H2O Hygiene water treatment industry news water graphic
Blogs and News

What is Legionnaires’ Disease & How to Prevent It

04 July 2022

Many organisations across the world understand that Legionnaires’ disease is something that needs to be taken seriously, but do you fully understand what exactly this dangerous disease is?

If you’re not sure, don’t worry – you’re not alone. Many people don’t fully understand Legionnaires’ disease, and without a good understanding of it, it can be hard to take the necessary steps to prevent it.

That’s why we’ve put together this quick rundown of Legionnaires’ disease – what is it, what causes it, what you can do to prevent it and how a water risk assessment will help.

What is Legionnaires’ disease?

Legionnaires’ disease (or legionellosis) is an acute type of pneumonia (an infection that inflames the lungs). It is caused when a bacterium called Legionella pneumophila is inhaled. This bacterium is often found in water systems, disused showerheads, taps, hot tubs and other environments where warm water is allowed to sit. 

It is severe enough that, if not treated, it can be fatal. People with compromised immune systems or pre-existing lung problems (such as those caused by smoking) are at a higher risk of death. 

What are the symptoms of Legionnaires’ disease?

After being exposed to the legionella bacteria, someone with the disease might notice the following symptoms:

  • Headaches
  • Muscle aches
  • A high fever of 40°C or higher


As the disease develops, you may start noticing symptoms such as:

  • A cough (which can bring up mucus and blood)
  • Chest pain
  • Unusual shortness of breath
  • Nausea, vomiting and diarrhoea 
  • Confusion/disorientation


Legionnaires’ disease can also affect other parts of the body, including the heart, but it primarily affects the lungs.

There’s also a milder form of the disease, called Pontiac fever, which produces mild fever, chills, aches and pains. These symptoms usually clear within a few days. 

Even if your symptoms are mild, get to your doctor and get it checked out – it could save your life!

What causes Legionnaires’ disease?

Legionnaires’ disease is caused by the Legionella pneumophila bacteria. This bacterium is usually found in low numbers in rivers, lakes and reservoirs, which means that you’re extremely unlikely to be exposed to Legionnaires’ while out and about in the wild.

However, many human-made environments just so happen to be the perfect breeding grounds for the bacteria – warm, wet and consistent. 

Where are legionella bacteria found?

Legionella pneumophila can be found in purpose-built water systems, especially ones where we keep the water at a regular temperature, such as:

  • Cooling towers
  • Evaporative condensers
  • Hot & cold water systems
  • Spa pools (jacuzzis, etc.)
  • Disused bathroom equipment (showerheads and taps especially)


Essentially, any place where water might sit at a consistent temperature can become a breeding ground for legionella, especially in areas that can support bacterial growth, such as containers that are rusted, or contain sludge, biofilm, organic matter or scale (this all can feed the bacteria). 

How does legionella bacteria cause disease?

While it is a waterborne bacterium, as it infects the lungs, it needs to be inhaled in order to cause symptoms (you can drink water that contains legionella bacteria and be absolutely fine!). 

This is why steamy showers, jacuzzis, air conditioning units and other systems that may spread water particulate are usually the culprits that cause Legionnaires’ disease; the bacteria is picked up and distributed in water vapour (aerosol), where we breathe it in and it infects our lungs. 

What are the treatments for Legionnaires’ disease?

Usually treated successfully by antibiotics, most cases of Legionnaires’ disease are relatively inconsequential (if treated ASAP). 

However, if contracted by a vulnerable person, or if left untreated, the disease can be fatal, so if you feel unwell, and suspect you may have the disease, get down to your doctor as soon as possible!

How to prevent Legionnaires’ disease

Legionella bacteria love stagnant water, which is why it’s important to:

  • Regularly flush your system (especially outlets that are used infrequently)
  • Remove any dead legs/dead ends in your pipe system
  • Conduct a weekly showerhead/hose clean
  • Periodically clean cold-water storage tanks
  • Drain hot water containers to check for any debris or corrosion (that can feed bacteria)


When installing a new system, it’s important to keep all pipework as direct as possible, insulate all pipes and tanks and fit tanks with lids and insect screens to protect against contamination. 

How to prevent Legionnaires’ disease in the home

Legionella bacteria are rarely found in the home, but it is still important to remain vigilant. 

Many cases of Legionnaires’ disease contracted at home are actually caught from moist potting mixes and gardening soils. That’s why we always recommend wearing gloves and a mask when handling these substances. 

Not only this, but if you’re lucky enough to have an air conditioning system at home for the summer months, it’s crucial that you carry out regular cleaning and maintenance in order to prevent bacteria build up.

Regularly flushing your systems is also important. If you have a shower that goes unused for extended periods of time, make sure to give the showerhead a clean and run it for a while every now and then.

Finally, if you have a jacuzzi or other spa system at home, it’s extremely important to keep it spotless and don’t allow water to pool for extended periods. 

Do I need a water risk assessment?

In the UK, any organisation, no matter if you’re big or small, is legally required to conduct a legionella risk assessment

They’re designed to keep you and the people living/working in your building safe, so it’s really important to get it right. 

We highly recommend talking to water risk assessment experts for bespoke advice on how you should proceed.

What is a water risk assessment?

A water risk assessment is when a professional water hygiene specialist surveys your entire system, checking every potential area of risk. They’ll produce a detailed schematic of your water system and will report on any immediate remedial work that you need to conduct in order to prevent Legionnaires’ disease and to remain compliant. 

By checking every nook and cranny of your water system, you can rest assured that your building’s water system is safe and secure for years to come. 

Water risk assessments, hygiene and remedial works from H2O Hygiene

At H2O Hygiene, we understand that water compliance is mandatory, but that doesn’t mean it needs to be dry.

We believe that your people deserve the highest quality water, that’s why we offer water risk assessments, hygiene services and other remedial works of the highest quality, carried out by our family of expert engineers and delivered with a smile. 

If you’ve got any questions at all about Legionnaires’ disease, water risk assessments, or anything else at all, don’t hesitate to give our specialists a call today. 

Want to learn more about what to ask a prospective water hygiene company? Click here to read about our 6 key questions to ask a water hygiene company before you sign a contract.

Ask Us a Question

Get in touch for more information

01922 666108

Contact us