We've discussed some of the factors that contribute to the problem of microbiological contamination in dental unit waterlines. In this brief article, we’ll outline the dental waterline standards in place for microbiological water quality. In order to verify compliance with these guidelines, dental practices should 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.
It will be helpful to start with a couple of definitions:
Heterotroph: an organism that cannot manufacture its own food, and instead obtains its food and energy by taking in organic substances, usually plant or animal matter. All animals, protozoans, fungi, and most bacteria are heterotrophs.
American Heritage Science Dictionary (2002)
For purposes of this article, we’ll consider only heterotrophic microorganisms in water. Quantities of these microorganisms in drinking water (and other media) are typically measured in terms of plate count—or in this case, Heterotrophic Plate Count (HPC).
Plate count: a determination of the degree of bacterial contamination of a sample made by enumeration after a period of incubation of the colonies appearing in a plate that has been inoculated with a suitable dilution of the sample.
Merriam-Webster Dictionary (2016)
HPC testing has a long history of use in water microbiology, and has been employed since the 19th century as an indicator of proper functioning of various means of processing water. Microorganisms recovered and measured through HPC tests are typically normal, environmental—and usually non-hazardous—organisms. Therefore, HPC testing can only provide an indirect indication of water safety.
Because HPC testing provides a good, general indication of the degree to which a water system has been regularly maintained, both the Centers for Disease Control and Prevention (CDC) and the American Dental Association (ADA) recommend that water used in non-surgical dental procedures meet the EPA’s former regulatory standards* for drinking water: less than or equal to 500 colony-forming units (CFUs) of heterotrophic bacteria per milliliter of water.
Water Quality Goals (HPC):
- <500 CFU/mL (CDC)
- <500 CFU/mL (ADA)
- <100 CFU/mL (European Union)
In a previous blog entry, we discussed several factors that contribute to the problem of microbial contamination of dental unit waterlines. Because of these factors, even the ideal-quality input water can quickly become contaminated inside dental delivery systems.
Bottom line: due to the nature and complex design of dental delivery units, the periodic use of waterline cleaners and antimicrobials is extremely important for proper dental waterline care, and to meet the water quality goals set forth by the CDC, ADA and EU.
Want to become a dental-water expert?
Water quality affects nearly every function of modern dental offices. Our (free!) eBook, The Book on Dental Water, is designed to help you understand how using the right water can help to improve patient care, staff productivity and practice profitability, while also protecting the investments you’ve made in the equipment and appliances in your office.
* EPA standards for HPC in public water used to be 500 CFU/mL, but is now “N/A” for HPCs. According to 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.”