Objective To understand contamination status of dental water in private dental institutions in one district of Beijing, and provide reference for improving dental water quality. Methods From November 1 to 30, 2019, stratified random sampling method was used to select 30 private dental institutions for on-site dental water collection, detection method was in accordance with GB/T 5750.12-2006 Standard Test Method for Drinking Water, judgment criterion was referred to GB 5479-2006 Standard for Drinking Water Quality. Results A total of 264 dental water specimens were collected from 30 private dental institutions, 76 dental water specimens were qualified, with a qualified rate of 28.79%. The median of the tatal number of colonies in water in dental handpiece and water-storage bottle was about 2 000 CFU/mL, the qualified rate of dental handpiece water specimens was higher than that of water-storage bottle (18.33% vs 9.09%); the median of the total number of colonies in water specimens of imported and domestic dental chair units (DCUs) were 255 and 1 750 CFU/mL respectively; qualified rate of water specimens of imported DCUs was higher than that of domestic DUCs(42.39% vs 21.51%); the median of the total number of colonies in tap water and water in water-storage bottle were 400 and 2 100 CFU/mL respectively, qualified rate of tap water specimens was higher than that of water-storage bottle (35.82% vs 12.16%). Conclusion Dental water in private dental medical institutions in this district of Beijing is seriously contaminated, it is suggested that the relevant standards and specifications of dental medical institutions should be formulated as soon as possible, so as to improve the quality of dental water sanitation.