If you have recently been told you need a Legionella risk assessment, you are not alone. Many
landlords, business owners and managing agents first hear about it when purchasing a property,
taking on a new tenancy, responding to insurer requests, or reviewing compliance obligations. This
guide explains in simple terms what a Legionella risk assessment is, why you may need one, and
what it involves.

What Is Legionella?

Legionella is a bacteria that can grow in water systems if conditions allow it to multiply. It becomes
a risk when water is stored or recirculated, temperatures sit between 20°C and 45°C, water
stagnates, or aerosols are created (for example from showers or taps). The illness associated with
Legionella is Legionnaires’ disease, a form of pneumonia.

Do I Legally Need a Risk Assessment?

In the UK, if you are an employer, landlord, managing agent, or the person responsible for a
building’s water systems, you are legally required to assess and control the risk of Legionella. In
smaller properties this person is often the same individual who owns or manages the building.

What Is a Legionella Risk Assessment?

A Legionella risk assessment is a structured review of your water systems to determine:

• Where Legionella could grow
• Who could be exposed
• Whether current controls are adequate
• What actions (if any) are required
  It is not simply taking a water sample. The assessment focuses on system design, operation and
  control measures.

What Does an Assessor Do?

A proportionate assessment may include identifying incoming water supplies, reviewing hot and
cold water systems, checking storage tanks or water heaters, temperature testing representative
outlets, looking for stagnation risks, and reviewing maintenance records and management
procedures.

What Happens After the Assessment?

You should receive a written report that clearly describes your system, identifies risks (if present),
recommends proportionate control measures, and outlines monitoring requirements. The report
should be practical and site-specific.

Key Takeaway

A Legionella risk assessment is not about creating paperwork. It demonstrates that you understand
your water system, have considered risks, and have appropriate controls in place. For many small
properties, the risk level is low — but it still needs to be properly assessed and documented.