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Features / November 20, 2023

Eliminating bacteria in dental waterlines

by Jane Renehan

Jane Renehan on dental waterlines

Jane Renehan answers another reader’s question relating to eliminating bacteria in dental waterlines.

The question – Dear Jane…

What is the best way to ensure that dental waterlines are clean and clear of biofilm? Is there a recommended product that is best for eliminating bacteria in waterlines?

The answer

Dental practices operate with a large variety of dental chair units, with a varying array of water systems, and use a wide range of waterline treatment products. So, what may sound like a simple question is not so simple to answer.

Regulatory oversight

The Dental Council’s revised Code of Practice Relating to Infection Prevention and Control (2015) sets out the minimum standards to which dentists should adhere. In summary, the quality of dental unit output water should fall within the potable drinking water standard set by the EU, which is 100cfu/ml of aerobic heterotrophic bacteria. The published advice reminds dentists they should also be aware of their obligations under the national legionella guidelines.

As always with compliance, written proof of adherence to the regulations is essential. Relevant documentation should be centrally filed under the heading ‘practice water management system’. These records should be easily accessible when requested by an inspector. 


Dental unit waterlines (DUWL) are a complex ecosystem. From the time the water is manufactured to when the water leaves a handpiece chuck or scaler tip, there are many stages at which the process can fail. 

Although infections associated with microbial contamination of waterlines appear to be rare, dental unit waterlines within dental chair units (DCUs) and mobile equipment such as ultrasonic scalers have, on occasion, been shown to harbour a wide variety of microorganisms including bacteria, fungi, endotoxins and protozoans in numbers sufficient to cause illness. 

Known human bacterial pathogens recovered from DUWL output water include:

  • Pseudomonas species, particularly Pseudomonas aeruginosa
  • Legionella species, particularly L pneumophila
  • Nontuberculosis mycobacterium species
  • Cryptosporidium species.


Biofilm is a layer of microorganisms composed mainly of bacteria firmly attached to a surface and protected by a slimy exopolysaccharide (EPS) material. From start to finish, biofilm can form in 72 hours within waterlines.

Dental units are predisposed to biofilm formation. This is because they have small bore, long tubes that increase the surface area, and endure periods of stagnation. In addition, there is a low flow rate with little or no disruption to the microorganisms present on the inside surface of the waterline. This biofilm provides a reservoir for ongoing contamination of dental unit output water. 

The risk to humans arises when contaminated water is ingested, as in the case of our patients. Dental teams should also be aware of the occupational hazard when contaminated water is aerosolised and inhaled or aspirated.

Managing biofilm

There is no currently available single method or device that will completely eliminate biocontamination of DUWLs or exclude the risk of cross infection. To reduce contamination risk, a combination of methods is recommended, including:

  • Using an independent water reservoir system that is separate from the mains water source
  • Flushing the DUWLs between patients, also at start and end of the day
  • Fitting anti-retraction valves on all dental handpieces
  • The use of chemical disinfectants and biocides used continuously, periodically or occasionally to shock the DUWLs
  • Automatic disinfection of DUWLs.

When selecting the best methods to maintain waterlines and monitor the water quality, always refer to the guidance from the dental unit manufacturer specific to that particular piece of equipment. 

Once a protocol is established, staff must be educated on how to execute it. Strict adherence to practice maintenance protocols is necessary to sustain the quality of dental unit water. 

But simply treating waterlines may not be sufficient to ensure water quality. The dental practice should also determine if the methods being utilised are successful. This requires a protocol that includes regular monitoring of maintenance processes. 


Flushing means letting the DUWLs run for a period of time (30 seconds to five minutes) to ensure that the same water is not retracted and used between patients, to remove residual disinfectant/biocide and to reduce the level of microorganisms in the waterlines. 

While flushing can result in a reduction in microbial density by several orders of magnitude, studies have reported that microbial levels after flushing were still unacceptably high (ie >100cfu/ml water). This is because flushing does not tackle the biofilm within the DUWLs and, therefore, is insufficient as the sole method of DUWL decontamination. 

Biocidal products

Choose only clinically proven DUWL treatment systems that have been externally reviewed. Always look for independent, external studies into the efficacy of the product. Do not rely solely on the manufacturer’s evidence. 

Most biocidal products are composed of a number of different components. Spend time researching the efficacy of a product, ensure it is suitable for your dental chair unit, get a starter kit and follow the manufacturer’s instructions exactly as written.

When you know your product, draw up your practice’s operating procedures.

Before and after periods of shutdown (eg, holidays), a more intensive disinfection protocol should be used to shock the DUWLs that will prevent any recontamination of dental units during periods of downtime. 

Some shock disinfectants can also be used as holding solutions during periods of downtime.


The only way to ensure the effectiveness of a dental unit waterline cleaning regimen is to test the water coming out of the unit. Whereas regular in-practice testing is not mandatory, it is considered to be good practice.

Sampling should be undertaken by staff trained in the appropriate technique for taking water samples and reading the results. Test results should be recorded and dated.


All dental staff involved in patient care should receive appropriate and ongoing training in managing and maintaining safe water systems. 

Details of this training should be kept on record by the practice owner. 

Induction training should be given to all new staff and staff returning to work after a period of significant absence (eg maternity leave). 

Training records should be kept for all dental staff members for a period of eight years.

Without adequate knowledge on the part of staff, the prevention and management of safe water systems is simply not possible.


The legislation requires that practices have a site-specific control plan in place for managing the occupational workplace hazards of contaminated water systems. This should include, but not be limited to, standard operating procedures (SOPs) and records for cleaning and flushing dental chair lines. 

Consult your dental supplier for guidance on the correct cleaning and disinfection process for your particular units. 

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