Objective:To identify the potential factors influencing the water quality of dental unit waterlines(DUWLs) by examining water samples collected from dental chair units(DCUs) from different departments, brands and service lives. Methods: Water samples were collected from 33 DCUs at the Affiliated Hospital of Stomatology, NJMU. Before patients arrived, a water sample of approximately 50 mL was collected from each DCU using a three-in-one air/water syringe. The water sample was diluted, and 0.1 mL of a prepared sample was spread on a sterilized R2A plate. After incubation, the number of microbial colony-forming units per millilitre was quantified with an automatic colony analyser. Statistical analyses were performed using SPSS 19.0 software. Results: According to the statistical analyses, no significant differences of the water quality were found in SIRONA C8+ with different service lives. However, the comparison of the water quality in different departments and brands showed significant difference(P≤0.05). SIRONA C8+DUWLs and DCUs of Endodontics Departments provided better quality water. Conclusion:Different service lives did not significantly influence the water quality of DUWLs. However, different DCU brands and different departments can influence the water quality. In this study, SIRONA C8+DUWLs and DCUs of Endodontics Departments provided better quality water.