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Practical Approaches to Dental Unit Water Management

The proper management of dental unit water systems will help ensure the provision of safe care.

The proper management of dental unit water systems will help ensure the provision of safe care
This course was published in the June 2019 issue and expires June 2022. The author has no commercial conflicts of interest to disclose. This 2 credit hour self-study activity is electronically mediated.

SECOND IN A TWO-PART SERIES: This is the concluding installment of a two-part series. Appearing in April 2019, Part 1 (available at decisionsindentistry.com) offers an overview of biofilm contamination in dental waterline systems, as well as management recommendations designed to ensure safe treatment water.

Due in part to headline-making infection control breaches involving dental treatment water, patients and the profession are placing increased scrutiny on dental waterline asepsis. The provision of safe care demands that offices follow recommended infection prevention protocols, and managing dental unit waterlines (DUWLs) is a foundational element of any successful program.

The first article in this series (available at decisionsindentistry.com) explores the nature of dental water systems and why these designs foster biofilm colonization. It also provides an overview of DUWL management guidelines and resources that practices can use to comply with dental water safety standards. This concluding installment will focus on specific approaches and recommendations for DUWL maintenance and testing.

Due to intermittent water flow through long, complex and narrow-bore tubing systems, DUWLs encourage, and even amplify, the formation of waterline biofilms that may contain pathogens, including Pseudomonas aeruginosa, nontuberculous mycobacteria, and Legionella species that can be released into treatment water.

Consequently, the U.S. Centers for Disease Control and Prevention (CDC), professional organizations, such as the Organization for Safety, Asepsis and Prevention (OSAP), and dental companies offer recommendations and resources to help offices comply with the CDC’s suggested dental water standard. For routine dental treatment, the CDC limits DUWLs to ≤ 500 colony forming units of heterotrophic (non-coliform) water bacteria per milliliter (CFU/ml).1,2 This matches the federal Environmental Protection Agency (EPA) standard for drinking water.

A dental waterline management protocol should be included in every facility’s written safety program and should contain relevant laws and formal recommendations, along with specific information regarding the equipment used, procedures performed, and the germicidal products and processes employed in DUWL maintenance (Table 1). Instructions for use for all equipment and products should be available and followed. The protocol must stipulate regular DUWL testing to ensure compliance with water standards. If surgical care is provided, written and physical methods for complying with the sterile irrigation standards must be available. Patient records should document sterile fluids used for surgery.

The CDC provides the most widely recognized and frequently referenced recommendations for dental safety. In its seminal Guidelines for Infection Control in Dental Health-Care Settings — 2003,1 and 2016 follow-up, Summary of Infection Prevention Practices in Dental Settings: Basic Expectations for Safe Care,2 the CDC provides a wealth of resources for DUWL management practices. Written schedules and checklists are efficient ways to manage processes — such as ongoing DUWL asepsis treatment and periodic shocking — and checklists included in the 2016 document may prove helpful in complying with dental water treatment standards.


Waterline cleaners and germicides fall under two main categories. Shock treatment products are used to remove established, attached DUWL biofilms. (Note: These products are caustic and clinicians should avoid contact with skin or mucosal tissues.) Low-level germicides are used to reduce planktonic biofilm and retard its attachment and growth. These agents should be continuously present within the dental water system, and are safe for patient treatment.

Shock product options are limited and chiefly consist of two chemical choices: bleach, and a hydrogen peroxide-based formula that is approved by the EPA for use overnight in DUWLs. Diluted to a concentration of 13:1 and used for a maximum of 10 minutes, bleach has been studied extensively and is generally considered effective for removing DUWL biofilms, but practical issues must be considered, such as corrosion if left in the lines for more than 10 minutes and possible damage to room surfaces. Bleach is not EPA approved for this purpose, however, and its use is considered off-label.

As a professional organization specializing in dental asepsis, OSAP does not recommend off-label use of germicides or cleaning agents that do not have regulatory approval and are not federally registered for the control of biofilm in dental equipment.3 For example, non-EPA-registered waterline cleaners without germicidal claims are available and used off-label, but may yield varied and unpredictable results. Water testing can be used to monitor product efficacy.

Shock treatment is recommended prior to beginning a regimen of daily DUWL management with a low-level maintenance product or other system, as well as periodically to remove accumulated biofilm. Shocking recommendations are important because biofilms should be removed prior to implementing daily or automatic, system-based waterline management programs. In addition, DUWL biofilms have the potential to build up when an office uses a daily, low-level germicide that is safe for patient care. While some manufacturers suggest a time interval for periodic shocking, many do not. If no shock interval is recommended, the most reliable method for determining the need for shock treatments is to test output water.


Practices can also choose independent water reservoirs that isolate dental units from municipal water systems and provide immediate access to dental waterlines for intermittent- or continuously present cleaners or germicides. Manufacturers now offer equipment with separate water bottles due to the well-established criteria for water maintenance. Older units without separate reservoirs can be retrofitted with bottles to provide access for treating irrigation water. These should be filled with high-quality treatment fluid and cleaned and maintained aseptically, according to the equipment and water germicide manufacturers’ directions.2–5

Automated germicide metering or slow-release devices, which may include filtration technology that can be used with independent reservoirs or municipal water connections, are another option for DUWL management. Cartridges that may filter the water — as well as release antimicrobials into DUWLs — may be located in the reservoir as an uptake “straw” or installed at other locations, such as the junction box of each dental chair or at a central location to treat multiple chairs simultaneously. The cartridges allow treatment of municipal water or water from sources that may be treated in some manner, such as by ultraviolet, filtration or ionization processes. The remote location of the cartridges and the chemical or other design features may be affected by shocking treatments, or even make shocking difficult or impossible. Adding to this challenge are differing instructions from various manufacturers regarding the need to shock or frequency of recommended shocking. Water testing shows that all DUWL management systems may fail to control contamination4 and DUWLs are likely to require shock procedures, even though some manufacturers claim such protocols are unnecessary. The ability to shock and recover any system after a water test failure is an important component of safe care.4

Sterile water delivery systems, which employ sterile, disposable or heat-sterilized reusable components that are independent of the dental unit water supply, are indicated for surgical procedures. Peristaltic pumps, bulb syringes, other syringe types, and removable, sterilizable devices bypass the DUWL and are indicated when use of a sterile standard is appropriate.

Distillers, reverse osmosis and microfiltration devices can remove microorganisms from procedural water entering the dental unit, but do not effectively limit the growth of biofilm after water enters the DUWL or reservoirs. These devices and processes may also produce water with high bacterial counts due to hidden and undetected biofilms. Strict protocol for preventing biofilm contamination in the devices or in stored water supplies must be followed. Studies show that samples of treated dental water may contain higher CFU/ml than tap water due to the residual levels of chlorine, more rapid water flow, and larger plumbing size of tap-water lines.4 Because water filters trap particulates, chemicals and organisms, filters are potential sources of water contamination and must be regularly maintained. In addition, dental units may contain hidden or difficult-to-access filters that cultivate bacteria and fungi.6,7


Dental water systems should be regularly monitored (i.e., tested) to validate management protocols or identify potential contamination. The CDC and OSAP recommend using DUWL tests as action limits that help prompt maintenance procedures, such as shocking.3 Monitoring methods include in-office sampling and laboratory testing.

All methods of waterline testing are inherently limited, however, as they capture only representative heterotrophic organisms that are used to estimate levels of non-coliform bacterial contamination. Routine testing reveals the range of CFU/ml of non-coliform organisms in water (potability), while specific tests to identify individual species are expensive and typically only done to investigate cases of suspected exposure. While in-office monitoring is simple, convenient and costs less than laboratory testing, it has been found to provide more limited and less reliable results.8,9 Available from dental supply companies, these basic tests are designed to reveal contamination levels ≤ 300 CFU/ml. In clinical practice, in-office tests may be useful as quick checks for well-managed waterlines between more reliable lab tests to provide early warning of potential contamination.3,4,8,9

When using laboratories for DUWL testing, practices must follow directions for aseptic collection and shipping of samples. The laboratory should provide results similar to sterilizer monitoring reports, and the practice should log these records. (In-office test results should also be recorded.) Dental waterline testing companies and universities may provide consulting services that assist offices in correcting errors, and it has been shown that repeated testing with professional guidance leads to improved results.


Best practices for dental water system monitoring, as recommended by the CDC1,2 and OSAP,3 include the following:

  • Clinicians are encouraged to follow manufacturers’ recommendations for frequency of inspection and monitoring of DUWL-related devices
  • If no recommendations are available from the equipment manufacturer, follow recommendations from the germicide or DUWL treatment product manufacturer
  • Per OSAP, periodic monitoring and inspection should be performed at least monthly on each dental unit or device following installation, maintenance or repair of treatment devices; this also pertains to initiation of new protocols — including new reservoirs, or after periods of disuse and/or lack of maintenance
  • If monitoring indicates that water quality is acceptable for two consecutive monthly cycles, the frequency of testing may be reduced — but should not be less than every three months
  • When a DUWL exceeds the action limit for an initial or periodic test, the system should be treated according to manufacturer instructions and retested immediately after treatment3


The safety concerns associated with waterline maintenance underscore the need for dental teams to adopt — and consistently practice — effective management strategies.1–3 The following discussion highlights clinical approaches designed to ensure compliance with dental water-quality standards.

Practices are encouraged to use an EPA- or U.S. Food and Drug Administration-approved system to control waterline contamination, which may include equipment purchases or use of germicide products — or both.

Clinical teams should receive education and training regarding the importance of DUWL management protocols. As noted, a waterline management plan should be part of every office’s written infection control program and should include standard operating procedures, as well as a schedule for testing and treatment. If the manufacturer of the DUWL-related device or treatment does not provide relevant instructions, consult the reference documents identified here and regularly test water to ensure compliance. In order to maintain DUWL water-quality standards, all components of the equipment, including reservoirs and detachable devices (such as ultrasonic scalers), should be treated.

Dental offices may consider installing separate water bottles (even when using an inline antimicrobial treatment cartridge) for the purpose of gaining access to the system to introduce chemicals, such as shock treatments.

It is important to realize that filtered, treated or distilled water is not sterile and may have undetected microbial contamination. Excellent source water does not preclude the need to treat dental waterlines.

In clinical practice, teams should avoid introducing DUWL contamination resulting from handpiece retraction or other equipment-related causes. It is also advisable to identify DUWL design features that may potentially undermine water quality, such as inline filters that must be routinely changed, or dead legs of tubing that can be eliminated. Offices may also wish to consider replacing waterlines in older dental units.

Waterlines should be flushed for 20 to 30 seconds between patients — and at the beginning and end of each day — to eliminate planktonic contamination and any material retracted during treatment.

Practitioners should not confuse flushing with shocking. Flushing waterlines is recommended to move fluids through lines, but provides only temporary clearing and does not reliably eliminate attached biofilm. Chemical shocking is used to remove established biofilm, and all hoses, devices and ports should be treated. While some waterline product manufacturers claim that shocking is not required, data show that biofilms may regrow over time.

Teams should evaluate the effectiveness and concentration levels of chemicals used to treat waterlines. Many factors (such as pH) affect the concentration of daily or extended-use products, and it is advisable to replace products before they are entirely depleted. Testing can shed light on product efficacy.

Using an aseptic technique to draw samples, waterlines should be tested monthly after installation, repairs, or changes in equipment or protocols until tests confirm the output meets potable water standards of ≤ 500 CFU/ml heterotrophic (non-coliform) bacteria. After safe levels are met — and assuming results prove consistent — testing may be conducted every three months.1,3,4,10


Ensuring safe treatment water requires investing in a DUWL management system, using it correctly and consistently, and assessing the results through testing. Commercial options for maintaining waterlines are abundant, so there is an appropriate solution for every clinical setting. In light of the increasing scrutiny on DUWL asepsis, it behooves oral health professionals to follow recommended protocols designed to protect patients and practitioners.


  1. Kohn WG, Collins AS, Cleveland J, Harte JA, Eklund KJ, Malvitz DM. Guidelines for Infection Control in Dental Health-Care Settings — 2003. MMWR Recomm Rep. 2003;52(RR17):1–61.
  2. U.S. Centers for Disease Control and Prevention. Summary of Infection Prevention Practices in Dental Settings: Basic Expectations for Safe Care. Available at: https:/​/​www.cdc.gov/​oralhealth/​infectioncontrol/​guidelines/​index.htm. Accessed February 26, 2019.
  3. Mills SE, Porteous N, Zawada J. Dental Unit Water Quaility: Organization for Safety, Asepsis and Prevention White Paper and Recommendations — 2018. Available at: https:/​/​osapjdics.scholasticahq.com/​article/​5075-dental-unit-water-quality-organization-for-safety-asepsis-and-prevention-white-paper-and-recommendations-2018. Accessed February 26, 2019.
  4. Dewhirst N, Molinari JA. Treating and monitoring dental water. Compend Contin Educ Dent. 2018;eBook:11–21.
  5. Dental Board of California. Appendix 3 Dental Board of California Infection Control Regulations. California Code of Regulations Title 16 Section 1005. Available at: https:/​/​www.dbc.ca.gov/​lawsregs/​index.shtml. Accessed February 26, 2019.
  6. Kim AS, Chen H, Yuan R. EPS biofouling in membrane filtration: an analytic modeling study. J Colloid Interface Sci. 2006;303:243–249.
  7. Wright SJ, Semrau JD, Keeney DR. Microbial fouling of a reverse osmosis municipal water treatment system. Water Environ Res. 2008;80:703–707.
  8. Karpay RI, Plamondon TJ, Mills SE. Comparison of methods to enumerate bacteria in dental unit water. Curr Microbiol. 1999;38:132–134.
  9. Momeni SS, Tomline N, Ruby JD, Dasanayake AP. Evaluation of in-office dental unit waterline testing. Gen Dent. 2012;60:e142–e147.
  10. American Dental Association. Nontuberculous Mycobacterial Infection Linked to Pulpotomy Procedures and Possible Dental Waterline Contamination Reported in California and Georgia. (September 21, 2016.)


From Decisions in Dentistry. June 2019;5(6):42–45.

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