Dental mythbuster 5: Legionella and dental waterline management

Page last updated: 16 June 2023
Organisations we regulate

Our priority is to carry out an assessment of the quality of primary care dental services. From this we make a judgement about whether they provide people with care that is safe, effective, caring, responsive and well-led, based on whether the regulations are being met.

Our inspectors will consider the topic of legionella and dental waterline management when they review ‘safe’, which relates to regulation 15 (premises and equipment).

According to HTM 01-05: Decontamination in primary care dental practices ‘Registered Managers of dental practices have an overriding general duty of care under the Health and Safety at Work Act 1974’. Part of this duty of care is ensuring that the water supply, storage and distribution services should comply with the best practice guidance given in:

Legionella bacteria and other organisms live in water supplies; some are completely harmless, whilst others such as Mycobacteria spp and Pseudomonads can cause disease. Water companies are required to keep them within the very strict limit of 100 Colony Forming Units (CFUs). These organisms are part of ' biofilms' which form rapidly in dental waterlines because:

  • there is a source of nutrients for the bacteria
  • ‘plasticisers’ present in the plastic tubing of the waterlines system
  • warmish water (ambient temperatures in surgeries can be quite high), and
  • water in the system can remain stagnant overnight and at weekends.

Research reveals that bacterial counts in waterlines can be colossal; one study showed colony sizes of 19,500 CFUs compared to 100 CPUs in the drinking water supplies. Remember, water in dental waterlines is going into patients mouths, comes into contact with open wounds as a result of oral surgery and is swallowed by patients. There is also potential for occupational risk to the dental team from exposure to contaminated dental unit waterlines aerosols. Likewise vulnerable patients such as those suffering from chronic respiratory diseases, alcoholics, diabetics and immuno-compromised patients may potentially be at increased risk of respiratory infection or colonisation from inhaling contaminated aerosols during dental treatment.

Professional guidelines:

Mandatory requirements

  1. All systems require a risk assessment, however not all systems will require elaborate control measures.
  2. All premises are required to have a written waterline management scheme and legionella risk assessment. These schemes should be written by experienced and competent people. A competent person is someone with the necessary skills, knowledge and experience to carry out this function.
  3. The registered manager must ensure that all the recommendations of the written scheme and risk assessment are implemented
  4. Water and air lines must be fitted with anti-retraction valves in accordance with EU regulations
  5. It is mandatory to control Legionella within the dental waterline system, but there is no one single system of treatment which is 100% effective.

Recommended practice

  1. How should dental waterlines be maintained? A variety of products are available to disinfect waterlines and they should be used periodically according to manufacturer’s instructions. Not all products completely remove biofilm so regular dosing according to manufacturer’s instructions is required to control the bacterial count. These products can be used by practice staff making up the required amount for the bottle at the side of the unit or with a dosing device. However, with all these products, the default position is the dental chair unit manufacturer’s instructions; there may be manufacturers who don’t recommend their use. In tandem with using these products, waterlines should be regularly flushed. A typical regime is as follows:
  • To reduce microbial accumulation, run water through the water lines for 2 – 3 minutes at the start of each session and 20 – 30 seconds between every patient. Checklists are useful to ensure compliance and provide auditable evidence.
  • At the end of the day, the bottle should be disconnected, emptied, rinsed and stored inverted clean and dry overnight. However, this is dependent on the system used to disinfect the waterlines.
  • Isolate the water supply from the mains water by using an independent bottled water system on the unit.
  • Fill the bottle with freshly distilled / reverse osmosis water at the start of each day (if bottled water is used this must be from a previously unopened bottle).
  • Do not fill bottles with tap water as this will introduce opportunistic respiratory bacteria into the waterline and rapidly lead to biofilm formation.
  1. Do dental water lines require routine microbiological monitoring? Apart from situations where there are taste or odour problems, microbiological monitoring for total viable counts is not considered to be necessary.
  2. How often should the water be tested for Legionella? This depends on the system in place and the outcome of the risk assessment.
  3. How often should the temperature of the system be checked? This depends on the outcome of the risk assessment and the components of the system.