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When Should Water Be Tested for Legionella Bacteria?

Legionella bacteria testing is usually one of the tests conducted as part of the management of a man-made water system. So, are you wondering whether the law requires you to test for Legionella bacteria in your hot and cold, and other water systems?

Ideally, you may not need to do this except under certain circumstances that may require mandatory legionella testing. However, if you are responsible for the management of water systems, you are required by law to manage the risks associated with the presence of Legionella.

An important part of your risk management strategy is the consistent testing and examination of the water in the systems you operate. So, how often should you do these tests? Here is a detailed guide to help you:

HSE Guide on Tests for Legionella

There are a number of circumstances identified by the UK’s Health and Safety Executive (HSE) on when to carry-out testing for legionella bacteria. Whilst there is no specific time period for renewing a Legionella risk assessment, most experts suggest that it should be updated at least after every two years unless there have been key changes, which would call for more frequent updates.

Nevertheless, you may need to do this quite often based on what is happening in and around the water system. As a result, there are a number of situations that may require you to update your assessment and perhaps carry out tests for Legionella in your water:

  • When changes such as pipe-work and other assets are effected on the water system.
  • When doubts arise over the disinfectant concentration in the water system that could show an absence of control.
  • At times when the water system or building itself undergoes a change of use.
  • When the population in the region falls within the category considered high-risk. For example, the elderly or those having an impaired immune system.
  • Where the management put in place to treat the water system is considered inefficient.
  • When you never attain the ideal temperatures for both your cold and hot water.
  • When for other reasons the situation is considered high-risk.
  • When positive Legionella samples are recorded or an outbreak of Legionnaires’ disease is suspected.

 Conducting Legionella Tests

Microbiological sampling of water is recommended to test for the presence of bacteria that could include the determination of dangerous levels of Legionella pneumophila. This is particularly important when there is a suspected outbreak of Legionnaires’ disease or when the control measures put in place are considered ineffective.

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This should be done in collaboration with water hygiene specialists such as Legionella Control International to determine the most appropriate remedial or disinfection works that could for instance include cleaning and chlorination of the water systems.

The testing for Legionella bacteria should always be conducted by a technically expert, UKAS accredited laboratory who are familiar with Legionella testing. However, all building and business owners (called duty holders) should assess and examine their respective water systems for the conditions favorable to the development of Legionella bacteria.

Conventionally, those responsible for the management and control of Legionella should work to a schedule of activities accompanied by a set of pro-active procedures for regular water tests of the system that would help to identify evidence of bacterial grow before it becomes problematic.

Recommended Frequency for Legionella Bacteria Tests

When you are not sure whether your existing control procedures are working as required, weekly tests for legionella should be performed over a specified time period to identify any trends, but also to confirm when the system is back under full control and so safe.

After having established that the system is safe, you can them carry-out monthly tests to help demonstrate that control of the water system has been achieved and is being maintained.

Cooling towers present a particular risk and so should also be tested regularly due to their increased risk. The cooling tower water and the make-up water should be tested for both legionella bacteria and microbial activity. Legionella bacteria testing for cooling towers must be at least after every three months unless there are issues that may warrant more frequent tests.

Such requirements are identified in the HSE’s ACOP L8 and the health and safety technical guidance HSG274 Part 1 guidelines. In the UK these are requirements set out in law and require that you follow the recommended testing frequencies.

The risk assessment identifies assets and pipe-work such as showers, taps and water tanks that form the water system. The risks linked with each element are also evaluated to determine their risk rating.

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Important Facts to Consider

It is important to note that the frequency of legionella testing varies based on the water system type, the existing assets, and associated risks and finally on the control and monitoring measures already put in place.

The monthly procedures required for monitoring hot and cold water temperatures are one of the most effective ways of confirming that the thermal control measures put in place are effective. Legionella bacteria proliferate between 20°C and 45°C.

The optimum temperature for their development is 37°C. Therefore, it is important to check water temperatures regularly to identify the prevailing conditions and establish whether they will help legionella bacteria to thrive.

These monthly water temperature test results should be retained for reference and to demonstrate that suitable measures are in place to control the growth and proliferation of Legionella bacteria to the regulator.

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