The lowdown on Legionella testing

Legionella testing

When should you test for Legionella in a water supply, and what is the right test to use? With some recent major developments in testing techniques, not to mention confusion over the circumstances under which Legionella testing is required or advised, allow us to offer some advice. 

Why test?

On its website The Health & Safety Executive (HSE) stipulates that the need for Legionella testing “depends on the system that you have and the outcome of your risk assessment.”  So, when thinking about the necessity (or otherwise) to test your water, the starting point should always be the Legionella risk assessment. Therefore, it’s important to ensure that your risk assessment is current and comprehensive, as an inadequate or out-of-date document could lead to you making the wrong decision about testing.

In low risk environments, such as where a domestic hot and cold water system is enclosed i.e. doesn’t have any elements which are exposed (such as cooling towers or outside tanks), and where standard and effective Legionella control measures are in place (such as temperature checking and descaling), “microbiological testing is not usually required.”

However, for open systems, such as cooling towers and evaporative condensers, premises where there are hot tubs, swimming pools or other higher-risk components, or places where more susceptible people live (the elderly or unwell), routine testing should absolutely be part of the Legionella control system.

Be aware that there are some unscrupulous operators out there who will tell the uninitiated that they need a ‘Legionella certificate’ (or similar). This has been a particular problem in the rental property sector, where landlords have been duped into paying for unnecessary Legionella testing.

To be clear, Legionella testing is only required if the risks of bacterial growth are high (due to the design of the system or a susceptible population); if control measures have been shown to be inadequate; or that you have reason to believe that bacteria is present. Of course, if someone has become ill with symptoms of Legionnaires’ disease or the health and safety authorities stipulate that testing is required, immediate action must be taken.

Remember, testing can be a useful tool in identifying problems as well as confirming suspicions. Once you have found and dealt with an issue, it may be possible to reduce the frequency of testing if you can prove that Legionella is no longer present.

If in doubt about whether or not to test for Legionella, consult an accredited water hygiene specialist or visit the HSE website and read its guidance in HSG274 Part 2.

Who should test?

Once you’ve established that Legionella testing is required, it’s vital that it is done by a suitable person. The HSE advises that it “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.  The type of test required will depend on the nature of the water of the system.”

Again, using verified testing procedures, and ensuring that the tester is accredited by a suitable body (such as the Legionella Control Association) is extremely important. It’s also a good idea to find out which lab the testing company will be using to analyse the results; they need to be UCAS-certified and should take 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.

We are proud to work with Cheshire Scientific, one of the leading microbiological laboratories in the UK to provide our sampling and testing results.

How to test?

There are now a number of different procedures available to test for Legionella, from the latest in-field kits which claim to deliver an accurate result on-site within minutes, to the more traditional lab culture technique which gives results within about 10 days.

The HSE advises that “the sampling method should be carried out in accordance with BS7592” and in its guidance it provides detailed information on the types of test available and what to do in the event of a positive result.

When choosing the most appropriate testing technique for your situation, take into account the complexity of the water system as this will also help you to determine the right number of samples to take.  Frequency of testing is another variable to consider: in some situations a quarterly test will be enough, but in others sampling should be done monthly or even weekly. Your testing provider should be able to advise on the most appropriate timescale.

The HSE says that samples should be “representative of the water flowing around the system and not just of the area downstream of the fitting” and samples should be taken from separate hot and cold outlets instead of from mixer taps or outlets downstream of TMVs or showers. It may be obvious, but always make sure that samples are clearly labelled with their source location and also note whether they are collected pre- or post-flushing.

What next?

In our next blog we will look at the interpretation of testing results and what you should do in response to the findings. If you have any questions in the meantime, or need to carry out Legionella testing, contact us.