Research has demonstrated that microbial counts can reach < 200, 000 colony-forming units (CFU/mL within 5 days after installation of new dental unit waterlines, and levels of microbial contamination < 106 CFU/mL of dental unit water have been documented. These counts can occur because dental unit waterline factors (eg, system design, flow rates and materials) promote both bacterial growth and development of biofilm.
Although no epidemiologic evidence indicates a public health problem, the presence of substantial numbers of pathogens in dental unit waterlines generates concern. Exposing patients or DHCP to water of uncertain microbiological quality, despite the lack of documented adverse health effects, is inconsistent with accepted infection control principles. Thus in 1995, ADA addressed the dental water concern by asking manufacturers to provide equipment with the ability to deliver treatment water with < 200 CFU/mL of unfiltered output from waterlines. This treshold was based on the quality assurance standard established for dialysate fluid, to ensure that fluid delivery systems in hemodialysis units have not been colonized by indigenous waterborne organisms.
Standards also exist for safe drinking water quality as established by EPA, the American Public Health Association (APHA), and the American Water Works Association; they have set limits for heterotrophic bacteria of < 500 CFU/mL of drinking water. Thus, the number of bacteria in water used as coolant/irrigant for nonsurgical dental procedures should be as low as reasonably achievable and, at a minimum, < 500 CFU/mL, the regulatory standard for safe drinking water established by EPA and APHA/AWWA.