Dental Unit Waterlines: Municipal Tap Water and Why it Should be Avoided

Sponsored: Sterisil

By Jerod Mendolia, marketing assistant, and Reid Cowan, director of marketing, Sterisil

It’s no secret in 2018 that dental unit waterline (DUWL) cleanliness is important. Every trade publication, tradeshow and continuing education summit offers some sort of crash course on the subject. The bacteria problem is widespread and omnipresent regardless of the practice type or equipment employed. If it runs water, the potential to be a problem exists. Given their nature, dental waterlines will grow bacteria beyond the 500 colony forming units per milliliter drinking water standard without some level of shock and maintenance.

Opportunistic bacteria and the subsequent biofilm they produce are everywhere in the natural world. Every dental unit in use today employs a network of tubing to deliver both air and water to the handpieces. The typical tubing used in a dental chair is narrow in diameter and low in volume. This proportional relationship means the internal surface area is much greater relative to the volume of water flowing through the tubing. The smaller the tubing diameter, the larger the internal surface. This large volume of surface area gives bacteria and biofilm plenty of room to establish themselves.

Bacteria and pathogens are opportunists, and they will exploit the nature of dental tubing to their advantage. According to The Organization for Safety, Asepsis, and Prevention (OSAP), “This proportional increase in the amount of potential biofilm relative to a given water volume is one of the major factors influencing dental water quality in unrelated systems.[1]” Once biofilm are established, they can be difficult to eliminate. If left unchecked, biofilm will exhibit a resistance to common disinfectants, making the situation even more problematic[7]. Consider other growth factors unique to dental systems, such as water temperature, flow rates and frequent stretches of stagnation. The culmination of all these factors allows the bacterial load in the waterline to exceed the CDC and EPA drinking water standard of 500 CFU/ml.

So why is this a problem? According to OSAP, “As many as nine potentially pathogenic organisms associated with opportunistic wound and respiratory infections have been isolated from dental unit water systems.”[1] When coolant and irrigant water is used in conjunction with a high speed dental handpiece, the contaminated water is aerosolized along with the bacteria. Now you really have a problem! If patients or the dental team inhales these water droplets, they’ve now been exposed to whatever was growing in the dental unit. There’s also the good old fashioned way of exposed tissue (or dental pulp) being infected when the site is irrigated with contaminated water. Either way, serious infections can be the result of a contaminated DUWL. So how can clinicians mitigate these risks? They can start with the water being supplied to the dental practice.

Most clinicians are not aware that municipal tap water could be contributing to their bacteria problems. Public water works that deliver municipal tap water are prone to contamination and breaches in their own water quality standards. A common watermain break or leak presents an opportunity for pathogens to gain access to the public works. According to a 2012 report, these types of failures have been the cause of several bacterial and viral outbreaks of Salmonella, Campylobacter, Shigella, E. coli O157:H7, Cryptosporidium, Giardia and Norovirus[2,3].

As of 1971, the Centers for Disease Control and Prevention (CDC), U.S. Environmental Protection Agency (EPA) and the Council of State and Territorial Epidemiologists (CSTE) have been tracking and quantifying these waterborne disease outbreaks in the United States. The most interesting insight from the data they provide is that over the 36-year period from 1971 to 2007, “a trend analysis found a statistically significant decrease in the annual proportion of reported deficiencies that were associated with the inadequate or interrupted treatment of water by public water systems[4].” Conversely, the amount of outbreaks related to flaws in premise plumbing have increased in that time[4].

Privately managed water treatment – or premises treatment – are technically outside the jurisdiction of a water utility. The liability falls to building managers to implement a strategy for maintaining waterlines after the meter. According to the American Society for Microbiology, “Health care settings, such as hospitals and nursing homes, were the second most common outbreak location in community systems, highlighting the need for continued vigilance to ensure provision of safe water to locations that serve populations that are more vulnerable, such as hospitalized patients or nursing home residents with preexisting medical conditions.”[4] For dental professionals in large healthcare facilities, it is certainly worth speaking with building managers about the plans for water treatment within the building. Systems of water quality monitoring and intermittent testing should be in place where the consequences could be serious.

Maximum chemical control
In 2015, reports began to circulate that a cluster of Mycobacterium abscessus infections had been identified in Atlanta, Ga. after nine pediatric patients were hospitalized in the same facility. The CDC reported that the Georgia Department of Public Health (GDPH) initiated an investigation, which revealed that all of the patients (between the ages of 3-11) had previously undergone a pulpotomy procedure at the same dental clinic. Upon visiting the clinic to evaluate their infection control policies, GDPH staff indicated the practice used tap water for irrigation during the pulpotomies. The report also indicated the practice lacked any level of monitoring or disinfection efforts as directed by the chair manufacturer. The report concluded that all seven operatories had bacterial counts above the 500 colony forming unit (CFU) drinking water standard and M. abscessus was identified in all samples[5].

If a dentist intends to use their municipal water for dental water – and, yes, there is a difference – it would be advisable to have some level of water quality analysis before selecting the product. Variations in tap water quality are virtually infinite and, therefore, the dental practice should not rely on tap water for consistent disinfection results. The presence of municipal disinfectants and additives, such as chlorine and fluoride, complicates things further if the practice is trying to manage the chemistry, as it should to get the best results. By failing to do so, the dental practice has a concoction of different chemicals and additives mixing in the waterline. The byproduct of these unwanted mixtures is called precipitates, and their presence indicates the diminished effectiveness of whatever exists in the water to control microbes.

So what is the solution? To attain maximum chemical control, distilled quality water is best. That said, distilled water from a distiller is not always optimal for dental water. The nature of distillation requires that one heat the water to remove impurities. This hot distillate is now primed for recolonization by bacteria. Without immediate waterline treatment, this water will most assuredly be contaminated. Without the presence of a continuously present residual disinfectant, that water will most assuredly be a breeding ground for bacteria. Distillers themselves are often the source of contamination for many offices, as once the storage tank is contaminated the water is then distributed along with the bacteria to the entire office.

The best strategy is a point-of-use purification system using deionization to remove all the impurities without heating the water. Ultraviolet disinfection can then be employed to drastically lower the existing bacterial load with proven effectiveness [8]. The water would then receive a low concentration of a residual disinfectant. The final product is water that is neutral in pH, contains less than 10 ppm total dissolved solids, is disinfected and contains some variety of residual disinfectant.

Now the water is pure and bacteria free. So the treatment process is complete, right? Not even close! We haven’t gotten to the most important part – the dental water use protocols. Without sound operating protocols, everything the dental practice has done up to this point would be for not.

Dental water use protocols
Manufacturers spend unmentionable amounts of money on development, EPA registration and validation for their products. The EPA label will run down all the necessary steps needed to get the advertised disinfection level. Clinicians should not go rogue on these protocols! When it comes to quality assurance (QA), OSAP recommends procedures that flush out user error[6]. Let’s face it, people can make mistakes. Minor investments like TDS hand meters will allow some level of protocol QA. For example, when using distilled water in their bottles, clinicians should randomly check the TDS count and ensure the result is less than 20 ppm. If it’s greater than 20 ppm, they can assume the water in that bottle is not distilled and that someone has botched the procedure for refilling it. Protocol consistency and quality failsafes are fundamental to getting all of this waterline stuff done right. Consistency leaves nothing to chance. This is also important, as manufactures design their products to work within certain parameters. We’ve already discussed the variability in water chemistry across the spectrum. Deviations in protocol, like the example above, could mean the dental practice is no longer operating within those parameters and, subsequently, it may have contributed to contamination in the unit.

So what is compliance under the current standards? The acceptable standard set by the CDC and the ADA for bacterial content in a dental unit is ≤500 CFU/ml. Compliance is not a state of mind; it’s a state of being. The notion that purchasing a product and following the instructions puts one in compliance is just wishful thinking. A complete and thorough waterline assessment performed by a 3rd party lab specializing in dental water microbes will provide all the information necessary. TDS, pH, and HPC counts in CFU/ml are the general markers of waterline cleanliness. These test results can be used to make adjustments to the waterline protocol or confirm that clinician’s efforts are having the desired effect. It can be something as simple as a change in the daily staff use or as extensive as a complete overhaul of the regimen at large.

Contaminated dental unit waterlines are a real threat to patient and staff safety. Their design, the nature of dental procedures and the conditions within the dental operatory prime them for bacterial colonization. We know the problem can be exacerbated by using municipal water instead of purified or distilled water, and the case data proves this point. The most important takeaway from this piece is that whatever clinicians do, they should be consistent. They should read manufacturers guidelines and follow them, as there may be something they’ve been missing. When they feel like everything is going well, they shouldn’t assume it is. Rather, they should order a test and know for sure. If clinicians miss the mark, they should reevaluate their plan, retrain their staff and retest to confirm the change. Attaining the <500 CFU/ml standard in dental effluent water is the culmination of forethought, execution, consistency and vigilance. No excuses!


  1. Berdnash, Helene, et al. “Dental Unit Waterlines: Check Your Dental Unit Water IQ.” Dental Unit Waterlines – OSAP,
  2. Ingerson-Mahar, M.; Reid, A. Microbes in Pipes: The Microbiology of the Water Distribution System A Report on an American Academy of Microbiology Colloquium; ASM Academy: Boulder, CO, USA, 2012; p. 26.
  3. Ramírez-Castillo, Flor, et al. “Waterborne Pathogens: Detection Methods and Challenges.” Pathogens, vol. 4, no. 2, 2015, pp. 307–334., doi:10.3390/pathogens4020307.
  4. Craun, Gunther F., et al. “Welcome to CAB Direct.” CLINICAL MICROBIOLOGY REVIEWS, vol. 23, no. 3, July 2010, pp. 507–528.,
  5. Peralta, Gianna, et al. “Morbidity and Mortality Weekly Report (MMWR).” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 25 Aug. 2017, – Dental Unit Waterlines
  6. Bridier, R. Briandet, V. Thomas & F. Dubois-Brissonnet. “Resistance of bacterial biofilms to disinfectants: a reviewBiofouling Vol. 27 , Iss. 9,2011
  7. Chevrefils, Gabriel, et al. UV Dose Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa and Viruses. UV Dose Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa and Viruses, Trojan Technologies Inc., 2006.