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DUWL’s and the risks associated with Biofilm

I get asked a lot of questions from practices around the subject of DUWL’s and the best way of maintaining them.

Water quality, within Dentistry, is an extremely important element that needs to be maintained to reduce any potential pathogen risk, in particular Legionella pneumophila. Biofilm plays a huge part in the culture and spread of these pathogens, but how do we maintain this?

As discussed, in a previous article, the longer that water is allowed to remain 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.

"Biofilms are one of the most widely distributed and successful modes of life on Earth,“*

99% of all bacteria live in biofilms which can be made up of populations of the same bacteria or of communities, which, in turn, are made up of many different species, all living together under a

protective dome.


Once the biofilm process has commenced and the polysaccharide slime formed this becomes and irreversible action and can only be removed through the use of a biocidal agent. Continual flushing of the lines will have no effect. Flushing of the lines can, however, help to prevent this from forming.


HTM discussing the need for flushing the lines for 2 mins at the start, end and after any prolonged down time, along with 20-30 seconds in between patients. This process helps to break the quorum sensing and thus reducing the biofilm formation from happening.


All Dental practices should have a copy of the L8 ACOP document, issued by the HSE, which 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:

(a) the water temperature in all or some parts of the system may be between 20–45 °C, which is suitable for growth;

(b) it is possible for water droplets to be produced and if so, they can be dispersed;

(c) water is stored and/or re-circulated;

(d) 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 which 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 in which the risk from exposure to legionella bacteria is increased.

If you believe that you may have a legionella problem, with your mains supply, then the use of a Point of Use filter would be advantageous at protecting staff and patients from the disease. These filters will stop any bacteria, down to 0.2nm, and prevent them from 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, it is recommended that water-quality sampling takes place at outlets identified as sentinel points before refitting a replacement filter. Except where taking samples as above, once point-of-use filtration has been introduced, taps or showers must not be used 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 be carried out every 3 months. This will help to provide us with the safe knowledge that we have any biofilm issues under control.

Using an additive in the water bottle will also help to slow the potential growth down, however I would also suggest that these bottles are routinely disinfected with a Chlorine solution of no less that 1000ppm.



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