Preventing Legionnaires outbreak after lockdown – Part 1


Part 1: Flushing the plumbing and heating system

<p>While many of us have slowly become accustomed to the life under lockdown, it can be easy to forget that at some point, lockdown will be lifted, and we will gradually start to regain a sense of normality.</p>

<p>So, when the lockdown does lift, not only do we need to continue taking precautions with social distancing, we’ll also need to be extremely careful about how we handle the re-opening of commercial and public-use buildings. Particularly, the hot water systems in our buildings could be at a risk of a potential outbreak of another serious illness – Legionnaires.</p>

<p>In this blog, we’ll answer some crucial questions around Legionnaires’ disease, the Legionella bacteria, and how an outbreak can be prevented.</p>

What is Legionnaires’ disease?

Legionnaires’ disease is a form of an unusual pneumonia caused by any type of Legionella bacteria. Also known as legionellosis, signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur.

You can catch Legionnaires’ disease by breathing in tiny droplets of water that contain Legionella bacteria. This bacteria grows in stagnant water supplies, and you are most likely to get the disease in places like hotels, hospitals or offices from the air conditioning systems, showers, taps and toilets.

Anyone can contract Legionnaires’ disease, but the elderly, smokers, heavy drinkers and those suffering from serious illnesses such as cancer, diabetes, chronic respiratory or kidney diseases are at a greater risk. An added danger is that the symptoms are very similar to those of COVID-19, so it is vital that they are not confused.

How does Legionella bacteria get into water supplies?

As per the Health and Safety Executive (HSE) website, “Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20°- 45°C. The bacteria are dormant below 20°C and do not survive above 60°C.”

Why are we at a greater risk of Legionella growth during lockdown?

As many buildings like bars, restaurants, hotels, pubs, bed & breakfasts, offices, leisure centres and more are shut during the lockdown, the plumbing and heating systems in these buildings are not being used or maintained.

This means that the water within these premises is stagnant, creating the ideal circumstances for Legionella bacteria to grow and multiply. Also, as the temperature rises with spring and summer on the way, there is an even greater likelihood that water within the pipework is at the ideal breeding temperature of 20°- 45°C.

Bathroom tap open

How to prevent Legionella outbreak after the lockdown?

To avoid a Legionnaires outbreak after the lockdown ends, we strongly advise that all plumbing and heating systems in buildings that have not been in use, are thermally flushed, and all the water is drained from the pipework and replenished.

To do this, you need to first run all the taps in the building to get rid of stagnant water. This must be done carefully, and we advise that you wear the appropriate PPE (personal protective equipment) to prevent the inhalation of water droplets that could contain Legionella bacteria.

After the pipework has been drained, run the hot water system again at above 70°C. This will ensure that any lingering Legionella bacteria is also killed.

You may also find advice on flushing a system with chlorine – however, this is not an overly effective solution. It can be quite costly, difficult to dose correctly, and may not completely eliminate the bacteria.

network of pipes

Preventing Legionella growth in future

For landlords, property owners and employers, you have a duty of care to maintain the plumbing and heating systems within buildings and to ensure a safe environment.

The CEO of the Association of Plumbing and Heating Contractors (APHC), John Thompson, warns: “Landlords and employers have a legal duty to assess and control the risk of exposure to Legionella bacteria. Risk assessments, precautionary actions and remedial work can be implemented to protect against Legionnaires’ disease. However, we believe the vast majority of landlords and employers are unaware of their legal duty and of the actions that need to be taken.”

To further safeguard water supplies after thermally flushing the system, you can install specialised valves such as thermostatic mixing valves (TMVs) and Anti-Legionella valves to prevent the water supplies from future contamination.

TMVs allow the hot water system to run at temperatures high enough to disinfect and kill Legionella, while preventing users from being scalded at the outlet. Meanwhile, Anti-Legionella valves are installed in an area where water stagnation is highly likely – such as expansion vessels. These vessels accumulate water from expansion within water supplies upon increase in temperature. However, they are a potential spot for Legionella growth. The Anti-Legionella valve creates turbulence within the vessel allowing the water to de-stagnate prior to reaching any outlets.

A final tip to avoiding water stagnation is to regularly conduct ‘hygiene flushes’ on pipework and water appliances in low-use areas.

man holding Easifit TMV

Ensuring a safe environment after lockdown

Eventually, when the lockdown is lifted and facilities start to re-open, it is crucial that we all do our bit to ensure that people are kept safe from any health hazards, and we take all measures to protect the NHS from being overwhelmed.

Legionnaires’ disease is one such example, which can be extremely dangerous, if not fatal, especially for people with underlying health conditions. Although the illness can be treated, with due care and proper maintenance of plumbing and heating systems, we can prevent it from happening in the first place.

At RWC, we are with you all the way during these extraordinary times. For any questions on how to thermally flush the water system, and which valves to install in an application to ensure safe delivery of water, get in touch with our team of experts who are happy to support and provide advice.

We will also be publishing a ‘Preventing Legionnaires outbreak: Part 2’ blog soon, with more advice on preventing Legionella in future. The blog will discuss best practices around installation, use and maintenance of TMVs and Anti-Legionella valves, so stay tuned.

For more information on our Reliance Valves brand, please visit

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View our high performance Anti-Legionella Valves that prevent Legionella from breeding in cold water systems. 

Lee Halstead Headshot

Lee Halstead

Technical Sales Engineer - JG Speedfit/Reliance/SharkBite & JG Underfloor

About the author

As a seasoned professional in plumbing and heating, having earned City and Guilds Plumbing Craft and Advanced Craft certifications in 1991, I have dedicated myself to mastering the craft.

For over two decades, I operated as a self-employed plumbing and heating engineer, serving both residential and new build sectors.

In 2015, I transitioned into the role of a Technical Sales Engineer with RWC. In this capacity, I have leveraged my extensive field experience and technical knowledge to provide invaluable support and build strong relationships with customers. As a spokesperson for RWC, I am thrilled to share my expertise and promote the cutting-edge products and services we offer in the plumbing and heating industry.