Legionella FAQs & Compliance Guidance (UK)

Legionnaires’ disease is a severe form of pneumonia caused by inhaling tiny water droplets contaminated with Legionella bacteria. It typically spreads through man-made water systems like cooling towers, hot and cold water tanks, showers, and air conditioning units. The disease can be life-threatening, especially for vulnerable individuals, making risk assessment and control essential for workplaces, landlords, and healthcare environments.

Legionella bacteria are naturally present in freshwater sources like rivers, lakes, and ponds. However, the greatest risk arises when they contaminate man-made water systems – such as cooling towers, hot and cold water services, showers, and storage tanks – where conditions allow them to multiply. The bacteria thrive in temperatures between 20°C and 45°C, especially when systems contain nutrients like rust, sludge, scale, or biofilm.

While anyone can contract Legionnaires’ disease, certain groups are at higher risk. These include people over 45 years of age, smokers, heavy drinkers, and individuals with chronic respiratory conditions, kidney disease, or a weakened immune system. The disease poses a greater threat in workplaces, care homes, and healthcare settings, where vulnerable individuals may be exposed to contaminated water systems.

Legionella bacteria cannot be seen with the naked eye, making it difficult to detect without testing. However, risk factors such as stagnant water, poor temperature control, scale, and biofilm build-up can indicate an increased likelihood of contamination. Regular monitoring and testing are essential.

Legionella bacteria thrive in water temperatures between 20°C and 45°C. To control the risk, hot water should be stored at 60°C or above and distributed at a minimum of 50°C. Cold water should be kept below 20°C. Maintaining these temperatures helps prevent bacterial growth within water systems.

Responsibility for Legionella control falls to the duty holder, typically the employer, building owner, or person in control of the premises. This individual must ensure that risks are assessed, control measures are in place, and ongoing monitoring is carried out in line with HSE guidance.

Yes, landlords in the UK have a legal duty to assess and control the risk of Legionella in rental properties. This applies to all types of residential accommodation. While not every property requires complex testing, a documented risk assessment is essential to demonstrate compliance with health and safety regulations.

The law clearly states if you are a Landlord and rent out your property then you have a duty under Health and Safety Law to consider the risk posed by Legionella bacteria. The ACoP L8 (3rd edition) also states Landlords must assess the risk from exposure to legionella to their tennants.

In most cases the risk assessment is simple and straight forward, however for more complex systems or if the Landlord is not able / competent to carry out the assessment they can use a specialist Water Treatment Company like Dantek, to carry out the legionella risk assessments and advise on any actions required.

Do make contact if you are a Landlord and are unsure about what to do about Legionella control or if you would just like some further advice about the prevention and contol of legionnaires disease.

https://www.hse.gov.uk/legionnaires/legionella-landlords-responsibilities.htm

To comply with the Health and Safety Executive (HSE) guidance – including ACoP L8 and HSG274 – you must first carry out a Legionella risk assessment. This identifies potential risks within your water systems that could affect staff, residents, or the public. Based on the findings, you must implement appropriate control measures to prevent or reduce the risk of Legionella growth, such as maintaining water temperatures, cleaning tanks, and monitoring systems regularly.

A Legionella risk assessment should be reviewed regularly and whenever there are changes to the water system, building use, or occupancy levels. In general, reviews are recommended at least every two years, but more frequent reviews may be required depending on risk level. Keeping assessments up to date ensures ongoing compliance with HSE guidelines.

This depends on the risk assessment and control methods being used. In some circumstances it will be required, however it needs to be done at a UKAS accredited laboratory and will require specialist help. Dantek can provide advice on sample frequency and locations, and what to do if Legionella is detected.

Legionella testing involves collecting water samples from key points within a system, such as tanks, outlets, and pipework. These samples are then analysed in a UKAS-accredited laboratory to detect the presence and concentration of Legionella bacteria. Results help determine if corrective actions are required.

Temperature is usually used in hot and cold water systems, by keeping hot water at above 60 degrees and ensuring it is above 50 degrees at the outlets. Cold water should be kept at below 20 degrees.

There are other methods which can be used if temperature is not an option, such as copper/silver ionisation and chlorine dioxide.

Cooling towers / systems are often treated with biocides. There are other treatment strategies available such as ultra violet (UV) irradiation.

Often a site visit by one of our sales team is the best way to establish exactly how much a risk assessment will cost. However; we are often able to provide a guide price if you know roughly the size and type of building. For example how many floors, what it is used for, whether there are any cold water storage tanks, number of calorifiers and if there are any cooling towers. One of our sales team would be happy to talk through on the phone any requirements and enquiries.

Dantek StaySafe subscription is an optional add-on service for customers who have purchased a Legionella Risk Assessment within the last 6 months. It provides continuous compliance and peace of mind by including:

• Unlimited updates to your risk assessment throughout the year, including revised schematics.

• An annual compliance audit and review, with a site visit if required.

• Unlimited access to our expert technical helpline for advice and guidance.

• A positive results resolution guarantee, with a dedicated case manager if Legionella is detected.

StaySafe helps you save time, reduce risk, and remain fully compliant with HSG274 and BS8580 — without the hassle of arranging ad-hoc updates or external consultants.

👉 To find out more or to enrol, email us at [email protected]

Failure to manage Legionella risks can result in serious legal consequences, including fines, prosecution, and reputational damage. The Health and Safety Executive (HSE) can take enforcement action if duty holders fail to meet their obligations. In severe cases, non-compliance can lead to imprisonment.

• Call Dantek for expert advice and support.
• Order a copy of the Approved Code of Practice and guidance Legionnaires’ Disease: The control of legionella bacteria in water systems L8.
• Contact the Water Management Society (WMS): www.wmsoc.org.uk