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Legionnaires Disease

Legionnaires Disease – Guidance Note for tenants and residents of rented domestic accommodation

Legionnaires’ disease is a potentially fatal form of pneumonia caused by legionella bacteria. Legionella bacteria can multiply in hot or cold water systems, and is transmitted by aerosol, eg in spray from showers and taps.

Legionnaires DiseaseLegionella bacterium remains dormant at low temperatures. It thrives at temperatures in the range 20 degrees C – 45 degrees C. The bacteria is killed at temperatures in excess of 60 degrees C.

Maintaining cold water temperatures below 20 degrees C and hot water temperatures above 60 degrees C (cylinder), or 50 degrees C (outlets) is a simple and effective means of preventing the proliferation of legionella bacteria within the system.

Standing / stagnating water encourages ideal conditions for bacteria to develop, in addition, scale, debris and bio-film provide nutrient for the bacteria to flourish.

Ensuring that water is regularly moving throughout a system and that the showers, taps and other outlets are free from scale and regularly cleaned, reduces the risk of bacteria developing.

As a minimum you MUST:

• Ensure that water is regularly circulated throughout your system, do not leave areas where water is stored for lengthy periods of non-use.
• Flush infrequently used outlets weekly.
• Maintain the temperature of water at the outlets below 20 degrees C for cold and above 50 degrees C for hot.
• Run the hot water taps (a very unlikely source anyway) for a minimum of 60 seconds
• Shower heads should be dismantled and cleaned of scale and debris every 3-6 months.
• Clean and de-scale, where necessary, all outlets regularly
• Flush the toilet twice to circulate fresh water through the system and empty the cistern.


• Interfere / adjust the temperature controls of your boiler.

Where systems are left unused for lengthy periods of time (Holidays etc), the taps and showers must be flushed through until the above hot and cold temperatures are achieved without generating an aerosol spray.

Ideally these should be left to run at the required temperatures until any stored water in the system is used up. Outlets should be cleaned and disinfected.


Category : Advice



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