Dental Unit Water Quality

Biofilm is a thin, slimy film of bacteria that sticks to moist surfaces, such as those inside dental unit waterlines. Biofilm occurs in dental unit waterlines because of the long, small-diameter tubing and low flow rates used in dentistry, the frequent periods of stagnation, and the potential for retraction of oral fluids. As a result, high numbers of common water bacteria can be found in untreated dental unit water systems. A few disease-causing microorganisms found in untreated dental unit water include Legionella, Pseudomonas aeruginosa, and nontuberculous Mycobacterium. Dental health care personnel and patients could be placed at risk of adverse health effects if water is not appropriately treated.

Dental health care personnel should use water that meets environmental protection agency regulatory standards for drinking water (i.e., ≤500 colony forming units (CFU)/mL of heterotrophic water bacteria) for non-surgical dental treatment output water. Consult with the dental unit manufacturer for appropriate methods and equipment to maintain the quality of dental water. Commercial devices and procedures designed for this purpose include:

  • Self-contained water systems (e.g., independent water reservoir) combined with chemical treatment (e.g., periodic or continuous chemical germicide treatment protocols).
  • Systems designed for single-chair or entire-practice waterlines that purify or treat incoming water to remove or inactivate microorganisms.
  • Combinations of these methods.

For surgical procedures, sterile saline or sterile water should be used as a coolant/irrigant. Conventional dental units cannot reliably deliver sterile water even when equipped with independent water reservoirs containing sterile water because the water-bearing pathway cannot be reliably sterilized. Appropriate delivery devices (e.g., bulb syringe; sterile, single-use disposable products; or sterile water delivery systems that bypass the dental unit by using sterile single-use disposable or sterilizable tubing) should be used to deliver sterile water during surgery.

Monitoring dental unit water quality can help identify problems in performance or compliance with maintenance protocols and also provides documentation. Follow recommendations for monitoring water quality provided by the manufacturer of the unit or waterline treatment product. Commercial self-contained test kits or water-testing laboratories are available for this purpose.

Yes, there have been documented cases of disease transmission from dental unit waterlines. In 2011, an 82-year-old woman in Italy was diagnosed with legionellosis and died 2 days later. The patient’s only known risk of exposure for Legionella infection were two dental appointments. Molecular testing was able to identify the dental unit waterlines as the source of the bacteria. Most recently, in 2015, an outbreak of Mycobacterium abscessus odontogenic infections was reported in children receiving pulpotomy treatment from a pediatric dental clinic. The suspected source of the Mycobacterium was contaminated water from dental unit waterlines.

A boil-water advisory is a public health announcement that the public should boil tap water before drinking it. During a boil-water advisory:

  • Do not deliver water from the public water system to the patient through any dental equipment that uses the public water system. This restriction does not apply if the water source is isolated from the municipal water system (e.g., a separate water reservoir or other water treatment device cleared for marketing by the Food and Drug Administration).
  • Have patients rinse with bottled or distilled water until the boil-water advisory has been cancelled.
  • Do not use tap water to dilute germicides or for hand hygiene unless the water has been brought to a rolling boil for >1 minute and cooled before use.
  • For hand hygiene, use antimicrobial products that do not require water (e.g., alcohol-based hand rubs) until the boil-water notice is cancelled. If hands are visibly contaminated, use bottled water and soap for handwashing; if bottled water is not immediately available, use an antiseptic.

When the advisory is cancelled:

  • Follow the local water utility’s guidance on flushing all incoming waterlines from the public water system (e.g., faucets, waterlines, and dental equipment). If no guidance is provided, flush dental unit waterlines and faucets for 1 to 5 minutes before using for patient care.
  • After the incoming public water system lines are flushed, disinfect dental unit waterlines as recommended by the dental unit manufacturer.


CDC. Guidelines for infection control in dental health-care settings – 2003. MMWR 2003; 52(No. RR-17):1–66. pdf icon[PDF-1.2M].  Accessed March 17, 2016.

US Environmental Protection Agency. National primary drinking water regulations, 1999: list of contaminants. Washington DC: US Environmental Protection Agency, 1999. icon.  Accessed March 17, 2016.

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

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;65:355–356. Accessed April 15, 2016.