Do I need to do Legionella Sampling? Everything You Need to Know About Legionella Risk Assessments.

Legionella sampling and Legionella risk assessments are two critical elements in maintaining a safe water system, especially in commercial, industrial, and healthcare environments. Whether you’re a facilities manager, landlord, business owner, or duty holder, understanding when Legionella sampling is required and how to conduct a Legionella risk assessment can help you stay compliant, protect users, and avoid costly outbreaks.

What Is Legionella and Why Does It Matter?

Legionella is a type of bacteria found in natural and man-made water systems. When conditions are right, such as warm temperatures (20–45°C), stagnant water, and poor system maintenance. Legionella can multiply and become airborne in small droplets, potentially causing Legionnaires’ disease.

This serious lung infection can be fatal, especially for older adults and people with weakened immune systems. That’s why regular monitoring through Legionella sampling and risk assessment is vital.

What Is Legionella Sampling?

Legionella sampling is the process of collecting and testing water samples from a building’s water system to check for the presence and levels of Legionella bacteria. Sampling can identify potential issues early and verify whether control measures—like temperature regulation and disinfection—are working effectively.

It’s an essential part of managing water safety in high-risk environments such as:

• Hospitals and care homes

• Hotels and leisure center's

• Office buildings and factories

• Educational institution

  
  

BS 7592:2022 is a British Standard published in 2022. It sets out procedures to test water systems for the presence of legionella bacteria.

A key aspect of the revised BS 7592 standard is the requirement for a clear and justifiable reason to conduct water sampling for Legionella bacteria. Routine sampling is not necessary if the water system is operating effectively, remains under control, and shows no indication of elevated contamination levels.

However, there are valid scenarios where Legionella sampling becomes essential, including:

• A failure in the control measures designed to ensure the safety of the water system.

• The introduction of individuals who are more vulnerable to Legionnaires’ disease and who were not previously using the system.

What Is a Legionella Risk Assessment?

A Legionella risk assessment is a legal requirement in many countries (including the UK) and involves a detailed evaluation of a building’s water systems to determine the potential for Legionella growth and transmission.

An effective Legionella risk assessment includes:

• Identifying potential sources of risk (e.g., cooling towers, hot water systems)

• Evaluating current control measures

• Recommending actions to reduce or eliminate risk

• Reviewing records, maintenance schedules, and system schematics

  

  Water testing Identifies early signs of contamination or system failure.

  
  

When Is Legionella Sampling Required?

According to guidelines such as HSE’s HSG274 in the UK, Legionella sampling is not always required by default, but it becomes necessary under certain circumstances:

You need Legionella sampling if:

• Your Legionella risk assessment identifies high-risk areas.

• The system includes cooling towers, spa pools, or complex hot and cold-water systems.

• Control measures are not performing effectively or haven’t been verified.

• The property serves vulnerable populations (e.g., hospitals, care homes).

• There has been a suspected case or outbreak of Legionnaires’ disease.

• You are commissioning or recommissioning a water system after shutdown.

  
  

Even though not legally required, routine Legionella sampling can give peace of mind and protect your business reputation.

How long does Legionella sampling take?

The time it takes to perform Legionella sampling depends on the size and complexity of the water system, but here’s a general breakdown:

On-site sampling:

• Small systems (e.g., single outlets or small buildings): Sampling can take 30 minutes to 1 hour.

• Larger or complex systems (e.g., hospitals, industrial sites): It can take several hours to a full day to collect all necessary samples.

  
  

Sampling involves:

• Identifying representative outlets (taps, showers, tanks, etc.)

• Taking hot and cold water samples

• Measuring temperature and sometimes disinfectant levels (e.g., chlorine)

  
  

Laboratory analysis: Legionella sampling in 14 days.

• Once samples are collected and sent to a UKAS-accredited lab: Standard culture method: Results in are usually provided in 14 days.

  
  

Do Landlords and Employers Need Legionella Risk Assessments?

Yes. If you are a landlord, employer, or duty holder, you are legally responsible for the health and safety of those who use your premises. This includes taking steps to prevent Legionella exposure through regular Legionella risk assessments and, where necessary, Legionella sampling.

Failing to carry out a Legionella risk assessment can lead to fines, legal action, and serious health consequences for occupants.

 What are the Benefits of Legionella Sampling?

Even when not mandatory, Legionella sampling provides several advantages:

• Early detection of bacteria in the system

• Validation of control measures and treatment systems

• Regulatory compliance for high-risk premises

• Reputation management and reduced liability

• Better insight into system performance over time

  
  

How to Carry Out Legionella Sampling

Legionella sampling should be performed by trained professionals using UKAS-accredited labs (or equivalent in your region). A typical process includes:

1. Identifying sampling points – such as taps, outlets, storage tanks, and showers

2. Collecting samples using sterile techniques

3. Transporting to a certified lab under controlled conditions

4. Analysing results and comparing them to acceptable thresholds

5. Taking action if Legionella levels exceed safe limits

What to do If Legionella Is Found.

If Legionella bacteria is detected during sampling, immediate actions must be taken, including:

• Disinfection of the water system (e.g., thermal or chemical treatment)

• Reviewing and updating the Legionella risk assessment

• Investigating potential causes like dead legs or poor temperature control

• Re-sampling after remedial actions to ensure effectiveness

  
  

Do You Need Legionella Sampling?

If your Legionella risk assessment highlights high-risk conditions, or if your property serves vulnerable groups, then yes, Legionella sampling is recommended and sometimes required.

Even if not legally mandated, regular sampling and monitoring are best practices for maintaining water safety and legal compliance.

Key Takeaways

• Legionella sampling helps detect and control Legionella bacteria in water systems.

• A Legionella risk assessment is legally required and forms the basis for determining if sampling is necessary.

• You should conduct sampling in high-risk buildings, healthcare facilities, or if control measures are questionable.

• Failing to assess and manage Legionella risks can lead to serious legal and health consequences.

  
  

Need Help with Legionella Sampling or a Legionella Risk Assessment?

Whether you manage a single property or a portfolio of facilities, our expert consultants are City and Guilds qualified and can help you stay compliant, protect your occupants, and avoid unnecessary risks.

Contact us today for professional Legionella risk assessments and Legionella sampling services.

About the Author:

Craig Taylor is the owner of Absolute Water Compliance and an experienced water hygiene professional with 20 years’ experience working in legionella prevention and ACoP l8 related work.