What to Do about Dental Unit Waterline Contamination

Jim Chandler


Your dental unit waterlines are very likely contaminated. As discussed previously, dental unit waterline problems result mainly from how water is used in the operatory and from the design of dental delivery units: 

  • Low flow rates and long periods of stagnation
  • Small-diameter waterlines and high surface-to-volume ratio
  • Increasing water temperature
  • Waterline termination, or “dead legs”
  • Contaminated source water and “suck back” from patients.

Years ago, delivery system manufacturers introduced independent bottle systems primarily to mitigate issues with municipal source water. While filling bottles with purified water helps by removing certain contaminants and dissolved solids commonly present in city water, using bottle systems does not solve the other issues that contribute to waterline contamination.

In fact, if not rigorously maintained, independent bottle systems can make waterline problems worse. Having to remove bottles to refill them exposes delivery systems to additional environmental contaminants. It’s basically like causing small water-main breaks every day!

Even sterile water can become contaminated very quickly once it enters the dental delivery system. That’s why it’s extremely important to follow a 3-pronged approach to proper dental waterline care:

  • Following basic waterline protocols daily
  • Testing waterline contamination periodically
  • Using waterline cleaners and antimicrobial agents regularly.

Let’s discuss each necessary component of this comprehensive approach one at a time.

Daily Waterline Protocols

Regardless of whether dental operatories are plumbed directly to municipal water supply lines or utilize independent bottle systems, and regardless of the presence or absence of any water filtration system that might be installed, the following protocols and guidelines should be observed at all times:

  • Purge all water-bearing lines at the beginning of each work day by flushing the waterlines thoroughly with water for a minimum of 2 minutes. This should include all handpiece, syringe, and quick-disconnect lines with handpieces and tips removed.
  • Purge all water-bearing lines for a minimum of 20 seconds after each patient, as recommended by the CDC and Canadian guidelines.
  • Do not use waterline heaters, as they serve to increase the growth rate of any microorganisms that might be present in the lines tremendously.
  • Never use water from a standard dental delivery system during surgical procedures. Instead, use sterile water or saline delivered by sterile means, such as autoclavable bulb syringes or autoclavable or disposable sterile tubing.

Anecdotally, I’ve seen levels of microbiological contamination reduced by 90% or more simply by following waterline purging protocols consistently. That said, testing water samples periodically and using waterline cleaners and antimicrobial agents regularly are both critical components of proper dental waterline care.

Dental Waterline Testing

The microbiological quality of water is often quantified by heterotrophic plate count (HPC). This time-tested method of gauging water quality dates to the 19th century, and it provides a good general indication of how well a water system is being maintained by counting the number of colony-forming units (CFU) of bacteria that a water sample contains.

Both the CDC and the ADA have set guidelines for the dental industry based on HPC counts. The CDC and ADA both recommend that water used in nonsurgical dental procedures contains fewer than 500 CFU/mL.

This threshold is based on a former standard originally set forth in the Safe Drinking Water Act, which once specified 500 CFU/mL HPC for public water. However, the Environmental Protection Agency’s standard for HPC is now “N/A” because, according to the EPA’s National Primary Drinking Water Regulations:

“HPC measures a range of bacteria that are naturally present in the environment and has no health effects; it is an analytic method used to measure the variety of bacteria that are common in water. The lower the concentration of bacteria in drinking water, the better maintained the water system is.”

To verify compliance with this guideline, I always recommend that dental practices spot-check their water quality throughout the operatory environment at least quarterly by submitting water samples to a laboratory for HPC testing or by using some type of in-office testing product.

Waterline Cleaners & Antimicrobial Agents

Due to the nature and complex design of dental delivery units, the periodic use of waterline cleaners and antimicrobial agents is extremely important for proper dental waterline care. As mentioned earlier, even sterile water introduced to dental delivery systems can become contaminated very quickly and exceed CDC and ADA-recommended guidelines for maximum microbiological contaminant levels of 500 CFU/mL.

At a minimum, practices should use a strong, antimicrobial “shock” treatment in waterlines on at least a quarterly basis, or as needed, as indicated by HPC test. This type of powerful antimicrobial treatment, conducted only when patients are not being treated, should be performed if bacteria count ever exceeds the 500 CFU/mL threshold.

In addition to periodic “shock” treatments, some practices find it beneficial to use some type of residual chemical waterline treatment on a daily basis, during the normal course of patient care. Most of these products utilize compounds of chlorine, silver, or iodine—each of which has its own pros and cons that should be taken into account considering the total office environment and in consultation with knowledgeable dental dealers and equipment representatives.


Dental unit waterline contamination is a nearly universal (and often overlooked) problem that, if left unchecked, can have serious ramifications for dental practices and their patients.

Dental practitioners understand that a comprehensive approach to good oral health involves regular brushing and flossing, periodic in-office cleanings and exams, and a healthy diet. In much the same way, a 3-pronged approach to waterline “health” consisting of following basic protocols daily, testing contamination periodically, and using antimicrobial agents regularly is best for preventing, monitoring, and controlling microbial growth comprehensively.

Mr. Chandler has nearly 40 years of experience in water treatment technologies. He is the founder and president of Vista Research Group, which provides a complete line of water treatment, purification, and steam processing solutions used by thousands of dental practices throughout the United States and Canada. He holds multiple patents; a bachelor’s degree with concentrations in conservation, biology, and chemistry; and a master’s of higher education administration degree from Kent State University. And, he is the author of The Book on Dental Water, which is available now in multiple formats at thebookondentalwater.com. He can be reached at jim@vistaresearchgroup.com.

Disclosure: Mr. Chandler is the author of The Book on Dental Water and the president of Vista Research Group, which manufactures several products designed to meet the water treatment, purification, and processing needs of dental practices.

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