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Optimal Dental-Unit Water-Line Care: Reducing the Risks

Patti DiGangi, RDH, BS

April 2024 RN - Expires Monday, November 30th, 2026

Inside Dental Assisting


Dental-unit water lines (DUWLs) can be a breeding ground for infection-causing biofilm, so cleaning, maintaining, and monitoring equipment used during dental procedures is imperative. This article explains the problem of contaminated DUWLs and describes infection control measures. Testing protocol is outlined and specific treatments are depicted.    

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Dental-unit water lines (DUWLs) are used daily in dental practices. The importance of proper infection control to maintain the safety of both patients and healthcare professionals is apparent because DUWLs are a breeding ground for infection-causing biofilm. During routine procedures, dental healthcare professionals, especially dental hygienists, are exposed to tens of thousands of bacteria per cubic meter, some of which is airborne. Research shows that microbial counts can reach 200,000 colony-forming units (CFUs) within 5 days of installing a dental water line, or 400 times the preferred level.1 CFUs are clumps of cells that will form distinct colonies when left untreated, especially in stagnant water (Figure 1).

Although flushing DUWLs was once recognized as an efficient way to control microbial presence and decrease the planktonic bacteria in water, there are other strategies to control the presence of biofilm.2 Inside the tubing, water flows in a laminar fashion, meaning in parallel layers with no disruption in those layers. As a result, biofilm adheres to the sides of the narrow dental water line tubing and remains relatively stagnant, allowing continued growth. Biofilm can multiply rapidly and grow in an established, well-protected shell without treatment, so healthcare professionals must use effective methods to maintain water lines for the safety of themselves and their patients.3

Contaminated DUWLs

Biofilm can colonize within DUWLs and pose health risks, especially in elderly, immunocompromised, and/or immunosuppressed patients.4 Although most healthy individuals can fight off potential infection from biofilm, some patients cannot, so it is necessary to treat all patients as if they are immunocompromised to protect them all.

The microorganisms that colonize in DUWLs can include bacteria, fungi, and protozoans, including Legionella, Pseudomonas aeruginosa, Candida albicans, and nontuberculous mycobacteria (NTM), and can increase in number to cause illness and infection.5-7Some symptoms of exposure to these microorganisms, such as NTM, include fever, hemoptysis, cough, weight loss, appetite loss, fatigue, and night sweats.8

Legionella causes legionnaires' disease, which is a severe form of pneumonia or lung inflammation caused by infection that most people contract by inhaling the bacteria.9

P. aeruginosa can cause different types of infection in both immunocompromised and healthy people. Immunocompromised patients may experience infections of the blood, pneumonia, or infections after surgery, which can lead to severe illness and death; otherwise healthy patients can develop mild illness such as ear infections and skin rashes.10

C. albicans can cause a fungal infection from yeast. Oropharyngeal candidiasis, or thrush, is contracted when this infection develops in the mouth or throat. Invasive candidiasis can also enter the bloodstream and cause more severe infections throughout the body.11

Staphylococcus and Streptococcus are two very common bacteria that cause a multitude of infections. Staphylococcus can cause minor infections from skin problems such as boils and impetigo to more serious, life-threatening diseases, such as endocarditis, which is an infection of the inner lining of the heart, or septicemia (blood poisoning). Streptococcus can spread through coughs or sneezes because it is airborne, causing skin, blood, sinus, ear, and tonsil infections. If strep throat is left untreated, it can lead to more severe complications, such as kidney inflammation or rheumatic fever.12

Most organisms found in DUWLs occur naturally in aquatic environments, and water in these units colonized with gram-negative heterotrophic biofilm has high levels of lipopolysaccharide (LPS) that can trigger asthma in patients and healthcare professionals, skin rashes, gastrointestinal concerns, and delayed wound healing.13-17

To prevent contamination and health risk, water lines must be properly maintained.

Infection Control

DUWL water quality must be maintained by first consulting with the manufacturer for appropriate methods and equipment to perform maintenance protocols.

The Centers for Disease Control and Prevention (CDC) recommendation is that the water used during nonsurgical dental procedures meet the Environmental Protection Agency (EPA) regulatory limit for drinking water, or ≤500 CFU/mL of heterotrophic water bacteria. Exposing patients and healthcare personnel to water of unknown biological quality is inconsistent with accepted general principles and puts them at risk.7

For surgical procedures, sterile saline or sterile water should be used through an appropriate delivery device that does not include a DUWL because the lines cannot be guaranteed sterile for surgical procedures. Appropriate delivery devices include bulb syringes; sterile, single-use disposable devices; or sterile water delivery systems that use sterile single-use disposable or sterilizable tubing.7

In addition to using the proper water with correct CFU levels, DUWL systems must be treated and monitored according to the manufacturer's instructions. Using filtration, chemical treatments, and anti-retraction valves on DUWLs will help improve the water quality, but it will not completely eliminate biofilm. Filters need to be changed depending on the level of biofilm measured when monitoring the water output. It can also be helpful to use water reservoir systems that are separate from the public water system, if possible. This will help deter any potential issues when a public water supply is compromised.18

Microorganisms can also be introduced through patients' mouths during treatment. To help facilitate a safer environment and reduce risk due to this exposure in the water lines:

• Install anti-retraction valves.19
• Flush DUWLs for several minutes every morning and every evening and expel the water out of the handpiece lines and every appropriate handpiece every morning.19
• Flush DUWLs for ≥20 seconds between patients to reduce exposure.19
• Never use warm water in the DUWL, even for the patient's comfort, because it can increase biofilm growth.5,19

After an established protocol is in place, it is important to educate the entire dental-practice staff on how to follow this protocol for DUWL maintenance, including regularly monitoring the methods used to treat the water quality and clean the lines, updating the methods as needed.18

Testing Protocols

Cleaning and maintaining DUWLs is the first step to keeping patients and healthcare professionals safe, using an established protocol and schedule. It is also important to remember that this process is a team effort by educating the entire office staff on these procedures. To ensure the established methods of DUWL maintenance are effective, the water that comes from the unit must be tested.18 The practice of testing DUWL water has always been recommended by the CDC, but some states may soon make it a requirement; some DUWL manufacturers recommend a schedule for monitoring their equipment.18There is a three-step process for DUWL testing:

1. test
2. shock
3. maintain

In the test step, either an in-office screening test or a test laboratory through a mail-in service should be used. The laboratory test will be most reliable.20 A sample of the water from the DUWL is poured into a solid medium and spread evenly over the surface. The plate is then incubated until bacterial colonies form on the surface of the medium (Figure 2).

The shock step is necessary when the result of the water quality test yields a result >500 CFU/mL. The shock treatment is designed to completely dislodge any established biofilm for the length of the entire unit water line. Several chemical shock treatments are available, including chlorhexidine gluconate 0.12%, sodium hypochlorite, chlorine dioxide, and hydrogen peroxide. Studies show that residual shock chemicals are present in posttreatment water lines, which is important to consider for patient and environmental exposure.21 Any chemical treatment chosen must be approved by the US Food and Drug Administration (FDA) and EPA to be considered safe for patients and the environment.

Chlorhexidine Gluconate 0.12%

Chlorhexidine gluconate 0.12% is often used for irrigation and has been shown to be efficacious against a broad spectrum of bacteria as well as Candida, which is a fungus. It is FDA-approved, environmentally friendly, time-efficient, and can be used to shock and maintain.21

Sodium Hypochlorite and Chlorine Dioxide

Both sodium hypochlorite and chlorine dioxide have advantages and disadvantages. Although they are inexpensive and bactericidal, they are harsh, inefficient, not sustainable, and unfortunately can contribute to a dangerous chemical formulation when combined with biofilm. Bleach and biofilm can create chloroform, which can daze or cause patients to pass out even in small doses. Sodium hypochlorite can be irritating to the eyes, skin, and respiratory system, and can be corrosive on equipment. Chlorine dioxide is not as corrosive, but the time needed for it to be effective is 2 hours, which is not time-efficient.22

Hydrogen Peroxide

Hydrogen peroxide is most effective when it oxidizes. In a study comparing several different concentrations, it was shown to be effective in maintaining an acceptable level of CFUs in biofilm-free tubing.23When biofilm is present, up to 2 months of continuous line treatment must take place until acceptable CFUs are achieved. Hydrogen peroxide is the most common choice for water bottle treatments, but it has some additives that must be considered, especially depending on a patient's immune state.

When biofilm is completely removed, it is safe to proceed with the maintenance step. The goal is to prevent or slow new adherence of biofilm within the water lines by using the manufacturer-recommended maintenance guidelines for a specific unit. It is helpful to select a dedicated maintenance manager to ensure maintenance is performed on a regular schedule.

The Job Is Never "Done"

Healthcare professionals know that the safety of patients and staff are of utmost importance. The responsibility of cleaning, maintaining, and monitoring equipment used during dental procedures, both surgical and nonsurgical, ultimately falls on the dentist. To ensure there is less risk of infection and spread of disease, a cleaning and maintenance protocol should be put in place and monitored on a regular basis. Adjustments that are deemed necessary should be made. The dentist and staff must be educated about the dangers of CFUs and biofilm in water lines and on best practices for maintaining clean, high-quality water.


1.The importance of dental unit waterline maintenance-infection control. OSHA Review Blog. Published February 22, 2017. Accessed June 17, 2019.

2. Rice EW, Rich WK, Johnson CH, Lye DJ. The role of flushing dental water lines for the removal of microbial contaminants. Public Health Rep. 2006;121(3):270-274.

3. Dental unit waterlines: questions and answers. Organization for Safety, Asepsis and Prevention. Accessed June 17, 2019.

4.Ricci ML, Fontana S, Pinci F, et al. Pneumonia associated with a dental unit waterline. Lancet. 2012;379(9816):684.

5. Kohn WG, Collins AS, Cleveland JL, et al; Centers for Disease Control and Prevention. Guidelines for infection control in dental health-care settings-2003. MMWR Recomm Rep. 2003;52(RR-17):1-61.

6. Peralta G, Tobin-D'Angelo M, Parham A, et al. Notes from the field: mycobacterium abscessus infections among patients of a pediatric dentistry practice--Georgia, 2015. MMWR Morb Mortal Wkly Rep. 2016;65(13):355-356.

7. Dental unit water quality. Centers for Disease Control and Prevention.

8.Molinari JA. Dental water line infection control: a work in progress. Dental Economics. Published February 8, 2017. Accessed June 17, 2019.

9. Legionnaires' disease. Mayo Clinic. Accessed April 22, 2019.

10. Pseudomonas aeruginosa in healthcare settings. Centers for Disease Control and Prevention. Accessed April 22, 2019.

11. Candidiasis. Centers for Disease Control and Prevention. Accessed April 22, 2019.

12. Strep throat. Mayo Clinic. Accessed April 22, 2019.

13. Huntington MK, Williams JF, Mackenzie CD. Endotoxin contamination in the dental surgery. J Med Microbiol. 2007;56(pt 9):1230-1234.

14. Puttaiah R. Assessment of endotoxin levels in dental effluent water. J Dent Res.1998;77(AADR Abstracts):262.9.

15. Szymańska J. Exposure to bacterial endotoxin during conservative dental treatment. Ann Agric Environ Med. 2005;12(1):137-139.

16. Pankhurst CL, Coulter W, Philpott-Howard JN, et al. Evaluation of the potential risk of occupational asthma in dentists exposed to contaminated dental unit waterlines. Prim Dent Care.2005;12(2):53-59.

17. Mills SE, Porteous N, Zawada J. Dental unit water quality: organization for safety, asepsis and prevention white paper and recommendations-2018. Accessed April 22, 2019.

18. Dental unit waterlines. American Dental Association. Accessed April 22, 2019.

19. Dental unit waterlines: dental unit water line fact sheet. Organization for Safety Asepsis and Prevention. Accessed April 22, 2019.

20. Porteous N, Sun Y, Schoolfield J. Evaluation of 3 dental unit waterline contamination testing methods. Gen Dent. 2015;63(1):41-47.

21. Siebert K. Safe water delivery. RDH Magazine. Published November 12, 2013. Accessed June 17, 2019.

22.Smith AJ, Bagg J, Hood J. Use of chlorine dioxide to disinfect dental unit waterlines. J Hosp Infect. 2001;49(4):285-288.

23. Agahi RH, Hashemipour MA, Kalantari M, et al. Effect of 0.2% chlorhexidine on microbial and fungal contamination of dental unit waterlines. Dent Res J (Isfahan).2014;11(3):351-356.

Fig 1. This figure illustrates how rapid growth occurs due to the type of bacteria and fungi that become trapped in DUWL tubing.

Figure 1

Fig 2. Testing a water sample in a laboratory requires a few simple steps, as shown in the figure.

Figure 2

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SOURCE: Inside Dentistry | April 2024

Learning Objectives:

•      Discuss the CDC and EPA standards for dental-unit water-line systems.
•      Identify a process that fits the needs of a dental practice.
•      Create a water-line maintenance protocol that includes regular monitoring.

Author Qualifications:

Patti DiGangi, RDH, BS graduated from William Rainey Harper Dental Hygiene and received her Bachelor of Science degree in Health Care Leadership from National Louis University. She continues to take an active future-oriented leadership role in a variety of professional organizations. She is the Dental Corporate Chair for the Oral Cancer Foundation Walk for Awareness of Northern Illinois and has been speaking and writing on the early detection and prevention of oral cancer for many years.


The author reports no conflicts of interest associated with this work.

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