Understanding Legionella: Everything You Need to Know

Legionella is a bacteria found in water that can lead to serious issues for human health if contracted, with Legionnaires’ disease being a potentially fatal type of pneumonia. Anyone can contract this deadly disease, with some more than others being more susceptible to it.

Controlling Legionella bacteria is crucial in domestic water systems and even more so in commercial systems to ensure the safety of public health. Not many people are aware of the measures required to minimise the risk of Legionella bacteria being present in their water systems, reducing the risk of catching the disease.

WaterCare Solutions is here to help you understand the fundamentals of Legionella, the disease and its symptoms, where it’s most likely to be found and the Legionella risk assessment guidelines.

Legionnaires’ disease

Legionnaires’ disease should not be taken lightly. The disease can cause serious health issues and can be fatal, unless those with it seek medical attention, sooner rather than later. The disease mainly attacks the lungs and can be contracted by breathing in tiny droplets, aerosols, or vapour, of water containing the bacteria. There are over 40 individual known species of Legionella, with the most common type infecting humans being Legionella pneumophila.

The collective term for diseases caused by Legionella bacteria is known as Legionellosis, including the highly serious Legionnaires’ disease. Pontiac fever is a less serious form of Legionellosis, which involves flu-like symptoms lasting up to 2-5 days. What separates Legionnaires’ disease from Pontiac fever is Legionnaires’ can lead to a fatal illness involving pneumonia.

Where is Legionella most likely to be found?

Legionella bacteria are present in natural water systems, such as rivers and ponds, but do not have the right conditions for people to catch the disease from them. Legionella bacteria becomes more dangerous and concerning in man-made, purpose-built systems, including water towers, hot and cold-water systems, evaporator condensers, air conditioning systems, and spa pools and hot tubs.

Green algae and stones in the river floor

This is due to several reasons, as these water systems will be maintained at a temperature that facilitates the growth of the bacteria. Plumbing systems with stagnant water or water outlets that are not in frequent use also increase the chances of the bacteria growing.

Larger locations are typically more vulnerable to catching the virus than domestic properties are. The bacteria grows and spreads in certain places, such as hotels, hospitals and workplaces, where it enters the tainted water system of the building. Larger structures allow the bacteria greater space to grow and disperse.

What are the symptoms of Legionnaires’ disease?

Pneumonia-like symptoms

The symptoms of Legionnaires’ disease are hard to miss. Once infected, the symptoms will typically begin to show within two to ten days, with this Pneumonic type of sickness causing a high temperature, fever and chills, a dry cough, muscle pains, headaches, diarrhea and even confusion. Some of those infected may also experience coughing up blood or greenish bile if left untreated.

However, further complications will arise including respiratory failure as the lungs are failing to give out enough oxygen to the whole body, septic shock due to vital organs not receiving enough blood, and kidney failure due to the kidneys not being able to filter waste.

If you are experiencing any of these symptoms, you should seek Medical Help Immediately.

What type of conditions promote the growth of Legionella bacteria

So, we know where Legionella bacteria is found, but what encourages the growth and spread of this harmful bacteria? Here’s our list of the conditions that promote the growth of Legionella bacteria:

  • Water temperatures between 20-50°C.
  • Locations where there is an established source of sludge, organic matter, algae, scale, and rust.
  • Bio-film on water surfaces
  • Poor water management
  • Inefficient training programmes for staff in commercial sectors like hospitals, care homes, hotels, etc.

There are also external factors effecting the growth of the bacteria, including:

  • Water stagnation
  • Changes in municipal water quality
  • pH fluctuations
  • Poor levels of disinfectant
  • Water temperature fluctuations

Who is most at risk of Legionella?

Anyone can be at risk of suffering from Legionnaires’ disease but like most diseases and infections, certain parameters can greatly put people at a higher risk. With age comes a greater risk, as people over the age of 45 will be more susceptible to infection.

As Legionnaires’ disease mainly attacks the lungs and other vital organs, including the liver and kidneys, heavy smokers and drinkers are not only more at risk of contracting it, but symptoms will develop faster and more severely.

Those with a weakened immune system due to being sick for a very long time from illnesses like Cancer, conditions such as Diabetes and even a person’s poor diet can increase the risk of this terrible and often fatal infection.

sick middle aged man coughing. sitting at his apartment from drinking legionella infected water

Transmission methods

Fortunately, research has shown Legionella is not transmitted from human-to-human or animal-to-human contact and is only transmitted from the environment to humans. In fact, there are no reports of animals being naturally infected by the Legionella bacteria.

Potable water is the most common source of Legionella, but it is mostly harmless when drank directly – when humans inhale contaminated aerosols or when warm water droplets make their way to the lungs through aspiration, the bacteria can spread, causing the symptoms associated with the disease.

Is a Legionella risk assessment a legal requirement in the UK?

It is a legal requirement for landlords, employers and building managers to perform a Legionella water safety assessment. This goes for all offices, hotels, domestic residences, care homes, hospitals and any commercial building you can think of.

The Health and Safety Work Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) require landlords and employers to assess the risk of exposure and implement and manage precautions to control the risk of Legionella bacteria in water systems.

Non-compliance with these regulations can result in fines and prosecution. It is crucial for those responsible for managing premises and water systems to ensure the health and safety of occupants and users of the facilities. Not complying with these laws or adhering to Legionella water testing and safety can be devastating for businesses, with a fatal case of Legionnaires’ disease hitting an Essex Bupa care home resulting in a £3 million fine.

The Legionella risk assessment guidelines are as follows:

  • Perform a risk assessment to identify any potential problems of Legionella contamination in the water system.
  • If any risks are found, implement the necessary control measures.
  • Provide frequent maintenance of the water systems to ensure they are in good working order as well as regularly inspection and testing.
  • Keep records of risk assessments, inspections and maintenance activities.
  • Appoint a designated person to carry out these tasks and ensure the water system is safe.
Wooden Gavel With Golden Scale On Table

How often do I need a Legionella risk assessment?

A Legionella Risk Assessment should be performed on the initial installation of the water system in use. After this, ongoing risk assessments must be carried out annually and control measures must be in place. Also, any changes to the water system or building use, such as renovations, will require a risk assessment. Of course, a Legionella water safety assessment must happen immediately if there is a case of Legionnaires’ disease associated with the building.

A risk assessment has no fixed period for the validity, but regular monitoring and management of water systems is vital, with any issues being identified and controlled efficiently.

What is the best way to treat Legionella?

If you are ever unsure of how to carry out a Legionella risk assessment, the experts at WaterCare Solutions provide practical advice and guidance to duty holders to meet their legal requirements. Not only can we guide you, but our action plan will eliminate Legionella bacteria from your water systems, increasing the safety for all. Our Testimonials speak for themselves, with our clients more than happy with the Legionella risk assessment and control measures we provided.

If you need effective, bespoke and efficient Legionella risk evaluations for your water systems, get in touch with us today on 01299 271144 or contact us via email at mark@watercaresolutions.co.uk. We are more than capable of assessing all types of commercial, industrial and domestic water systems.


It typically takes two to ten days after exposure to the bacteria, but, depending on the type of bacteria you contract, the symptoms could show around five to six days post-exposure 

While Legionella bacteria can form and multiply during any time of the year, Legionella is more common in the summer as it thrives in warmer environments. 

There are several means for preventing Legionella bacteria in your boiler, including:

  • Service your boiler regularly with qualified professionals
  • Inspect the system for signs of corrosion, scale and biofilm
  • Maintain hot water at a temperature high enough to stop the growth of Legionella (above 60°C)
  • Ensure cold water is stored and distributed at temperatures below 20°C
  • Avoid stagnation by regularly using all water outlets and regularly flush ones that are not used frequently
  • Disinfect the boiler with professional help with disinfectants like chlorine

Legionella bacteria can survive in a plumbing system for several weeks or even months, depending on the temperature of the system, if there is a presence of biofilm, if any areas have stagnant water or if there is an absence of disinfectants.

The risk is generally low of getting Legionella from a Combi boiler, as these heat water directly from the mains as it is used, so there is no water storage for the bacteria to multiply. Always ensure the temperature of the water produced is above 60°C so the bacteria can’t survive.

While boiling water is effective at killing Legionella bacteria and can help prevent the disease, this practice is not sufficient for large water systems, such as those in buildings and homes, but can be used for drinking water.

While it is generally safe to wash your hands if the water is contaminated with bacteria, it is crucial to avoid creating vapours or aerosols which can be inhaled, which is how the disease is spread to humans.

The process for cleaning a shower that has Legionella bacteria on it or running through it involves cleaning and disinfecting the shower head frequently with products designed to kill bacteria. These could be chlorine-based disinfectants or home remedies such as baking soda with white vinegar.

Running hot water that’s 60°C and above throughout the shower system will kill any Legionella bacteria present. Also, consider hiring professional cleaners to disinfect the system if there is a known contaminant.

Showering can create water aerosols that, if contaminated with Legionella, may be inhaled, leading to possible infection. Regularly cleaning and disinfecting the shower system, as well as ensuring you’re running your water at 60°C or above, will help manage the growth of Legionella bacteria.

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