24 SEP 2026 5 MIN READ

What is Legionella?

Legionella is a type of bacteria which lives in water. It can grow in different forms of water environments, and under the right conditions can even multiply.

What causes Legionella bacteria to grow?

Legionella bacteria usually grow in certain water environments, such as:

Warm water between 20°C and 45°C

Stagnant water that isn’t flowing properly

Water that’s rich in nutrients

Poorly managed or maintained water systems

Water within biofilms (slimy layers made of bacteria and slime)

In simple terms, this includes things like dirty or poorly maintained water systems, hot tubs, and other water features that aren’t regularly cleaned or kept in good condition.

What is Legionnaires’ disease?

Legionnaires disease is a type of pneumonia caused by Legionella bacteria. This type of disease impacts the lungs. And while uncommon, it can be very serious.

What are the symptoms of Legionnaires’ disease?

The NHS describes the symptoms as including:

A cough
Shortness of breath
Chest pain or discomfort, more so when breathing or coughing
A high temperature
Flu-like symptoms

If you experience symptoms like a persistent cough lasting more than three weeks, coughing up blood, chest pain, or feeling very short of breath, NHS guidance recommends seeking urgent medical advice or a GP appointment immediately.

You can find more information on the NHS website.

How Is Legionnaires’ Disease contracted?

Legionnaires’ disease is caused by breathing in tiny water droplets that contain Legionella bacteria. Inhaling contaminated water can lead to serious lung infections.

Why Is Legionella a concern in rental properties?

Legionella bacteria grow in warm, stagnant water systems. If water isn’t regularly cleaned and maintained, it can become a breeding ground. Common sources include hot water tanks, showers, and other water features. Without proper upkeep, these can pose a serious health risk to tenants.

Do landlords legally need a Legionella risk assessment?

Understanding landlord responsibilities

As a landlord, you are legally responsible for ensuring the health and safety of your tenants. The Control of Substances Hazardous to Health Regulations (COSHH) provides a framework for managing risks related to hazardous substances, including Legionella.

This framework offers guidance on how to identify, assess, and control the risk of Legionella in your property’s water systems, helping you stay compliant and keep your tenants safe.

What does a Legionella risk assessment involve?

A Legionella risk assessment helps to identify potential hazards and outlines steps to control and reduce the risk of Legionnaires’ disease. Failing to carry out this assessment can lead to legal penalties, especially if a tenant becomes ill due to inadequate water system management. Regular testing and maintenance are essential parts of compliant property management.

Identifying potential risk factors

As a starting point, you should inspect all water systems for common issues like:

Stagnant water
Old pipework
Any areas where water may collect without circulation

These are the typical environments where Legionella bacteria can thrive.

Assessing water systems and storage

When inspecting your water systems, ensure they are kept clean, maintain proper temperature control, and look for signs of contamination or wear. Regularly maintaining these systems according to safety standards helps prevent bacterial growth and keeps your water safe.

Do all rental properties need a professional risk assessment?

Low-risk domestic properties

A full professional Legionella assessment may not always be necessary, especially if certain criteria are met:

Simple water systems are in place which don’t include stored water tanks or pipework
The property is properly maintained with regular cleanings
The system is temperature controlled
Low occupancy/limited use of water
No known changes to the water systems
You understand your legal responsibilities under HSE guidelines to ensure compliance with health and safety laws

Not sure if your property qualifies as ‘low-risk’? You can find more detailed information on the Health and Safety Executive website (HSE). Alternatively, you may consider consulting with a water safety professional.

Self-assessment

A Legionella self-assessment may be suitable if your property meets the criteria for being low-risk.

When professional support may be needed

If your property has complex water systems, signs of contamination, or has undergone significant changes, then it’s a good idea to reach out for professional help as they are trained and qualified to perform the assessment accurately and safely. Your safety is a priority and if in doubt, you should always consult a professional.