Below you will find a guide, provided by Sean Green, Head of Operation (Water Hygiene) on the process of testing and monitoring water systems.

Who can be appointed to test or monitor Legionella?

Testing of water quality may be carried out by a service provider, such as a water treatment company or consultant or by the operator, provided they are trained to do so and are properly supervised.

How do I test or monitor Legionella from my water system?

Where monitoring for Legionella is considered appropriate, the sampling method should be carried out in accordance with BS7592 and the biocide, if used, neutralised where possible. Water samples should be tested by a UKAS-accredited laboratory that takes part in a water microbiology proficiency testing scheme such as that run by Public Health England. The laboratory should also apply a minimum theoretical mathematical detection limit of <= 100 Legionella bacteria per litre of sample for culture-based methods.

How often should I test water for Legionella?

It depends on the system that you have and the outcome of your risk assessment. For open systems, such as cooling towers, evaporative condensers and spa pools etc, routine testing should be carried out at least quarterly. However, there may be circumstances where more frequent sampling may be required.

For hot and cold water systems, which are generally enclosed, i.e. not open to the elements and significant contamination in the same way as cooling towers, microbiological monitoring is not usually required. However, there may be circumstances where testing for Legionella is necessary, for example where there is doubt about the efficacy of the control regime or where recommended temperatures or disinfection concentrations are not being consistently achieved.

How do I interpret Legionella test results?

To interpret your test results, you should consider what they mean in the context of your water system as your subsequent specific actions will depend on your risk assessment. Franks Portlock can interpret the results and provide you with the best course of action to not only rectify the immediate issue, but what to do to prevent recurrence.

You can find out more about our water hygiene services here or speak to a member of our team to see how we can support you with water testing here.


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