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Passing the dental unit waterline test: 4 steps you need to know

Oct. 14, 2022
Have you ever made any of your patients sick? How do you know for sure? Amanda Hill was surprised at what she was missing regarding dental unit waterline maintenance.

Remember how hard you worked to pass the hygiene boards? You jumped through the rigorous hoops to earn that coveted RDH after your name. What if I told you there was another test hygienists need to take, and if we fail that test, we could potentially harm patients, coworkers, and ourselves?

I had been a dental hygienist for 20 years before I heard anyone talk about testing dental unit waterlines. I was attending the annual required infection control continuing education, when the speaker started talking about testing waterlines to make sure they were safe. He told a story about children in California who required multiple surgeries from contaminated dental unit waterlines. Holy cow! Could I do that to someone?

I’m grateful that when I asked about our office’s waterline protocol and found we had none, no one got in my way. The doctor told me to do what I needed to do. I shocked and tested our lines. We failed miserably, and so began my waterline journey.

Why does this matter?

Think about your dental unit waterlines (DUWLs) and that tiny tubing. Because the tubes are so small, biofilm can quickly grow in them, and that biofilm can produce some virulent stuff that can harm not only patients but can end up in the aerosols we breathe.

One study revealed that dental professionals are more likely to have legionella antibodies because of contaminated DUWLs.1 Ongoing studies show that the aerosols in dental operatories are not coming from aerosolized saliva but from, you guessed it, DUWLs.2 This is excellent news! If we take care of our DUWLs, we don’t need to worry about what we’re breathing in our operatories.

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But before you say you’ve never made anyone sick, in the California case, of the 202 children affected, symptoms showed up between one and 409 days after exposure—409 days! As a clinician for more than 25 years, all I can say is, I don’t know if I’ve ever made anyone sick. But I can say for sure that I will do everything I can to never expose a patient (or myself and coworkers) again.

Thankfully, setting up a waterline protocol is easy and kind of fun. I look at it as a race against biofilm, and I’m determined to be faster! Here are the four steps (figure 1).

First you shock

If all this waterline stuff is news to you, the first step is to shock. Shocking uses a high concentrate antimicrobial to blast through and break up the biofilm that has taken up residence in the lines. There are many products with varying instructions. Some are fast, such as bleach, while others take three days of shocking, like Liquid Ultra. Pick one and follow the instructions.

You will also need to shock if you’re changing any of the products you use to take care of your waterlines. So, if your sales rep alerts you that a different product is on sale, just know there are steps to take before switching. Shocking clears the lines, and every product leaves a residue. When you introduce a new product without cleaning the old one, you’re playing chemistry in your lines. Your patients might notice a strange taste, or there might be some funny smells. Shocking provides a blank slate for your biofilm battle.

Then you treat

Once you’ve gotten that biofilm under control, it’s essential to keep it that way. That’s where treatment products come in. Treatment products deliver a low level of antimicrobial through your lines between shocks. Some offices shock or treat, thinking one is enough. But it’s much like how we have patients come in for periodic hygiene visits so we can get into the pockets and disrupt that biofilm (shocking). Then we have them perform home care in between visits (treating). We would never have them do one without the other. Your DUWLs also need both.

Like shock products, there are quite a few treatment products on the market. There are tablets that dissolve into your treatment water each time you fill up your bottle, straws to place in your unit water bottle to deliver the treatment automatically, and liquids that have a variety of different instructions for use (IFU). They all keep the biofilm from building.

Then it’s time to test

Next, test to learn whether your shocking and treating are doing the job. Passing the test means your water has less than 500 colony-forming units (CFUs); that’s the standard set by the Environmental Protection Agency (EPA) for safe drinking water.3 However, if your test reveals even 200 CFUs, I’d consider that a fail and go back to shocking. That’s because 200 CFUs can quickly become 400 CFUs and then 800 CFUs and so on. You must get ahead of the growth.

Waterline tests can be in-office or mail-in. Make sure that the test you’re using is for dental unit waterlines. I’m a huge fan of the QuickPass by ProEdge. Not only can I get my results in 48 to 72 hours, but it’s also confidential and convenient. The Organization for Safety, Asepsis and Prevention (OSAP) recommends testing monthly until you have two consecutive passes; then you can test quarterly. Dental unit manufacturers are getting on board and recommending testing as well. We do mail-in testing for third-party verification once a year in our office; then we use in-office tests.

Now it’s time to maintain

Now you need a system to keep your lines safe. This involves daily maintenance, regular testing, and periodic shocking. Your tests will let you know when to shock, but in the beginning, you will likely have to do it monthly. Then you can move to quarterly, and then as needed. Keep a log of all your efforts, not only to stay on track, but if you’re ever inspected, this is sure to be on the checklist. Some companies, such as ProEdge Dental Water Labs, have a digital dashboard to keep track of all your mail-in tests, or a downloadable PDF you can print and fill out.

Remember the kids in California? The case is due to go to trial in 2022. Edwin J. Zinman, DDS, JD, a lawyer in the case said, “The wheels of justice move slowly at times. It may be a few more months before a public announcement about any settlement can be made.” But it will hit the news cycle at some point and our patients will hear about it. How awesome would it be if your office could confidently tell patients that you treat and test your water? In fact, let them know now what you’re doing to keep them safe!

Through trial and error, I’ve gotten pretty good at this, and I find a lot of satisfaction when we pass the test. When we fail (one-third of all offices that test will fail,4), putting on my detective cap and figuring it out feels powerful. The best thing I’ve learned is the people at ProEdge Dental Water Labs are the Sherlock Holmes of waterlines and will dig in and help you pass no matter what product you use or how badly you fail.

Editor's note: This article appeared in the October 2022 print edition of RDH magazine. Dental hygienists in North America are eligible for a complimentary print subscription. Sign up here.


  1. Hamilton KA, Kuppravalli A, Heida A, Joshi S, Haas CN, Verhougstraete M, Gerrity D. Legionnaires' disease in dental offices: quantifying aerosol risks to dental workers and patients. J Occup Environ Hyg. 2021;18(8):378-393. doi:10.1080/15459624.2021.1939878. Epub; August 2, 2021. PMID: 34161202.
  2. 2.    Meethil AP, Saraswat S, Chaudhary PP, Dabdoub SM, Kumar PS. Sources of SARS-CoV-2 and other microorganisms in dental aerosols. J Dent Res. May 12, 2021. https://doi.org/10.1177/00220345211015948
  3. Dental unit water quality. Centers for Disease Control. Page last reviewed June 18, 2018. Accessed July 10, 2022. https://www.cdc.gov/oralhealth/infectioncontrol/summary-infection-prevention-practices/dental-unit-water-quality.html
  4. Molinari JA, Dewhirst N. Treating and monitoring dental water quality. May 2018. Compend Contin Educ Dent. May 2018.