Legionnaires’ disease is a potentially fatal form of pneumonia.

The risk of infection increases with age but some people are at higher risk including:

  • people over 45 years of age
  • smokers and heavy drinkers
  • people suffering from chronic respiratory or kidney disease
  • diabetes, lung and heart disease
  • anyone with an impaired immune system

The bacterium Legionella pneumophila and related bacteria are common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers.
They may also be found in purpose built water systems such as domestic hot and cold water systems, spa pools and evaporative condensers.
If conditions are favourable, the bacteria may grow increasing the risks of Legionnaires’ disease and it is therefore important to control the risks by introducing appropriate measures.

Where does it come from?

Legionella bacteria are widespread in natural water systems, however, the conditions are rarely right for people to catch the disease from these sources.
Outbreaks of the illness occur from exposure to legionella growing in purpose built systems where water is maintained at a temperature high enough to encourage growth, e.g. hot and cold water systems, spa pools, cooling towers and evaporative condensers.

How do people get it?

People contract Legionnaires’ disease by inhaling small droplets of water (aerosols) suspended in the air containing the bacteria.
Certain conditions increase the risk from legionella if:

  • The water temperature in all or some parts of the system is between 20°C – 45°C
  • It is possible for breathable water droplets to be created and dispersed, e.g. aerosol created by shower heads, water outlets, spa baths
  • Water is stored and/or re-circulated
  • There are deposits that can support bacterial growth, e.g. rust, sludge, scale and organic matter
  • Outlets are used infrequently
  • The system contains dead ends or unused pipe work

Reducing the risk of Legionella

The risk of Legionella causing illness in small domestic properties is exceedingly low.

Possibly the biggest risk is when you have been away from the property for more than a week or so or there are additional taps, showers or toilets that are not used daily.

Good practice in this situation is simply:

  • Run the hot water taps for at least 60 seconds
  • Flush shower heads for a minimum of 60 seconds
  • Shower heads should be dismantled and cleaned of scale and debris every 3 – 6 months
  • Keep the hot water on your boiler system at a temperature of minimum 50°C – 60°C
  • Flush the toilet twice to circulate fresh water through the system and empty the cistern


Ensuring your safety

Owners and managers of private rented property have a legal duty of care to ensure that their tenants and visitors can use the property safely.
The Health & Safety Executive is the government body responsible for water hygiene and Legionnaires’ disease. Further advice and information can be viewed on their website. www.hse.gov.uk/legionnaires

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