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The Impact of Cold Water Systems in Hot Weather

With the weather improving as we finally feel like its summer, it’s worth thinking about the impact hot weather can have on water systems and temperature monitoring.


Warm weather and hot summer holidays, quite naturally, see an increased use of many water applications. hot tubs, showers are in greater demand in the summer, swimming pools are visited more frequently, and hose pipes are pulled out of hibernation for a summer of use.

While many are enjoying the warmest summer for many years, duty holders and responsible persons must be aware of the heightened – and hidden – risk of Legionella in water sources and systems.

To be able to flourish, Legionella needs a temperature range from 20-45°C – so the warmer weather is creating an ideal environment for the bacteria to grow and multiply. Temperatures in the UK this are predicted to go above and beyond 30°C, providing Legionella bacteria with warmer water systems to grow in.

Control measures for safer water systems

With hotter weather often seeing an increased risk of Legionella proliferation, there are a number of precautions to take to ensure that you minimise the risk of cases of Legionnaires’ disease, ensuring that you are compliant with HSE’s ACoP L8.

For hot and cold water systems, controlling the temperatures to ensure the water is outside of the Legionella growth band is vital. Keep all hot water systems at above 60C, with water outlets maintained at a minimum of 50C; in healthcare environments, this should be 55C. Likewise, cold water should be kept below 20C, wherever possible. That is not to say that Legionella is not a risk in the winter months, but water below 20C will mean the Legionella bacteria are dormant.

Compliance all year round

Taking steps to keeping your water systems safe should be done in line with a Legionella risk assessment. It’s not just advisory; if you are an employer or in control of premises, you are responsible for understanding the health risks of Legionella. Failure to risk assess water systems for Legionella is punishable by fine and a prison sentence. More often than not, when outbreaks occur, there is a serious risk to human health often resulting in fatalities.

Under the HSE’s Legionnaires’ disease: The control of legionella bacteria in water systems  Approved Code of Practice (ACoP) L8, those responsible for health and safety must adhere to the guidance and recommendations to identify and manage the risk of Legionella in all artificial water systems.


If you require support in managing Legionella, conducting your Legionella risk assessments or want general advice on what to do, please get in touch info@legionellaandfiresafe.co.uk or calling 0800 080 3045.


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