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Water Safety: Three essential steps to ensuring your dental waterlines are bacteria-free.

As a dental assistant, you are not just the glue of the office, you're the protector. Often, you shoulder most of the infection control responsibilities. Doctors, hygienists, and especially patients rely on you to make sure each visit is as safe as possible. One of those areas you're called on to protect is in dental unit waterlines.

Since 2015, there have been nearly 100 confirmed cases of infection linked directly to dental waterline contamination. Most notably was the outbreak in Anaheim, California, where 72 healthy children, ages 2-12, were infected with mycobacterium abscessus, a similar bacteria to those causing tuberculosis and leprosy. Children lost permanent teeth, were prescribed heavy doses of antibiotics, and many required surgery to remove parts of their jaw. Multiple practices were permanently closed, lawsuits were filed, and long-built reputations were ruined. The aftermath received national news coverage, including on CNN, NPR, and Good Morning America.

The problem wasn't that the offices involved in these situations didn't care, but that they didn't know the science.

Dental waterlines don't just contain bacteria, they're the perfect environment for its growth. The narrow plastic tubing of waterlines contains billions of microscopic bores on its surface area, which helps bacteria attach, bundle, and mature (R-Tech Dental). Its slow flow rate and long periods of stagnation make the environment more characteristic of a pond collecting scum than a river filled with fresh water rapids.

When water does flow, i.e., when an instrument like the air-water syringe is engaged, water with new bacteria reinforcements enters and stagnant water moves a few inches down the line to carry bacteria to spread and multiply.

Put simply, bacteria never quits. That means treating dental unit waterlines is never done either.

It's a battle you can win, however, and patients count on it. To win, follow the three necessary aspects of every effective dental waterline maintenance protocol.

1. Shock Your Waterlines

Research shows that every waterline maintenance protocol needs an effective shocking component to consistently exceed the guideline set by the Centers for Disease Control (CDC) for safe water: less than or equal to 500 CFU/mL. And the reason for this goes back to the science.

To "shock" your waterlines means to run a high-level disinfectant (such as bleach, hydrogen peroxide, or large amounts of chlorine, silver, etc.) through your waterlines. These powerful antimicrobial agents are able to kill and/or remove bacteria from your waterlines completely so that you can start from zero. However, because these disinfectants are potent disinfectants, they're unsafe for patient contact. They must be used only at weekly or monthly intervals and must be completely removed from the lines before treating patients.

Consider the following three recommendations for when to shock your waterlines:

* Shock before first beginning a treatment protocol or when changing treatment products (i.e., before you start using a new box of tablets or installing a new straw).

* At least every quarter (90 days).

* When your waterline test reveals a contamination level of 200 CFU/mL or more.

How to shock depends on the product you chose. Always check with your dental unit manufacturer first, but there are a few dental-specific shock products available or a 1:13 diluted bleach solution has also been accepted if left in waterlines for no longer than 10 minutes.

2. Use a Proven Continuous Waterline Treatment

While shocking your waterlines effectively clears them of bacteria, studies show that without relying on a proven treatment solution to maintain that purity, biofilm can regrow inside your waterlines to 400 times the 500 CFU/mL standard in just four days. (1) That is why a continuous treatment product is recommended.

A continuous, or daily, treatment product is one that is continuously inside the lines to fight incoming bacteria. These products contain low-level antimicrobials that maintain clean lines while also being safe for use during patient treatment.
Pass/Fail Rates by Product Type

                           Pass Rate  Failure Rate

Tablets w/ Separate Shock     88%          12%
Tablets                       77%          23%
Straws/Cartridgets            72%          28%
Shock Treatments              60%          40%
Central Systems               58%          42%
Daily Liguids                 58%          42%

Note: Table made from bar graph.

A variety of products are available, but not every product proves effective in real-world practices. Researchers John A. Molinari, PhD, and Nancy Dewhirst, RDH, found that on average, 31 percent of treated dental waterlines fail to meet the CDC's standard for safe water. Some fail considerably more. While each treatment type can be effective, Molinari and Dewhirst concluded that "The data show that periodic shocking combined with daily antimicrobial treatment yielded the highest pass rate (88%) and appears to be the most reliable long-term protocol." (2)

3. Regularly Test for Assurance

Because every treatment type can fail, it's important that your office regularly test its waterlines as recommended by the CDC, American Dental Association (ADA), and Organization for Safety, Asepsis, and Prevention (OSAP). This is the only method to ensure your treatment protocol is actually delivering safer water to patients.

To test, your office has two options: mail-in water test services and in-office waterline tests.

In-office waterline tests are designed to be a little more economical and time-saving. They are great for giving a practice a baseline for the current safety status of each waterline. However, these tests have been found to be less reliable than laboratory testing. They may not have the neutralization methods necessary for accurate results and are prone to errors. Many industry leaders recommend that in-office waterline tests should be used in conjunction with validated laboratory testing (mail-in).

Via your office's product supply company you can purchase mail-in dental waterline testing kits from laboratories. Labs send your office a complete waterline kit with everything necessary to take samples, keep them viable, and return ship overnight.

Usually, laboratory testing uses advanced technology, trained specialists, and scientific methods to ensure accurate results. They also provide independent safety reports that can be assets if an office is inspected by regulatory agencies or if patients ever ask questions.

While testing should be conducted regularly, there are two rules of thought about what "regular" means. One is that dental offices should follow the dental treatment product manufacturer's recommendations, but this can range from monthly to, shockingly, never. OSAP, an advocacy organization for oral healthcare safety and infection-free treatment, recommends testing monthly until passing results are consistent for three consecutive months and then quarterly.

Ultimately, waterline maintenance comes down to a dedication to patient safety. It's no one's favorite thing. But when a patient sits in your chair, he or she is trusting dental professionals to practice with great knowledge, skill, and care.

We encourage your office to treat thoroughly and test regularly. Do your research and understand the risks. When you do, you'll be living up to the call to protect your patients and practice. 7)

Works Cited

(1.) Barbeau, J., Tanguay, R., Faucher, E., Avezard, C., Trudel, L., Cote, L., & Prevost, A. (1996). Multiparametric analysis of waterline contamination in dental units. Appl Environ Microbiol, 62(11). Retrieved from

(2.) Dewhirst, Nancy, and John A Molinari. Current Topics in Infection Control: Treating and Monitoring Dental Water. Compendium, 2018,

By Kelley Birschbach

Kelley Birschbach is waterline safety specialist with ProEdge Dental Water Labs in Centennial, CO. Reach her at For more information, visit
Why does bacteria grow so well in DUWLs?

Dental Unit Waterlines                  Tap Water Lines

Small Diameter (1/16" - 1/8")           1/2" Diameter
Very slow rate drips/second             5L/minute flowrate (>1000x
Plastic tubing is hydrophobic making    Copper as a metal and as a
biofilm attachment easy                 dissociated ion is
The tubing is also a source of carbon   Small surface area to water
(food) for bacteria                     volume ration
Large surface area to volume ratio      Smooth interior
Left stagnant for long periods of time  Fresh every time turned on
Chlorine rapidly dissipates over 24     Chlorinated and replenished with
hours and can even be absorbed by       every use

- Michael Wiltrout, Owner of R-Tech Dental of MN, LLC
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Author:Birschbach, Kelley
Publication:The Dental Assistant
Geographic Code:1USA
Date:Nov 1, 2018
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