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Testing for Legionella – When & How Often Should You Do It?

If you are an employer or someone in control of premises, you must understand the health risks associated with Legionella. And testing for legionella plays a key role in achieving this. Therefore, the importance of regular testing the water systems cannot be overlooked.

We are often asked this question how often should water systems be tested for legionella? With so much information available on HPSC National Guidelines for the Control of Legionellosis in Ireland, 2009 document, and also on UK HSE’s ACOP L8 & HSG274, it is easy to become overwhelmed with the sheer amount of checks, testing and requirements set out to ensure water hygiene compliance.

In this blog, we try to explain situations when legionella testing required and how often should it be done.

Why Should Legionella testing be carried out regularly?

Legionnaires Disease is a potentially deadly bacterial illness. Because of this, there are potentially high financial costs for businesses or property owners who fail to comply with their legal obligations for risk assessment and risk management.

It’s important to note that an outbreak of Legionella doesn’t have to occur in order for a business or property owner to be found legally liable. If they’re found to have been neglectful in terms of risk assessment, risk management, or record-keeping, for instance, they risk a substantial fine, whether or not a Legionella outbreak occurs—and whether or not Legionella is present in the water system at all.

For both health and legal reasons, it’s vital that business owners and rental property landlords carry out regular routine testing for Legionella bacteria.

Water testing is the only way to determine whether Legionella is present in a water system. Because of this, and because of the risks of Legionella exposure, it’s critical that water systems are regularly tested for the bacteria.

When is legionella testing required?

The frequency that Legionella testing is required will depend on several factors including the size and type of water systems involved.

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.

Which takes us back to the question of how often should water be tested for Legionella?

HPSC guidelines recommend that Legionella testing should always be carried out in situations where

  • A water system is being treated with biocides and water is stored or distributed at lower temperatures
  • The control levels of the treatment regime, eg temperature or disinfectant concentrations, are not being consistently achieved
  • There is a population with increased susceptibility (healthcare premises including care homes)
  • A water system is suspected or identified in a case or outbreak of legionellosis

Water systems such as cooling towers, evaporative condensers and spa pools etc, should be tested at least quarterly.

More frequent sampling should be carried out when commissioning a system and establishing a treatment programme or when conducting a review of the system/risk assessment to help establish when the system is back under control.

Some sectors are, particularly at an increased risk. Water storage systems found within healthcare properties, leisure centres and hotels are at higher risk compared to office blocks and factories for example.

The actual physical risks from a given water system increase with the complexity and age of the water system.  The bigger the water system the more likely it is to have dead legs and temperature disparities. These increase the risk of biofilm build-up and Legionella growth. As a result, the bigger and older a facility the more often testing would be recommended.

Determining Sampling Points & Frequency

Water testing frequency can vary from one per month, to once per day and even once per hour and should ideally be based on risk.

Each water system is different and you will have to look at its design, inherent risks and how it is performing to work out where to take water samples, and how many samples to take.

The key to any legionella sampling programme is to make sure that you are getting a representative sample of all of the water in the system. Water samples should be taken from both hot and cold outlets rather than a mix of warm and cold water flowing through a mixer tap.

Consideration should be given to areas of higher risk, especially where water temperatures drop out of specification, where stagnant water may be sitting in pipes or tanks, as well as that which regularly flows through the system.

It’s good practice to label samples clearly with details of the outlet, the date and where they were taken from. This procedure allows for easy identification once the legionella testing results are available.

Another recommendation is to “flush” the water system when taking samples.

A pre-flush sample is water collected immediately after the tap or fitting is opened. The tap or fitting should not have previously been disinfected, or water run to waste. The pre-flush sample represents water held within the tap or fitting and ideally, should be taken when the tap has not been used for several hours

A post-flush sample is water collected after the tap or tap fitting has been disinfected and water in the fitting has run to waste. The post-flush sample represents the quality of circulating water supplied to the tap or fitting.

A pre-and post-flush sample should be taken at all outlets sampled.

Expert Legionella Testing & Sampling

Water testing is an integral part of any legionella prevention programme and is essential for keeping building occupants safe.

Celtic Water Solutions offers comprehensive legionella testing and water safety risk management solutions to support businesses and those responsible for the safety of engineered water systems in the workplace.

Our water safety experts can help you manage your water systems, maintain regulatory compliance and so keep people safe.

Contact our team of legionella consultants to get the best advice.

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