Legionellosis Prevention

Legionellosis is a collective term for diseases caused by legionella bacteria, including the most serious Legionnaire’s disease. In most premises the risk is low but there are some instances where they are increased. Read our guide for how to spot these instances and manage the risks.

What is Legionellosis?

Legionellosis is a collective term for diseases caused by legionella bacteria. The most serious of these diseases is Legionnaire’s disease, a potentially fatal form of pneumonia. Legionnaire’s disease is contracted by inhaling small droplets of water (aerosols) suspended in the air which contain the bacteria. 

The risk of contracting Legionnaire’s disease increases with age, amongst smokers, anyone suffering from chronic respiratory or kidney disease or with an impaired immune system. Risks can also increase in buildings using air conditioners or humidifiers, buildings with dead end pipes, long runs of pipework containing warm water, or indoor ornamental fountains and showers.

Legal requirements

There may be a range of health and safety laws that apply to your organisation including the Control of Substances Hazardous to Health Regulations. 
Requirements under these laws might include:
  • Complete, record and revise risk assessments to identify where precautions are required
  • Eliminate any hazardous substances that are present if possible
  • Implement suitable precautions to be taken where hazardous substances are present
  • Ensure precautions are taken and properly maintained
  • Provide information and training to employees, volunteers, and contractors

Example hazards

  • Water stored or re-circulated as part of the water system
  • Water temperatures between 20-45ºC
  • Sources of nutrients such as rust, sludge, scale, and organic matter that encourage bacterial growth
  • Water droplets being produced and dispersed over a wide area
  • Employees, volunteers, and visitors who are more susceptible to infection
  • The use of humidifiers and air-conditioners


Here are some examples of precautions you can take:
  • Avoid water temperatures and conditions that flavour the growth of legionella
  • Ensure that the release of water spray is properly controlled
  • Make sure water cannot stagnate anywhere in the system
  • Keep the water and water system clean
  • Treat water to control the growth of legionella
  • Arrange for air-conditioners and humidifiers to be cleaned and serviced regularly
  • De-scale shower heads and running showers periodically

Making a start on your legionella risk-assessment

1. Identify and assess the risk from legionella bacteria at your premises

2. Implement any additional precautions that might be necessary

3. Train those employees or volunteers with specific roles relating to your water systems

4. Record all actions you have taken

5. Document your arrangements and responsibilities for legionella