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Why Temperature Monitoring is important for Legionella Compliance.

Temperature monitoring and control is most commonly used as the primary method of controlling Legionella bacteria in hot and cold water systems. Although other factors can affect the presence and proliferation of Legionella bacteria, temperature control plays a pivotal role in understanding and managing the risk.


Legionella thrive in certain temperatures, more specifically in temperatures between 20°C - 45°C. Water systems running outside this temperature range lowers the risk of the bacteria proliferating drastically. The bacteria will start to diminish within 2 hours at 50°C, within 2 minutes at 60°C and immediately at 70°C - although this creates a scald risk. Legionella can survive in temperatures under 20°C, however it will be inactive.


Temperature monitoring is important as it acts as a regular assessment of the environment and whether it is comfortable for Legionella bacteria. If the temperature of an outlet falls within the range, then it increases the chance of the bacteria being present within the water system. With this information, the site responsible person can react and adjust the temperatures accordingly, therefore lowering the risk. Temperature monitoring acts as a prevention measure, and adjusting the temperatures act as a reactive measure.


How to react to non-compliant temperatures will be dependent on the situation and the water system. As a minimum, the responsible person should be made aware and they should investigate further, if adjusting the temperature has not solved the issue.


All temperature monitoring should be recorded and kept within the logbook system, whether this is kept digitally or onsite. As per the HSE’s guidance (HSG 274 Part 2), records should be kept for a minimum of 5 years.


The regularity of temperature monitoring should be part of your control programme, written scheme of control and highlighted within your Legionella Risk Assessment. Following the guidance set out by the HSE within the HSG 274 Part 2 (Table 2.1), sentinel outlets are recommended to be monitored monthly and all other outlets to be tested on a rotational basis, at least once annually. Sentinel outlets are those that are the ‘nearest’ and the ‘furthest’ outlets connected to each water system. Calorifiers and combination water heaters should also be checked monthly, whereas POU water heaters are determined by your risk assessment. CWSTs should be temperature checked 6 monthly.


Please see below for an overview of compliant temperatures:


Cold Water

Cold Water should be stored and distributed at below 20°C, whether the system is fed via mains or a Cold Water Storage Tank (CWST).

CWSTs should also be sufficiently insulated to reduce the risk of ambient temperatures during summer months. CWSTs should be temperature checked on a 6 monthly basis, including ideally during the summer months.


Hot Water

Hot Water should be distributed to the outlet at 50°C minimally. Within Healthcare settings, this would need to be 55°C.

Calorifiers and Hot Water Cylinders flow temperature should be above 60°C and the return should be no lower than 50°C.

POU Water Heaters (15 litres) need to have temperatures between 50°C - 60°C. In a Healthcare setting, this needs to be 55°C.

Combination Water Heaters should also be between 50°C - 60°C.


For further advise on temperature control, management programme or written scheme of control, please contact us on 01296 914916 or click the 'Let's Talk' button below.




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