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The Quality of Dental Unit Waterlines


Despite the seriousness of the coronavirus disease 2019 (COVID-19), dental healthcare professionals should not overlook waterline treatment or quality.

© Marko Rupena/Adobe Stock

© Marko Rupena/Adobe Stock

The aphorism, “Out of sight, out of mind” is appropriate when one talks about tidying up an area. It is not appropriate, however, when infection control is concerned. That is, just because something can’t be seen doesn't mean that a threat doesn't exist. That is certainly the case regarding dental unit waterlines (DUWL).

Coronavirus disease 2019 (COVID-19) has been the focus of infection control efforts and has occupied the time and minds of dental health professionals throughout the year, justifiably so. However, fear of COVID-19 transmission does not mean staff should overlook other areas of infection control.


The threats posed by contaminated DUWL are very real. They have led to several high-profile cases, including fatalities.

“There have been cases of disease transmission from the DUWL,” says Karen Daw, “The OSHA Lady” and a speaker and consultant. “In Italy, an elderly patient contracted legionellosis and died a few days later, and in cases on opposite ends of our country, outbreaks of M. abscessus infections occurred and the source is believed to be dental water.”

The dangers of contaminated DUWLs are nothing new and there has been formal, established guidance for years on mitigating contamination, says Mary Bartlett, President of SafeLink Consulting.

“The Centers for Disease Control and Prevention [CDC] has addressed waterline safety in dental units for quite some time,” Bartlett says. “In the 2003 MMWR Guidelines for Infection Control in Dental Health-Care Settings, the CDC recognizes that the plastic tubing that carries water to the high-speed handpiece, air/water syringe, and ultrasonic scaler can become colonized with microorganisms. In 1993 the CDC recommended that dental waterlines be flushed at certain intervals, however, studies show that this does not affect biofilm in the waterlines.”


The dental industry had a renewed focus on mitigating aerosol transmission of COVID-19 during aerosol-generating procedures (AGP), according to Daw. This was due to more public knowledge of how COVID-19 spreads through the air via water droplets and what aerosols patients may be exposed to at their dentist’s office, she adds. Part of these enhanced measures are laid out in the CDC’s Interim Infection Prevention & Control in Dental Settings 2019 guide, which also offers guidance on treating dental water units that had been sitting for a long time during the shutdown, Daw explains. However, it’s still necessary to balance those concerns with the infection control measures that previously existed.

“Hopefully the practice has been actively educating patients on all the steps the dental practice has been taking since reopening,” Daw says. “With the term ‘aerosol’ ubiquitous in the news and literature because of SARS-CoV-2, they may well question whether aerosols are generated in the practice, and if so, whether it’s safe. Team members should also have reassurances that the water they are being exposed to is safe. If a dental employee is exposed to, and later contracts an illness traced back to the exposure of harmful water, then [the Occupational Safety and Health Administration] OSHA may get involved because employee safety has been compromised.”

While DUWL issues are not exacerbated by coronavirus disease 2019, the pandemic (and its effect on dental practices) should cause practices to be a little more vigilant. As most practices across the country were closed for several weeks in the spring, water was sitting in the lines for a prolonged period of time, Daw explains. After consulting with the CDC’s guidance for reopening, practices should have consulted the manufacturer’s instructions for use (IFU) on how to treat waterlines after a prolonged period of non-use, she continues.

“The goal was to ensure the waterlines met the standards for safe drinking water, typically viewed as no more than 500 colony forming units of heterotrophic bacteria per milliliter,” Daw says. “This is the number established by the Environmental Protection Agency [EPA] as the upper threshold for safe drinking water. It’s important to note that only sterile water should be used for surgical procedures...Then, once meeting this goal, testing routinely to ensure the water remains safe.”

Unfortunately, these guidelines are not consistent across the country, but rather they vary state-by-state, according to Bartlett. An example of this is the State Board of Maryland, which does not require adherence with CDC guidelines, she says, adding that Safelink performs waterline testing in all of the practices it works with at least annually.


DUWL maintenance and treatment is prescribed by each system’s manufacturer. The CDC recommends consulting with the manufacturer to determine the best method for maintaining water quality, which is usually < 500 CFU/mL, Bartlett says.

This also includes the frequency of monitoring the quality of water,” she adds.

Maintenance and treatment can be similar across-the-board, and it’s common in dental practices to see water treatment with the use of water bottles installed on the dental units, Bartlett explains. It’s important for staff to read the instructions to determine if tap or distilled water is required for the specific product in use, she continues.

“Most dental units have a switch to engage either city water or bottled water,” Bartlett says. “Staff need to pay close attention to ensure that if bottled water is intended for use that the switch is in the correct position. Believe it or not, this can happen. This error can mean that the city water is not being treated to help eliminate the biofilm.”

Once the biofilm issue is addressed, there are several methods to maintain water quality, including tablets, cartridges or straws, liquids, and entire office filtration systems. Two of the most common treatment methods are straws and tablets. Straws are more robust and last longer, but are typically more expensive than their tablet counterpart, Bartlett explains.

“However, [a straw] provides an initial shock treatment when installed and then may not need to be changed for a year,” she says. “This can save staff time. Staff needs to follow the manufacturer’s instructions regarding the use of tap water or distilled water with the straw.”


Straws and tablets alone are not enough to maintain water quality. A process called shocking is also required and there are a number of products that can be used for this purpose, Bartlett says. However, there may be restrictions on which shocking product can be used with the practice’s water unit, so it’s important to contact the manufacturer to be sure, she adds.

“For instance, a mixture of sodium hypochlorite and water can be used on some dental units, but not all,” Bartlett says. “The last thing you want to do is corrode your equipment, so make sure you check with the manufacturer before using a bleach solution.”

When using a bleach solution, the ratio of water to bleach will vary based on the strength of the sodium hypochlorite, and it’s best to work with a reputable waterline testing company in these instances, Bartlett continues.

In her experience, Bartlett says that she’s found shocking products that have color, which provides a visual indication that all of the tubing contains shock treatment.

“The length of time that the shock solution remains in the tubing depends on the product used, so follow the manufacturer’s instructions,” she continues. “Retain the original tubing that goes from the unit into the bottle because if a straw is being used and shocking is to be performed, then the straw must be removed, and the original tubing used for the shocking procedure. In most practices, I see monthly shocking being performed. A set schedule should be established and documented to ensure that it is being performed.”


Regular treatment and shocking are necessary, but still need to be supplemented by routine testing to ensure its success. There is no one-size-fits-all solution for waterline testing and the practice can perform these tests in-house or send the tests to a third-party, according to Daw.

“As far as the frequency of waterline testing, there are various methods from self-testing to lab testing,” Daw says. “The CDC doesn’t state the frequency in their guidelines, so consult with the manufacturer of the unit. This can also be a state requirement, so each dental practice should check their state board and other state requirements to ensure they are adhering to the guidelines.”

It's important to consult the unit’s manufacturer on the frequency of waterline testing, Daw advises. The consequence could be testing that is not performed frequently enough.

“For example, one practice after training said they had safe waterlines, that their dental equipment maintenance representative tests their lines every year,” she says. “At first, I was ecstatic until I read the IFU for the product they were using, and it recommended a much greater frequency. On top of that, when I asked for the test results, they could not provide any. Turns out, the testing was for TDS, or Total Dissolved Solids, not for pathogenic microorganisms.”

Practices should be testing for disease-causing microorganisms, such as Legionella, Pseudomonas aeruginosa, and nontuberculous Mycobacterium, Daw says. Microorganisms can be harmful in large numbers and can lead to biofilm. What’s more, these microorganisms can travel from the water supply as well as from the patients’ mouths, she adds.

While dental healthcare professionals have been concerned with the spread of COVID-19, the rudimentary aspects of infection control should not be neglected. The dental team should be trained on the shock products and maintaining and testing waterlines, Daw suggests. She also recommends that practices create a written standard operating procedure for waterline units and a log that ensures the frequency standards are being met, she advises. Staff should attend regular infection control and OSHA safety training, as well, Daw says. The Organization for Safety Asepsis and Prevention’s white paper, Dental Unit Water Quality: Organization for Safety, Asepsis and Prevention White Paper and Recommendations– 2018 is a good resource, she adds.

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