legionella risk assessment

Legionella Risk Assessment

Legionella is a bacterium found in aquatic habitats. Its natural habitats are lakes, streams, or rivers but it can also grow and spread in man-made building water systems such as hot tubs, shower heads, spa pools, etc.

Although the bacterium might not pose any threat in its natural habitat, when it finds its way into a man-made water system, it becomes a threat to humans and can cause health issues like legionnaires disease.

That is why business owners and house owners are compelled by the law to carry out a proper legionella risk assessment to mitigate the risk of an outbreak of legionnaires disease. This is to ensure the safety of everyone within the walls of a building.

This article will cover the risk associated with legionella, the importance of legionella risk assessment, and how it’s done.

Let’s get right into it!

What is Legionnaires’ disease?

Legionnaires disease is commonly associated with legionella. It is a severe kind of pneumonia that is caused by the infection of legionella bacteria. The disease is contracted by inhaling water droplets that contain this bacteria.

The disease usually develops 2 to 10 days after being exposed to legionella. Symptoms of legionnaires disease may include:

  • Chest pain
  • Headache
  • Shortness of breath
  • Cough
  • Fever

If it is not treated fast, severe complications may result in some life-threatening conditions such as respiratory failure, acute kidney failure, septic shock, etc.

Why is Legionella Risk Assessment Important?

Legionella risk assessment is important for safeguarding the lives of everyone who comes near a building. As a business owner, it is important to ensure that anyone who comes into your building is safe.

Here are some other reasons why legionella risk assessment is important:

Helps prevent legionnaire’s diseases

Legionnaires disease is the most fatal illness associated with legionella. The risk assessment is important to help prevent the disease and other diseases associated with legionella.

Doing regular legionella risk assessments will prevent the water system to be contaminated and if contaminated, can be treated before people start inhaling the contaminated aerosols and contracting legionnaires.

Compliance with the law

The legionella risk assessment is mandatory for every business owner according to the law. The violation of this health law may attract penalties from the body in charge.

The duties and obligations of owners of buildings on how to reduce and prevent the exposure of legionella to their environment are listed under The Health and Safety at Work Act 1974 (HSWA). The duties include:

  • They have to flush hot and cold taps for two minutes
  • Monitor the temperature of their water regularly
  • Carry out legionella testing and monitoring, record the results and retain them for at least five years.

Also, the Health and Safety Executive has laid out practical guidelines and legal requirements for duty holders on how to control and minimize legionella bacteria in the water system. As a business owner, you’re a duty holder under the law, and you’re in charge of assessing the risks in your water system.

Safety of employees and clients

Legionella risk assessment is also important because it helps to protect the health and well-being of your employees and clients and any other visitors coming to your business environment.

The assessment will help you prevent the water system from getting contaminated and if already contaminated, you’ll find out and know how it can be treated.

How to carry out a legionella risk assessment

We’d advise you to employ a water-cleaning company to carry out the legionella risk assessment for you because of their competency and experience. But it’d still be good to have basic knowledge of how it is done.

Step 1: Consider who may be at risk

The first step is to check who is at more risk of getting infected by the bacteria. The purpose of this is to make sure you know who should get tested first for legionnaires disease in case legionella bacteria is found in the water systems.

To do this, you’ll need to make a list of all the people present in the building and mark out people who are at more risk than others due to age, weak immune system, smoking, underlying illness, etc.

Step 2: Pinpoint potential risks

When carrying out a legionella risk assessment, the first thing you should do is locate sources of risks in the building. You can create a list of all the available water systems in the building and assess them one by one. According to HSE, you need to check:

  • If water is being recirculated or stored in your water system.
  • If the water temperature in the water systems is between 20 – 25 degrees.
  • If there are sources of nutrients such as rust, organic matter, sludge, etc for the legionella to grow.
  • If water droplets could be dispersed and which area they would be dispersed over.
  • If there are people in the building who are more prone to contract legionella infection due to age or underlying illness.

All items on this list have to be checked to determine if there is currently a risk of legionella. If there is not, you should check if there is the possibility of any risk shortly.

Step 3: Implement safety measures

Whether or not there is a potential legionella risk, it is important to carry out safety measures to control or prevent the bacteria from growing in your water systems.

Before you can implement a safety measure, you need to know the factors that make your building prone to legionella bacteria. And here are some of them:

  • Lukewarm water temperature
  • Infected cold water storage
  • Unnecessary piping and dead legs

To keep your water system legionella-free, here are some safety measures you should take:

  • Ensure hot water is stored above 60 degrees celsius.
  • Get rid of dead legs and redundant pipeworks.
  • Flush out water systems regularly to remove stagnant water that can harbor legionella.
  • Clean the outer parts of the water systems such as showerheads, baths, and tubs regularly.
  • Do regular inspections of the water systems, like monitoring water temperature.

Step 4: Record your legionella risk assessment

You need to make sure you document and record your risk assessment procedures. This is to help prove to relevant authorities that you’ve complied with the legionella risk assessment law and to show you’ve safeguarded the health of your workers and customers.


Legionella is a very harmful bacteria that can cause lung infection which could result in a more complicated health issue. Legionella risk assessment is the statutory responsibility of every building owner to safeguard the health of anyone that comes in contact with their property.

Employ a reputable water cleaning company to take charge of the treatment and monitoring of the water system in your business environment and make arrangements to review the assessment from time to time.