Legionella is a type of bacteria that causes diseases like Pontiac and Lochgoilhead fever and in the worst case, Legionnaires’ disease.

Legionnaires’ disease

Legionnaires’ disease is a severe form of pneumonia and can be deadly. In 2019 alone, 503 cases of Legionnaires’ disease were reported/notified.


Who is at risk?

When it comes to Legionnaires’ disease, everyone’s susceptible. However, some people are more prone to infection – these are known as “at risk groups”:

  • People who are 45 years old or above;
  • Smokers and heavy drinkers;
  • Individuals with diabetes, lung and heart disease;
  • People suffering from chronic respiratory or kidney disease; or
  • Anyone who has an impaired immune system.
  • Men are also 3 times more susceptible than women.

Where do you find Legionella bacteria?

Legionella bacteria can be found in natural water supplies, like rivers, lakes, reservoirs and ponds, but usually in low numbers. Conditions are rarely favourable in these environments for transmission of the bacteria, and so natural water sources aren’t usually associated with Legionnaires’ disease.

More commonly, Legionnaires’ disease is linked to purpose-built water systems such as irrigation systems, spa pools, water features and hot and cold water systems, where conditions are favourable to support the growth of legionella bacteria.

The optimum temperature for Legionella growth is between 20-45°C. Temperatures lower than 20°C are generally too cool for the bacteria to multiply, while temperatures above 60°C are too hot for it to survive. Legionella bacteria also needs something to grow on like rust, sludge, scale and biofilms, which provide harbourage and food.

How is Legionnaires’ disease caught?

Legionnaires’ disease is caught by breathing in small droplets of water suspended in the air (known as aerosols) that contain the Legionella bacteria. 

Employees, visitors, customers, clients and anyone else in your premises run the risk of being exposed to contaminated, aerosolized water so it’s essential you have appropriate measures in place.

Your responsibilities

Duty holders (including employers) have a legal duty to identify sources and assess the risk of legionella.  To help discharge this duty, there there are a number of steps you can follow:

  1. Identifying and assessing risks

A competent person must carry out a thorough risk assessment to assess whether any of your water systems are likely to pose a Legionella hazard.

The assessor will look at the following points:

  • Does the water temperature sit between 20-45°C in any part of the water system(s)?
  • Is water stored and/or re-circulated in the system?
  • Are nutrients present for the bacteria to feed off?
  • Are any employees, visitors, residents, etc. at greater risk due to their age, habits or health condition?

The risk assessment will also help to prioritise the risks in terms of how harmful they could be, and consider who will be affected (remember, it’s not just employees… think about customers and visitors) as well as identifying suitable controls. 

  1. Manage the identified risks

You must appoint a “Responsible Person” to help manage legionella risk – this person should have a relevant level of training and understanding of legionella and your water systems to allow them to help control the risk of exposure. The Responsible Person will also be accountable for ensuring any contractors working on the water system are suitably competent.

     3. Prevent or control the risk

You should first consider if you can completely prevent the risk by changing equipment or processes.  

In reality, it may not be possible to completely prevent the risk so you will need to implement effective control methods.

For example, if you have cold water storage tanks on site, you should keep the water below 20ºC and you may need to install extra installation on the tank and pipework to prevent thermal gain.

If you need a hand working out what these are, get in touch with our Health & Safety experts.

  1. Accurate records

It is important to keep detailed records of your legionella controls. These are often kept in a Legionella logbook (as your written scheme of control) and would normally include:

  •  The significant findings of your risk assessment.
  • Written details of your controls and a monitoring scheme such as temperature testing, cleaning and sampling/testing (if required). 
  • Results of your monitoring scheme and an action plan if any issues are found.

Documentation should also include schematic diagrams of your water system and any details of the state of the system. 

Records should be retained for 5 years.

We’re here to help

When it comes to Legionella, there can be a lot to get your head around – which is where we come in. Our safety experts can help to identify any legionella risks within your business, conduct a legionella risk assessment and provide advice on simple in-house measures to reduce the risk.