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It’s a season of change for dental unit waterline infection control

Aug. 1, 2020
It’s not often during one’s career that the guidelines and clinical foundations one practices are overhauled.

It feels like the normal routines of our personal and professional lives were turned upside down overnight. It’s not often during one’s career that the guidelines and clinical foundations one practices are overhauled. The last time that radical changes in health-care workers’ infection control procedures were implemented was in 1987. It was in the midst of the HIV/AIDS epidemic, when the Centers for Disease Control and Prevention (CDC) introduced universal precautions.1 

As the world navigates the novel COVID-19 pandemic, it has forced the dental field to reexamine infection control procedures and how best to minimize pathogens from all areas of dental offices. Dental unit waterlines (DUWLs) should be included in this examination. 

Thousands of dental office doors were closed for weeks after the federal government and the majority of states implemented guidelines that restricted nonemergent dental care. This occurred when COVID-19 was declared a pandemic by the World Health Organization on March 11, 2020. When dental care is greatly reduced or stopped, additional steps most likely need to be taken to maintain waterline safety. 

Whether an office’s delivery system is a direct connection to the municipal water supply or from a dental bottle, it is important to refer to the dental unit manufacturer’s recommendations prior to implementing a product or procedure. Whichever delivery method is used, there is the ability to test and treat the waterlines, and the costs to implement these protocols may vary.

DUWLs present a complex scenario for dental offices due to the size and design of waterlines. These are the main suppliers of water to handpieces, ultrasonic scalers, and air-water syringes. According to an article in Dental Products Report, multiple factors affect the microbial infiltration of DUWLs due to the, “small-diameter waterlines, low-flow rates, long periods of stagnation, improper waterline termination, and occasional backward contamination from the patient to the delivery system.”2

 The small diameter of waterline tubes makes this area susceptible to harboring bacteria. Once this biofilm is present, it can replicate very quickly. For example, Legionella pneumophilia tends to thrive in biofilm and can be a challenge to eradicate.3 While DUWLs cannot be sterilized, the lines or self-contained bottles can be cleaned and disinfected. Proper disinfection and cleaning procedures, in addition to testing bacterial levels, will help ensure that the waterlines remain at a low bacterial level. 

So, what is the acceptable bacterial load for DUWLs? Dental unit water must meet the Environmental Protection Agency’s (EPA) drinking water standard, which is measured by a heterotrophic plate count (HPC) of less than or equal to 500 colony-forming units (CFU) per milliliter for routine dental care.4 It should be noted that these levels are not acceptable for surgical procedures, and the American Dental Association (ADA) recommends using sterile water or saline for these procedures. Simply stated, heterotrophic bacteria’s food source is organic carbon, which is found in all water sources. But when the numbers of heterotrophic bacteria per mL increase, more dangerous bacteria such as Legionella or E. coli can thrive.

The potential presence of more dangerous types of bacteria validates testing DUWLs in dental practices. By performing scheduled monitoring of DUWLs, practices can ensure that they’re maintaining the EPA drinking water standard. While an increase in microbial levels may not pose as high of a risk to healthy populations, it does put immunocompromised and elderly people at risk. Historically, there have been a small number of cases of illnesses from DUWLs. But a small number does not negate the importance of implementing standards and protocols. 

In 2016, 57 patients of a pediatric dentist in Anaheim, California, became ill with mycobacterial infections after pulpectomies were performed on them using untested tap water. There was a similar incident in Georgia in 2015 when approximately 12 pediatric dental patients became ill after dental treatment.6 Not only does routine testing and regular DUWL maintenance protect patients, it also protects dental health-care providers from waterborne pathogens that become aerosolized during procedures, and from equipment that uses the waterline. Waterline testing is recommended by the CDC, and as recently as 2018 states such as California and Washington implemented higher DUWL standards that exceeds CDC recommendations.7

Current recommendations and tips from the FDA and CDC

  • Establish a written protocol for managing and testing DUWLs.
  • Implement the use of filters, filtration systems, and sterile water delivery systems when needed.
  • If using self-contained dental bottles, empty water bottles at the end of each day and purge water from all waterlines.
  • Flush water through the lines between each patient for approximately 30 seconds. This will help flush out any bacteria that may have back-flowed into DUWLs during dental procedures.
  • Room temperature water should be used to fill self-contained dental bottles. Warm water facilitates bacterial growth.
  • Be cognizant of the smell, taste, and color of the water in order to monitor for signs of biofilm formation.
  • If DUWLs have not been used for an extended period of time, the manufacturer’s manual should be consulted to determine if the DUWLs need to be shocked prior to use.
  • Routinely monitor and test water quality of DUWLs.
  • Adhere to maintenance and product recommendations that are made by the dental unit manufacturer.4

The CDC currently does not mandate DUWL testing; it is simply a recommendation. Without testing DUWLs, dental offices are potentially unaware of the status of their water quality. Test kits can be obtained from companies that carry commercial water testing kits or from laboratories. Dental offices should refer to the manufacturer’s manual for their specific dental units for product recommendations. 

Testing and routine waterline maintenance are just as important now as they ever were. According to the ADA, when evaluating which test kit is best for your practice, it is best to look for a product that has a “well-designed water quality indicator and should accurately detect a wide concentration range and type of aerobic mesophilic heterotrophic waterborne bacteria within a reasonable incubation time at room temperature.”5 Without routine monitoring, it is difficult to determine if the waterlines are at an acceptable drinking water level, which would mitigate the efforts to have a quality water source for patients.

Quick checklist for dental staff

  • When were the DUWLs last tested and who is responsible for monitoring testing?
  • If the DUWLs have gone unused for a period of time, is a shock treatment required?
  • Are waterlines being flushed at the beginning and end of each day as well as between patients?
  • If dental bottles are being used, is the water being purged from the lines?

In this current health climate, health-care providers need to make sure we’re taking every precaution to protect our patients and coworkers. Currently, the EPA reports that COVID-19 is not present in municipal water systems, but in light of the pandemic, it’s even more critical that dental offices become diligent in our maintenance of DUWLs. Our knowledge and education on COVID-19 is continually evolving and there is still much we don’t know about the transmission and virulence. Until there’s more information offices should be extra cautious.


1. Bankaitis AU. HIV/AIDS overview: Catalyst for change in infection control. AudiologyOnline. April 25, 2016. Accessed June 3, 2020. https://www.audiologyonline.com/articles/hiv-aids-overview-catalyst-for-16913
2. Chandler J. How to maintain dental unit waterlines. Dental Products Report. January 20, 2019. Accessed May 25, 2020. http://www.dentalproductsreport.com/dental/article/maintaining-dental-unit-waterlines?page=0,2 
3. Garland K. How can dental offices prevent Legionnaire’s disease? Dimensions of Dental Hygiene. April 24, 2020. Accessed May 24, 2020. http://www.dimensionsofdentalhygiene.com/article/how-can-dental-offices-prevent-legionnaires-disease 
4. Dental Unit Waterlines. US Food and Drug Administration. Updated September 4, 2018. https://www.fda.gov/medical-devices/dental-devices/dental-unit-waterlines
5. Dental unit waterlines. Key points. American Dental Association. Updated March 20, 2019. Accessed May 23, 2020. http://www.ada.org/member-center/oral-health-topics/dental-unit-waterlines
6. Requirements for maintaining dental water lines. California Dental Association. February 16, 2017. Accessed May 16, 2020. http://www.cda.org/home/news-and-events/Newsroom/requirements-for-maintaining-dental-water-lines 
7. Dental unit water quality. Centers for Disease Control and Prevention. June 18, 2018. https://www.cdc.gov/oralhealth/infectioncontrol/summary-infection-prevention-practices/dental-unit-water-quality.html

MELISSA VAN WITZENBURG, MS, RDH, has been practicing dental hygiene for 17 years. She continues to pursue her passion by assisting in the creation of an oral health initiative to educate the aging population about oral health and systemic links. Van Witzenburg also works clinically in a periodontal office in the Chicagoland area. For more information email her at [email protected].