Tom Melhuish 8 min read

Legionella detection and prevention for businesses

Legionella is a common but deadly pathogen that grows in stagnating water systems in as little as a few weeks or months.

Inhaling airborne Legionella from aerosols can result in severe pneumonia, so UK businesses must prevent and protect their workforce and customers from exposure.

This guide examines Legionella, what it is, where it grows, and how to implement a prevention and detection program.

💡 Key contents

What is Legionella?

Legionella is a water-borne bacteria that causes a severe type of Pneumonia called Legionnaires’ disease when inhaled through contaminated aerosols.

It can grow in any place where water stagnates for long periods at room or warm temperatures.

Legionella-borne water must be disturbed and aerosolised to spread and cause infections, as it must be inhaled to be dangerous.

💡 Drinking water contaminated with Legionella is usually considered safe, but since it is associated with stagnating water, it may contain other pathogens.

Legionnaires’ disease

Legionnaires pneumonia must be taken seriously as it may require hospitalisation for the infected and can be fatal if not treated promptly, especially in vulnerable populations such as the elderly or the sick.

It is no joke: five hundred people in England catch Legionnaire’s disease every year, killing around one in ten!

While infection is uncommon, it is most typical in hotel guests, hospital patients, elderly in care homes, employees at poorly maintained office buildings, construction work, and public facilities with high amounts of water aerosols such as spas and swimming pools.

Ideal conditions for Legionella growth

Legionella bacteria love water stagnation, warmth and protection. They thrive in unoccupied water systems, typically indoors and in summer. Here are the details:

TemperatureOptimal growth occurs between 20°C and 45°C, which include both water at room temprature and heated water.
Stagnant WaterStagnation promotes biofilm formation, which protects bacteria from disinfectants.
Nutrient AvailabilityOrganic matter, scale, and sediment provide nutrients for growth.
Biofilm PresenceBiofilms offer a protective environment and nutrients.
pH LevelGrowth is favoured in water with a pH between 5.0 and 8.5 - a range in which British water infrastructure lies within.
SedimentSediment can harbour bacteria and provide nutrients.
Scale and CorrosionThese can protect bacteria from disinfectants and offer a nutrient source.
Aerosol GenerationSystems that generate aerosols, like showers and cooling towers, can spread bacteria.
Inadequate DisinfectionIneffective disinfection allows bacteria to survive and multiply.
Surface waterSurface water can have higher initial contamination, so any system that uses or disturbs this later is higher risk.

Places where Legionella grows and spreads

The perfect conditions for Legionella growth are found in many places in any building’s water systems, but not all of them necessarily create the aerosols needed for infection. Here is how Legionella growth, spread and infection occur in different components of a business’ water system:

ComponentsLegionella Growth? (Y/N)Airbourne Legionella spread? (Y/N)
AeratorsY - Can accumulate biofilmY - Aerosols generated during use can spread bacteria in the air
Centrally-installed MistersY - Warm, stagnant water in misters can support bacterial growthY - Mist generated can spread bacteria into the air
Cooling TowersY - Provides ideal warm, moist environments for bacterial growthY - Aerosols generated by the cooling towers can spread bacteria in the air
Decorative FountainsY - Warm, stagnant water can promote Legionella growthY - Aerosols generated by water spray can spread bacteria
Electronic and Manual TapsY - Warm water and biofilm formation support bacterial growthY - Aerosols generated during use can spread bacteria in the air
Expansion TanksY - Stagnant water can support bacterial growthN - No direct aerosolisation
HosesY - Stagnant water and biofilm formation support bacterial growthN - No direct aerosolisation
Hot and Cold Water Storage TanksY - Stagnant water and biofilm formation can promote bacterial growthN - No direct aerosolisation
Ice MachinesN - Cold temperatures do not support Legionella growthN - No direct aerosolisation; bacteria spread through melted ice water
Infrequently Used Equipment, incl. Eyewash StationsY - Stagnant water supports bacterial growthY - Potential for aerosolisation during use
Medical Devices (e.g., CPAP machines, hydrotherapy equipment, bronchoscopes)Y - Warm, stagnant water can support bacterial growthY - Aerosols generated during use can spread bacteria
Nonsteam Aerosol-generating HumidifiersY - Warm, stagnant water can support bacterial growthY - Mist generated can spread bacteria into the air
Pipes, Valves, and Water FittingsY - Stagnant water and biofilm formation support bacterial growthN - No direct aerosolisation
ShowerheadsY - Warm water and biofilm formation support bacterial growthY - Aerosols generated during use can spread bacteria in the air
Tap Flow RestrictorsY - Can accumulate biofilm and stagnant waterN - No direct aerosolisation
Water FiltersY - Can accumulate biofilmN - No direct aerosolisation
Water HeatersY - Warm temperatures (20-50°C) promote Legionella growthN - No direct aerosolisation
Water-hammer ArrestorsY - Stagnant water can support bacterial growthN - No direct aerosolisation

Historical Legionella outbreaks in the UK

Now that you understand the ideal conditions for legionella growth, spread and infection, here are some real-life UK case studies in which Legionella outbreaks have occurred:

Year (Click for Source)Location (Industry)Mechanism of OutbreakCases (Deaths)DescriptionConsequences
2002Barrow-in-Furness (Public building)Contaminated air conditioning system180 (7)Linked to the air conditioning system in a council-run arts centre.Barrow Borough Council fined £125,000; individual employees received fines and community service.
2003Hereford (Industrial)Contaminated cooling tower28 (2)Outbreak traced to an aerosol plume from a cooling tower at a vegetable packing plant.Company fined £100,000.
2006London (Leisure)Spa pool at a flower show3 (0)Cases linked to exposure at a spa pool display at the Chelsea Flower Show.No prosecutions; tighter controls at public events.
2012Edinburgh (Industrial)Contaminated cooling tower95 (4)Outbreak linked to industrial cooling towers in the city.Companies involved fined a total of £225,000.
2015Staffordshire (Healthcare)Hospital water system5 (1)Outbreak occurred in a hospital, traced to the water system.Hospital fined £200,000.
2017Stoke-on-Trent (Hotel)Spa pool3 (0)Linked to a spa pool in a hotel, affecting guests and staff.Hotel fined £75,000.
2019Braintree (Commercial)Contaminated water system in a supermarket9 (1)Outbreak linked to the water system in a supermarket.Tesco fined £8 million.
2020Bristol (Care home)Contaminated water system10 (2)Outbreak in a care home, affecting elderly residents.Care home fined £300,000; management received training.

Legionella regulations

‘Health and safety’ and ‘Hazardous Substances’ regulations tackle preventing and managing Legionella at business premises.

The most pertinent regulation is the Health and Safety Executive (HSE) Approved Code of Practice (ACoP) L8: “Legionnaires’ disease: The control of legionella bacteria in water systems”, which provides immediate practical advice and legal requirements.

According to this document, the key requirements for all UK businesses are as follows:

Key RequirementsDescription
Risk AssessmentIdentify and assess sources of risk, such as water systems that could harbour legionella bacteria. Should be conducted initially and reviewed at least annually, or whenever there are changes to the water system or its use. Applies to all businesses with water systems.
Control MeasuresImplement measures to control the risk of legionella, including water treatment and regular cleaning. Specific measures may include maintaining water temperatures outside the range of 20-45°C, regular flushing of outlets, and using biocides. Applicable to all businesses with water systems.
Monitoring and Record-KeepingRegularly monitor water systems and keep records of the control measures in place. Water temperature checks should be done monthly, with system inspections every 3 to 6 months. Applies to all businesses with water systems.
TrainingEnsure that staff are trained and aware of the risks and control measures related to legionella. Training should be refreshed at least annually, and whenever there are updates to procedures or personnel changes. Applies to all businesses with water systems.
Review and UpdatePeriodically review and update the risk assessment and control measures as necessary. Reviews should be conducted at least annually, and whenever there are significant changes to the water system, its use, or if there are any incidents. Applies to all businesses with water systems.

Compliance with Legionella regulations

The Health and Safety Executive, with the support of local authorities, is in charge of enforcing Legionella regulations on UK businesses. Non-compliance can lead to legal action, fines, business closure, and even imprisonment for severe breaches, leading to a significant outbreak. See our case studies for some examples!

Well-regulated industries such as the healthcare, hospitality, and industrial sectors generally show higher compliance rates, while smaller businesses often face challenges due to limited resources. Construction sites can also be at higher risk due to the temporary nature of their business water connections.

Legionella water management program

A water management program is essential for businesses seeking to ensure compliance with Legionella regulations.

It’s essentially a plan to implement risk assessments, control measures, monitoring, training and reviews to keep up with any regulation changes. Here is a step-by-step overview of how to get started:

1. Assemble a water management team

Assemble team “Anti-Legionella”, made up of representatives from facility management, engineering, maintenance, infection control (for healthcare facilities), and safety. Make sure the team is familiar with your specific water system and has ample technical knowledge.

2. Take a full inventory of your water system

The team’s first responsibility is to have a clear overview of the water system to identify key areas of concern as well as accessible areas to set up controls for monitoring, testing, etc.

This includes making flow diagrams of both potable and non-potable water systems, as well as portable water equipment such as hoses and pumps which are sometimes left out unchecked.

Here are some examples:

💡 Make sure every floor level is considered and any system that uses water has been listed.

3. Risk assessment, control, monitoring and training

Taking inventory is essentially like doing the heavy lifting. Your team of experts will intuitively have an idea of the riskiest components, where and how best to control them and where and how often to monitor the water system.

We cover each of these in more details in this table.

💡 It’s important for your staff to receive training, as they can help identify potential risks that were previously overlooked, such as stagnating water, and biofilms.

3b. Testing for Legionella

You will need to test your water supply for Legionella and other pathogens as part of your regular control measures and monitoring to ensure the safety of your employees, guests, patients, or contractors.

To test for Legionella, your experts will collect water samples from the designated control points. The detailed sampling and lab methodologies used are detailed in the Health and Safety guidelines in our regulations section.

4. Establish a Legionella emergency action plan

No matter how thorough your controls and monitoring, there is always a chance Legionella has entered and established somewhere in your water system.

Even changes outside your control like works in the mains pipes outside of your property can change your water pressure and send previously free flowing areas of your water system into stagnation for enough time for Legionella to form.

In any case, you need to establish both a:

  • Response plan: Create a clear plan of action for when Legionella is detected, including notification procedures and corrective measures.
  • Remediation steps: Outline specific steps to remediate contaminated systems, such as hyperchlorination or thermal disinfection.

5. Review and update your plan

Finally, you need to ensure your periodically review your entire Legionella setup and update it to incorporate new methods or technologies that could facilitate your job, such as smart monitoring and automated alerts.

6. Document and communicate all activities

Finally, document and communicate all of your water management procedures, as this is essential for proving compliance with regulations.

This includes written evidence of all the above steps.

Legionella detection and prevention for businesses – FAQs

Our business water experts answer commonly asked questions on Legionella detection and prevention for businesses in the UK.

How common is Legionella in the UK?

Legionella is relatively common in the UK, especially in the man-made water systems listed here. This includes cooling towers, hot and cold water systems, spas, and showerheads, just to name a few.

While exact prevalence rates can vary, following Legionella regulations closely is essential to control its presence and prevent outbreaks of Legionnaires’ disease, of which there are about 500 cases every year in the UK. See our case studies for significant outbreaks.

How much does it cost to test for Legionella?

The cost to test for Legionella in water can vary depending on the type of test, the number of samples, and the laboratory performing the analysis. Generally, the cost ranges from £50 to £200 per sample, with basic culture tests being the least expensive and advanced methods like PCR testing being the most costly. Additional costs may include site visits, sample collection, and reporting fees unless this is done in-house!

Is it safe to drink water with Legionella?

Legionella primarily causes infection by inhaling contaminated water droplets, which can occur during activities like showering or within spas.

Ingestion (drinking) poses a lower risk, but vulnerable populations, such as those with weakened immune systems, should avoid exposure. Ensuring water systems are regularly tested and properly maintained helps minimise any potential risks.

Does boiling water kill Legionella?

Yes, boiling water kills Legionella bacteria. Boiling water for at least one minute effectively eliminates Legionella, making the water safe for consumption and other uses. This method is particularly useful for ensuring water safety in domestic settings or during outbreaks.

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