9 Things You Need to Know about Maintaining and Monitoring Dental Unit Waterlines

October 17, 2023

The Centers for Disease Control and Prevention (CDC) set the water quality standard for dental unit treatment water at ≤500CFU/ml of heterotrophic bacteria. Many dental practices are treating their dental unit water by placing a tablet or liquid in the water bottle or utilizing a valved cartridge (referred to as straws) in the water bottle to control the growth of biofilm and improve water quality. However, many practices assume that the product they use is working and that they are meeting the CDC’s water quality standard. The bottom line is that if you don’t test your dental unit water, you don’t know if you are meeting the standard. These are 9 things that you need to know about dental unit water quality.

1 - Patients can and have developed bacterial infections from contaminated dental unit water.

In 2015, 24 pediatric patients at a facility in Georgia developed Mycobacterium abcessus infections from exposure to contaminated water during pulpotomy procedures. In 2016, a similar outbreak occurred in California, involving 71 patients, who were hospitalized to treat the infections. More recently, the CDC issued a Health Alert through its Health Alert Network (HAN) emphasizing the importance of following recommendations for maintaining and monitoring dental unit water quality, based on past incidents and an ongoing investigation of yet another outbreak of infections. None of these outbreaks have resulted in patient deaths, however, 2 patients have died from Legionella infections contracted in dental practices from dental unit waterlines.

2 – Using distilled or filtered water in dental units does not prevent biofilm formation and water contamination.

Some dental professionals equate distilled water with sterile water – meaning that it has no microorganisms, that can contribute to the formation of biofilm in the dental unit waterlines. This is not true, however. Whatever type of water is used in the dental unit, something must be done or added to the water to maintain the safe water standard. There are a number of options that dental practices can implement to maintain safe water, including the addition of an antimicrobial tablet or solution each time the water bottle is filled, installing a valved cartridge or straw) into the water bottle, installing a whole-office or point-of-entry water purification system, in addition to utilizing municipal water connected to the dental unit or in a separate water reservoir/bottle. It is very important to consult the manufacturer’s instructions for the use of the equipment to determine the recommended method of treating the water in the dental unit. Waterline disinfectants/maintenance products act to inhibit the growth of bacteria and biofilm formation but do not prevent it.

3 - Surgical procedures require the use of sterile water or sterile saline for irrigation.

Due to the risk of introducing microorganisms into a sterile body cavity during surgical procedures, water from the dental unit should not be used to irrigate surgical sites. Sterile water or sterile saline can be dispensed from a sterilized bulb syringe or through the use of a specifically designed sterile water delivery system, that can be sterilized after each use. Placing sterile water or sterile saline into the dental unit water bottle does not ensure that the water is sterile when it exits the dental unit since it is exposed to the biofilm present in the dental unit waterlines.

4 – Most waterline maintenance products require a periodic shock treatment of the waterlines.

The manufacturers of dental unit waterline disinfectants/maintenance products have recommendations for a shock or cleaning treatment for the waterlines. The manufacturer of the disinfectant determines how often the shock treatment should be performed which may vary depending on the product used. Shocking involves adding an antimicrobial solution, usually at a higher concentration than the maintenance product, and leaving it in the lines overnight. This procedure will clean the lines and remove biofilm. Some products require three consecutive treatments to clean and remove all of the biofilm that has accumulated. Always follow the manufacturer’s instructions for the use of both waterline disinfectants and shock products – as they are not interchangeable.

5 – If you don’t test your dental unit water, you don’t know if you meet the safe water standard.

Although the products used in dentistry to treat and shock the dental unit waterlines have been tested for efficacy, there are many variables that can affect whether the product is working effectively in each dental unit. The only way to assess that the water meets the ≤500CFU/ml standard is to test the water in each unit. Testing the water can be done in-office or mailed to a water laboratory. The CDC states that testing should be performed “periodically”, however, most manufacturers recommend quarterly testing.

If the dental units in your facility have never been tested, a best practice would be to test all the units as a baseline. This can help identify any issues with specific units or individual waterlines. If any of the dental units do not meet the water quality standard, the lines in those units should be shocked and then retested. Be sure to record all test results for each dental unit.

6 – There are two ways to perform dental unit waterline tests.

The first method is to do a pooled test. This involves dispensing equal amounts of water from all the lines on a dental unit (air/water syringe, handpieces, and scalers) into the test container. The other is to test each waterline individually. Most practices use pooled samples. Testing individual lines is typically performed when the unit continually fails, and further determination is needed to find the source of the contamination. Always follow the manufacturer’s instructions for conducting the test.

7– Dental unit waterline tests are not meant to identify specific microorganisms in the water.

Dental unit waterline test kits are designed to determine the number of colony-forming units of bacteria in the water sample. In other words, does the water meet the standard or not. There are some water labs that will analyze the microbial content of the water, but it is usually not necessary for dental facilities unless a specific problem has been identified.

8 – Contaminated dental unit water is also a risk to the dental team.

While we tend to think of the risk to patients from exposure to contaminated dental unit water, the clinical team members are exposed to aerosols from that water (and saliva/blood from the patient) during most of the procedures that they perform each day. When dental handpieces, air-water syringes, and ultrasonic scalers are utilized, the aerosols created contain microorganisms that are contained in the biofilm in the lines. If the clinical team is not wearing appropriate personal protective equipment (PPE), they can also be exposed to potential transmission of infectious diseases from the dental unit waterlines.

9 – Dental practices should have written protocols for maintaining and testing their dental unit waterlines.

Consistency and accuracy are the keys to achieving safe dental treatment water for patients and team members. Written protocols, or standard operating procedures, help to ensure that each team member knows how to perform waterline maintenance procedures. Keep in mind that not all the dental units in a facility are the same, and different equipment may require slightly different protocols. As previously mentioned, the practice should also maintain documentation of waterline testing and shocking, in order to prove that the procedures have been done and make sure that no units have gone untested or untreated.

Dental unit water quality has been in the news a great deal over the past several years. Be proactive about your dental unit water quality by testing and following the recommended procedures for your equipment and the products that you use. Let your patients know that you do your utmost to provide them with safe care – including safe water.


CDC Morbidity and Mortality Weekly Report (MMWR), April 8, 2016, Notes from the Field: Mycobacterium abcessus Infections Among Patients of a Pediatric Dentistry Practice – Georgia 2015. https://www.cdc.gov/mmwr/volumes/65/wr/mm6513a5.htm  

CDC Health Alert Network (HAN) Outbreaks of Nontuberculous Mycobacteria Infections Highlight Importance of Maintaining and Monitoring Dental Waterlines https://emergency.cdc.gov/han/2022/han00478.asp  

CDC Healthcare Water Management Program Frequently Asked Questions https://www.cdc.gov/legionella/wmp/healthcare-facilities/healthcare-wmp-faq.html

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