The problem with dental unit waterlines 

The problem of microbial contamination in dental unit waterlines is the result of how water is used during routine dentistry and the design of the dental equipment itself. Factors including small-diameter waterlines, low flow rates, long periods of stagnation, improper waterline termination, and even occasional backward contamination from the patient to the delivery system all contribute to microbial contamination.

The unfortunate reality is that even quality input water can quickly become contaminated in dental unit waterlines. Even a single microorganism that survives filtration and chemical treatment can replicate exponentially. As such, microbiological contamination of dental unit waterlines is a challenging issue that must be addressed rigorously. 

Dental bottles and direct connections 

Years ago, in an attempt to combat this contamination issue, dental delivery system manufacturers introduced independent bottle systems. These bottle systems provide delivery units with an independent source of water not connected to the city water supply and typically hold between 750 milliliters to two liters of water. 

The basic line of thinking with these systems was essentially that more control over the quality of the input water to the system via independent bottles would enable higher quality output water. While this idea sounded very reasonable in theory, it wasn’t sufficient in practice without proper cleaning and maintenance of dental bottle systems. 

Even returning a dental bottle filled with otherwise sterile water to its manifold can introduce contamination. Airborne bacteria and microbes present on the surface of the riser tube reinserted into the bottle can instantaneously introduce contamination back into the system. Furthermore, regardless of how the water is delivered, the bacteria will eventually recolonize the water within the system, regardless of delivery methods. 

To avoid complications with bottle systems, some practitioners choose to plumb their delivery units directly to the city water supply, but this method can also prove to be a challenge to finances and quality. For instance, many local plumbing authorities disallow direct connections to the public water supply without expensive backflow prevention devices installed for each operatory. Furthermore, some dental practices may have trouble paying for the mandatory shock treatment that will need to be administered to direct waterlines. Regarding quality concerns, city water often contains sediment, scale and fine particulate matter that can harm dental equipment. 

Dental waterline maintenance protocols 

Whether dental operatories are plumbed directly to municipal water supply lines, utilize independent bottle systems, or have a water filtration system installed, the following protocols and guidelines should be observed at all times for dental waterline maintenance: 

• Discharge air and waterlines for a minimum of 20-30 seconds after each patient, as recommended by the Centers for Disease Control and Prevention (CDC). This procedure is intended to flush out patient material that might’ve entered the handpiece turbine, air or waterlines. 
• Don’t 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. 
• Monitor water quality throughout the operatory environment at least quarterly by submitting water samples to a laboratory for heterotrophic plate count (HPC) testing, or by using an in-office testing product, to ensure compliance with water-quality standards of <500 colony-forming units (CFU) of bacteria per milliliter, as recommended by the CDC. 

Further, if using any type of water filtration system — whether plumbed directly to the dental delivery unit or for filling dental bottles — it’s important to follow the manufacturer’s Instructions for Use (IFU).