Decon Pete – water quality and the potential risks of legionella

decon peteThis month Decon Pete discusses legionella formation and things to consider when reopening dental surgeries.

Water quality, within dentistry, is an extremely important element that needs maintaining to reduce any potential pathogen risk. In particular legionella pneumophila.

Dental practices have, for some time now, not been operating at full capacity. With many utilising additional surgeries for the donning and doffing of PPE.

With these surgeries not in use, as initially intended, it could result in issues with the water lines that staff members might not notice.

The surgery taps, unless run routinely every day, would result in dead legs forming in the water system. These dead legs are a perfect breeding ground for pathogens such as legionella.

Legionella formation

As discussed, in a previous article, the longer that water remains static the greater the chances of biofilm formation.

Biofilms form when individual bacteria, in a water line/pipe, adhere to the tube surface. When many bacteria adhere, a mechanism called quorum sensing changes the way that the adhered bacteria behave. The adhered bacteria then secrete a protective polysaccharide slime, forming a continuous film.

All dental practices should have a copy of the L8 ACOP document, issued by the HSE. It describes the following:

Legionnaires’ disease is normally contracted by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella if:

  1. The water temperature in all or some parts of the system is between 20-45°C, which is suitable for growth
  2. It is possible for water droplets to produce and if so, they can disperse
  3. Water is stored and/or re-circulated
  4. There are deposits that can support bacterial growth, such as rust, sludge, scale, organic matter and biofilms

It is important to control the risks by introducing measures that do not allow proliferation of the organisms in the water systems and reduce, so far as is reasonably practicable, exposure to water droplets and aerosol.

This will reduce the possibility of creating conditions for legionella bacteria to grow.

Reopening the dental surgery

Before reopening an unused surgery we need to ensure that we have run through a few things.

Ensure that a biocidal agent is run through the treatment centre as part of the re-commissioning procedure. Run the cold water supply for two minutes and ensure that the temperature doesn’t exceed 20°C.

Run the hot water supply for one minute and ensure that the temperature doesn’t drop below 50°C.

If you believe that you may have a legionella problem with your mains supply, then the use of a Point of Use filter is advantageous at protecting staff and patients from the disease. These filters will stop any bacteria, down to 0.2nm. And they prevent further transmission.

UK guidance documents has the following to say about POU filters:

‘19.63: Point-of-use filters must be changed in accordance with manufacturers’ recommendations, typically at least once a month. When changing filters, we recommend water-quality sampling takes place at outlets identified as sentinel points before refitting a replacement filter. Except where taking samples as above, once introducing point-of-use filtration, practices must not use taps or showers without a filter in place.’

To ensure that we have good quality water and no significant biofilm issue, I would also recommend the use of a microbiological dip slide carried out every three months.

This will help to provide us with the safe knowledge that we have any biofilm issues under control.


If you would like to discuss anything further, including Point of Use filters, then please drop me an email at [email protected] or visit www.deconpete.co.uk or give me a call 07581 309835.

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Catch the previous Decon Pete columns:

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