Legionella warning for reopening businesses

Published: 24 March 2021

tap with running water

When water systems are restarted the bacteria can be released through outlets such as taps.

As Lockdown restrictions start to be lifted across the city, Derby City Council's Food and Safety Team are reminding businesses of the importance of continuing to manage and maintain the water systems within their business premises.

As many businesses have been temporarily closed due to the Coronavirus restrictions, commercial water systems have not been used.  This can lead to water becoming stagnant within the system and being stored at a temperature that encourages harmful bacteria such as legionella to grow.  When the system is used again, the bacteria will be released into the atmosphere and could result in future respiratory outbreaks such as Legionnaires disease.

What is Legionella?

Legionella is a type of bacteria normally found in water systems such as ponds and rivers. Normally these sources do not cause any harm.  The bacteria doesn't normally grow in purpose built water systems that are well maintained as the water is constantly moving and the water is kept either hot or cold. 

When the system is not being used this can cause water to become stagnant for long periods of time and there is no control over the temperature of the water which can provide the ideal conditions for the bacteria to go.  When the system is used again the bacteria is pushed through the system and can be released into the air via aerosols (tiny water droplets) through water outlets such as showers, taps and by flushing the toilet.  If the bacteria is inhaled it can cause respiratory illnesses such as Legionnaires Disease, a potentially fatal form of pneumonia.

What can I do to prevent Legionella forming?

Where possible you should continue to keep your water system operating as normal.  Water outlets should be flushed regularly at least once a week to prevent any water from stagnating.  Hot water should be kept hot (above 60oC  so that it reaches a temperature of 50oC within one minute at the outlets, 55oC within in healthcare premises) and cold water cold (below 20oC).  The system should not be drained as this could leave stagnant water.

Where businesses are unable to keep their water system operational, the water system must be treated like a new system before it is used for the first time.  This means the system must be flushed through as well as be cleaned and disinfected.

Further guidance and advice in relation to legionella control is available from the Health and Safety Executives website, or from the Council's Health and Safety website.

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