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Cleaning and Maintaining Dental Unit Waterlines - Dentistry's Dirty Little Secret


Dental Unit Waterlines (DUWLs) began getting attention back in the late 1980s as infection control became a major focus for medical professionals. 

The first guideline for cleaning dental unit waterlines took hold in 1993 when the Center for Disease Control (CDC) officially recommended that dental waterlines be flushed daily to reduce microbial loads.

Dentistry's "Dirty Little Secret" Lies Inside Dental Unit Waterlines

But it was in 2000 that the public first became aware of dental unit waterline contamination. ABC’s television show 20/20 aired a special called “Dentistry’s Dirty Little Secret” exposing that many dental offices were putting water in their patients’ mouths that were several times more contaminated than toilet water. It was not a pretty picture.

And it’s still not. We know this is more than a clever comparison because recent results from a dental unit waterline test and from our warehouse bathroom prove things inside dental waterlines can be pretty polluted.

Waterline test results comparing our warehouse toilet with a recent hygiene school's waterline test results.

When in 2015 and 2016, there were a reported 96 children infected in two pediatric dentistry on the east and west coasts of the United States because of contaminated dental unit waterlines, more professionals began taking notice.

In fact, at the OSAP Dental Infection Boot Camp in 2017, infection control experts Shannon E. Mills, DDS, John A. Molinari, PhD, and others commented that it was the number 1 challenge facing dental professionals over the next 5 years.


There are options to solve this challenge, but first, let’s get down to the nitty gritty - the science of dental unit waterline contamination.


Dental Unit Waterlines: The Perfect Environment for Biofilm

As a dental professional, it might seem like the mouth is the perfect environment for microbial growth, but dental unit waterlines make for a great competitor. Not only do dental waterlines support growth, they also feed it.

Unlike the municipal waterlines leading to your office or your house, dental waterlines are made of a small-bore plastic tubing. These tubes material-makeup includes carbon, one of bacteria’s favorite foods, and the small-bore surface area helps bacteria attach, bundle, and mature.

Why does bacteria grow so well in dental unit waterlines? Small diameter; very slow flow rate; plastic tubing makes biofilm attachment easy; tubing is a source of carbon (food) for bacteria; larger surface area to volume ration, left stagnant for long periods of time; chlorine rapidly dissipates over 24 hours and can be absorbed by tubing.

Your municipal lines are made of copper, which as a dissociated ion is antimicrobial / bacteriostatic. Municipal lines are also as much as 8 times wider than dental unit waterlines making their surface area to volume ratio much smaller. The smaller surface area means bacteria is more likely to flow past rather than latch onto the waterline wall.

One of the other unique differences about dental waterlines is their slow flowrate. We often think of the small tube as creating a river-like flow, but it’s much more like a pond with a small drain. Municipal lines, for example, flow at 5L/minute. That’s over 1,000 times the rate of dental unit waterlines (R-Tech Dental of MN, LLC).

This flow rate, of course, is due to the inconsistent use of handpieces during and between patient visits. Over the course of a day, dental unit waterlines are likely to be inactive 23.5 hours every day. That’s a lot of stagnation.

When the air-water syringe or handpiece or cavitron is engaged, the slow flowrate helps small pieces of the biofilm to break from their colony, flow a few inches down the line to start the process over again or flow out of the end of the line and into the patient’s mouth.

Fingers and small pieces of biofilm detach from their colonies to spread in the direction of water flow inside dental unit waterlines. Copyright: 2003, Center for Biofilm Engineering at MSU-Bozeman

We like to say it like this: every time the air-water syringe is engaged, it’s like blowing on a dandelion, spreading the seeds down the line to develop roots, grow strong, and do it all over again. And biofilm may not look like much in the picture above, but their colonies are highly organized and efficiently multiply and spread. And while they build up reinforcements, new bacteria enters waterlines all the time.

Bacteria never quits.


Dental Unit Waterlines: How To Get Them Clean and Keep Them Clean

That means treating dental unit waterlines is never done either. But while it isn't easy in that way, it can be simple.

First - and like all infection control measures - it requires professionals dedicated to patient safety. And we know most dental practices are, but it can be tempting to shave efforts wherever possible. And we get it - it's tougher and tougher to run a practice with the increasing demands from outside regulators, internal dynamics, and the growing costs to practice. That's why it's our team's goal to help professionals and practices feeling that tension to continue giving their patients the absolute best economically and effectively.

So stay vigilant! You got this!

Next, cleaning your waterlines requires shocking them. Shocking your waterlines is the process of using a strong disinfecting agent to rid your lines of nearly all bacteria. This is the part of a comprehensive dental unit waterline maintenance protocol that allows continuous treatments like tablets, straws, cartridges, and liquid drops to work effectively.

Each treatment product is different and requires different shocking intervals, but after testing hundreds of thousands of dental unit waterlines with every product available, we know for sure that every treatment product can fail and that improper shocking is often the reason. Read your instructions carefully and follow the tips on our product selection guide to be most effective in your protocol.

Learn Your Shocking Options, When to Shock, and How to Shock Dental Unit Waterlines

After shocking, use a continuous dental water treatment. These treatments are designed to be continuously in your dental unit waterlines fighting bacteria. They are safe for your patients and your equipment, but maintain the clean lines your shocking protocol already established.

These continuous treatments include tablets, daily liquids, and cartridges or straws. Research products carefully to determine what will be most effective for your practice and make sure to follow instructions for use carefully. Sometimes things are sold one way and work another.

See How Different Dental Waterline Treatment Types Perform in Real-World Practices

Last, it is vital to regularly monitor your waterlines. Over 30% of all treated dental waterlines fail to meet the less than 500 CFU/mL (colony-forming units per milliliter) CDC guideline for safe water. Over 60% of dental practices have at least one failing waterline when they test.

It’s not because they aren’t working at it or do not care; it’s because no treatment product is perfect, and often, instructions for use could be much more clear.

The CDC recommends frequent testing. The American Dental Association maintains that testing the only way to ensure your treatment product is working and suggests monitoring your waterlines consistently. A-Dec recommends monthly monitoring until consistent passing results and then quarterly testing.

Our team recommends at least quarterly testing of your dental waterlines to ensure your patients and practice are safe.

Why, When, and How to Test Dental Unit Waterlines


Dental Unit Waterlines: They Don't Have to Be Your Dirty Little Secret

Sample ProEdge Waterline Safety Test ReportAs top dental professionals and industry experts continue helping dedicated dental professionals practice with the highest standard of care through effective dental unit waterline safety, it won't matter if "the secret" gets out because more and more waterlines will be clean. And their practice have the official report to prove it.

Will yours?


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Learn the 3 Steps to Safe Water:



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Additional Resources:

Dental Water Treatment Product Selection Guide

Three Necessary Aspects of Every Dental Waterline Treatment Protocol

How to Shock Your Waterlines

Dental Water Testing - A Comprehensive Guide

Calling All California Dental Pros to Higher Water Safety Standards - Assembly Bill 1277