Controlling legionella risk and exposure

The primary method used to control the risk from legionella is water temperature control. Water services should be operated at temperatures that prevent legionella growth:

• Hot water storage cylinders (calorifiers) should store water at 60°C or higher
• Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified)
• Cold water should be stored and distributed below 20°C
• A competent person should routinely check, inspect and clean the system, in accordance with the risk assessment.

Where the risk assessment shows that there is a reasonably foreseeable risk of exposure to legionella bacteria, the use of water systems, parts of water systems or systems of work that lead to exposure must be avoided so far as is reasonably practicable.

The congregation's Health and Safety representative may reasonably conclude that an external water treatment consultant may be required at this stage to take the necessary steps to obtain water samples for legionella analysis. This will determine the bacteria counts and the acceptable levels. Professional cleaning and sterilisation of the water system should then be carried out by professionals and retested to ensure acceptable levels have been restored.