Legionella bacteria, which are responsible for Legionnaires' disease, can be widely found in nature, especially in bodies of water. Despite new treatment methods, some bacteria survive and find their way into the local water systems. And when favourable conditions are present, the population of the bacteria can burgeon and lead to an outbreak of Legionnaires' disease.

There are several strategies that can be implemented to control the population of Legionella. The most common way to control the population of the bacteria is through water temperature control which renders the water unsuitable for the microorganism. Legionella thrive in a temperature range between 20°C and 45°C.

Another way to control the population of Legionella is routine flushing of stored water. Chemicals especially formulated to control bacteria population may also be used.
Now, if you have been tasked to oversee the management of a water system, one important question you are probably asking pertains to Legionella testing frequency.

In the past, the recommended testing frequency was every two years. However, due to new regulations released by the UK authorities, the emphasis has shifted toward performing Legionella risk assessment on a regular basis. The results of this assessment, in turn, will serve as a guide as to how often testing should be done. A thorough Legionella risk assessment should include various components of the pipework including showers, taps and water tanks.

In most circumstances, testing water systems for Legionella every two years is advisable. However, there are instances wherein an immediate test is recommended. Have the water system checked when the majority of the residents in the property you are managing fall within the high risk group, which includes the elderly.

If the use of the water system has been significantly changed or work has been done on the pipework or some of its components, it is crucial to perform a test. Have the water tested for Legionella immediately if you suspect that there is a Legionnaires' disease outbreak.

The frequency of Legionella testing will depend on several factors including the pipework and its components and the control and monitoring measures that you are currently using.
But on top of testing, it is also imperative to note the importance of monitoring the temperature of the water system. Changes in temperature in water systems can increase the risk for the growth in population of the Legionella bacteria.

Also, remember to record the results of all tests and monitoring that can prove invaluable should there be a suspected outbreak.

Written by +Duncan Hollis, Aquacert