This is the first study in Jordan to determine the degree of bacterial contamination of water outlets from high-speed drill and air/water syringe waterlines in dental clinics. Total heterotrophic bacterial counts (HPC), in addition to Pseudomonas aeruginosa, and Legionella pneuomophila as opportunistic pathogens were investigated in the source water, high-speed drill and air/water syringe waterlines. Heterotrophic bacterial counts (HPCs) exceeded 500 CFU/ml in 26% of the water sources supplying the units. Pseudomonas aeruginosa was detected in 12% of the source water sample supplying the dental unit in a range of 1-500 CFU/ml. Concentration ranging between 1-100 CFU/ml of Legionella pneuomophila of serogroup 1 was detected in 20% of source water samples. This study has shown that dental unit waterlines were not complying with International Drinking Water standards for heterotrophic mesophilic bacterial count (>500 CFU/ml), nor with the American Dental Association guidelines (>200 CFU/ml). The presence of Pseudomonas aeruginosa and Legionella pneuomophila is an indication of low water quality in dental unit waterlines.