly acidic electrolyzed water for 24 hours, the bacterial concentrations were reduced to below national standard and decreased by 34.7%, and the logarithm of bacterial concentrations in drinking water system were (1.83±0.05) lg(CFU/mL) . The results indicated that SAEW has a great potential to be used as effective disinfection method for the drinking water system of layer hen houses. Results of this study provide an effective measure to reduce bacterial concentrations of poultry drinking water system and the study contributes to ensuring the bird’s well-being and reducing the mortality.