Legionella Risk Assessment Guide

For UK homeowners, a Legionella risk assessment ensures your water system is safe, efficient, and free from conditions that encourage bacterial growth. For landlords, this assessment is not just a safety recommendation but a legal requirement under UK health and safety legislation to ensure the protection of tenants.

What Does the Work Involve?

• System Mapping: A visual inspection of the entire water system, including cold water storage tanks, cylinders, and all outlets (taps and showers).
• Temperature Testing: Measuring water temperatures at the boiler, the return, and various outlets to ensure they fall outside the "danger zone" (20°C to 45°C).
• Aerosol Risk Identification: Identifying components that create fine mists, such as power showers or spray taps, which are the primary route for Legionella inhalation.
• Stagnation Check: Finding "dead legs" (redundant pipework) or infrequently used outlets where water can sit and breed bacteria.
• Asset Condition Survey: Checking that cold water tanks are properly lidded, insulated, and free from debris, rust, or organic growth.
• Reporting: Providing a written document detailing findings, risk levels, and a schedule for necessary remedial actions.

Typical Costs

The cost of a Legionella risk assessment in the UK depends primarily on the size of the property and the complexity of the plumbing system. Prices usually include the site visit, the physical testing, and the digital or physical report.

Factors affecting the price include your location (London and the South East typically command higher rates) and whether you require additional services like showerhead descaling or water tank disinfection as part of the visit.

How Long Does It Take?

• Small Flat: 30–45 minutes. These properties often have direct mains-fed systems which are quicker to inspect.
• Standard Family Home: 1–1.5 hours. This allows time to locate and inspect the loft tank and check multiple bathrooms.
• Large Property or HMO: 2–3 hours. More time is needed for complex systems with secondary return pumps or multiple storage vessels.
• Report Turnaround: Usually 24–48 hours after the site visit.

DIY or Professional?

While a DIY assessment is technically possible for a private homeowner, it is rarely recommended. Professionals use calibrated thermometers and have the expertise to spot "hidden" risks like pipework dead legs behind walls. For landlords, the law requires a "competent person" to carry out the assessment. If you lack the technical knowledge of plumbing systems, you may fail to meet your legal duty of care, leaving you liable in the event of an outbreak.

Choosing the Right Tradesperson

• Accreditations: Look for assessors registered with the Legionella Control Association (LCA) or those with City & Guilds qualifications in Legionella management.
• Insurance: Ensure they hold Professional Indemnity insurance specifically covering Legionella-related work.
• Independence: Ideally, use an assessor who provides the report independently of any remedial plumbing work to ensure an unbiased view.
• Questions to Ask:
  • Do you use calibrated digital thermometers for all temperature checks?
  • Will the report include a schematic diagram of my water system?
  • Are you familiar with the specific requirements for HMOs (if applicable)?

UK Regulations

Legionella management is governed by strict UK standards. Compliance ensures both safety and legal protection for property owners.

• ACoP L8: The primary Approved Code of Practice for the control of Legionella bacteria in water systems.
• HSG274: Technical guidance that provides practical advice on how to comply with L8.
• Health and Safety at Work Act 1974: The overarching legislation that requires landlords to protect tenants from health risks.
• Paperwork: You should receive a written Risk Assessment (valid for 2 years or until the system changes) and a logbook if ongoing monitoring is required.

Common Problems

• Dead Legs: Pipes leading to removed radiators or capped-off sinks where water stagnates. These must be cut back as close to the main line as possible.
• Low Water Heater Temperatures: Setting your boiler too low to save energy can allow bacteria to multiply. Hot water should be stored at 60°C.
• Uncovered Water Tanks: Loft tanks without lids allow dust, insects, and birds to enter, providing "food" for bacteria.
• Scaling: Limescale on showerheads and taps provides a protective home for Legionella; regular descaling is essential.

Frequently Asked Questions

Is a Legionella test the same as a Risk Assessment?

No. A risk assessment is a physical inspection of the system's design and temperature. A "test" usually refers to water sampling (lab analysis), which is generally only required if the assessment identifies a high-risk scenario or an outbreak is suspected.

How often do I need a Legionella Risk Assessment?

There is no fixed legal timeframe, but the industry standard is every 2 years. However, you must review the assessment if there are changes to the water system, the building's use, or if new guidance is published.

Do I need an assessment for a mains-fed combi boiler system?

Yes, though the risk is lower. While these systems lack a large storage tank (a primary risk site), they still have showerheads and pipework where stagnation or incorrect temperatures can occur.

Can a landlord do their own Legionella assessment?

The law states the assessor must be "competent." If a landlord understands the water system, can measure temperatures accurately, and knows the risks, they can do it. However, most prefer a professional to ensure the report is legally robust.

What happens if Legionella is found in my home?

If a risk is identified, the system usually requires a chemical disinfection (chlorination) or a thermal shock (flushing with very high-temperature water). Physical defects, like dead legs, should be removed by a plumber.