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Just Say No to Heated Waterlines

We have a new dental hygienist who said her previous office’s waterlines were heated. Wouldn’t this pose a bacteria risk?

Using heated water for dental unit waterlines (DUWLs) may enhance biofilm growth and proliferation, resulting in higher bacterial counts, which raises the risk of contamination during dental procedures.1 Biofilms thrive in warm environments, and the combination of moisture and warmth in heated water lines can lead to more rapid biofilm formation, potentially compromising water quality.1 Bacterial species, such as Pseudomonas, Legionella, and Mycobacteria, can be harmful or deadly to immunocompromised patients who are more susceptible to infections. In 2011, an otherwise healthy 82-year-old woman died from irreversible septic shock after acquiring Legionnaire disease from dental unit water used during treatment.2

Other problems with using heated water in DUWL include scale and mineral deposits that can narrow the diameter of the lines, impacting water flow and potentially affecting the performance of dental instruments. Heated water might also accelerate wear and tear on equipment reducing its lifespan and requiring more frequent maintenance. Heating water increases unnecessary energy consumption, raising expenses.

The 2016 United States Centers for Disease Control and Prevention Summary of Infection Prevention Practices in Dental Settings states, “All dental units should use systems that treat water to meet Environmental Protection Agency (EPA) drinking water standards (ie, ≤ 500 CFU/mL of heterotrophic water bacteria)” and recommends using water that meets EPA regulatory standards for routine dental treatment output water.3

Heterotrophic plate count (HPC) measures the number of waterborne bacteria in a sample. Additionally, the CDC issued an official health alert on October 31, 2022, emphasizing “the importance of following existing recommendations for maintaining and monitoring dental waterlines” after two major outbreaks of nontuberculosis Mycobacteria were discovered in large pediatric dental clinics in California and Georgia.4

To ensure safe water standards, all dental professionals should be educated about dental unit water quality, biofilm, water treatment, and dental unit maintenance including monitoring of water quality.3,5 Monitoring includes testing via chairside or laboratory to determine the HPC, which should be less than 500 CFU/mL. The Organization for Safety, Asepsis and Prevention (OSAP) white paper offers specific guidance on the frequency of monitoring or testing DUWLs.5

Mitigating DUWL problems begins with avoiding heated water. Following CDC and OSAP guidance by implementing proper maintenance and monitoring protocols ensures safe and effective DUWLs. Maintaining dental unit water quality is an essential part of routine infection control practices.


  1. Organization for Safety, Asepsis, and Prevention. What Is Biofilm? Available at: Accessed October 16, 2023.
  2. Ricci ML, Fontana S, Pinci F, et al. Pneumonia associated with a dental unit waterline. Lancet. 2012;379:684.
  3. United States Centers for Disease Control and Prevention. Summary of Infection Prevention Practices in Dental Settings. Available at: Accessed October 16, 2023.
  4. US Centers for Disease Control and Prevention. Outbreaks of Nontuberculosis Mycobacteria Infections Highlight Importance of Managing and Monitoring Dental Waterlines. Available at: Accessed October 16, 2023.
  5. Mills S, Porteous N, Zawada J. Dental unit water quality: organization for safety, asepsis and prevention white paper and recommendations– 2018. Journal of Dental Infection Control and Safety. 2018;1(1):1-27.

From Dimensions in Dental Hygiene. November/December 2023; 21(10):46

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