Legionella Risk Assessment: Landlord Guide (2026)

Key Takeaways

• All landlords have a legal duty to assess and manage Legionella risk under HSE Approved Code of Practice L8
• There is no such thing as a legally required "Legionella certificate" — companies selling these are overcharging for something the law doesn't require
• For standard domestic properties with combi boilers, you can conduct the assessment yourself for free using the checklist in this guide
• Professional assessments cost £75–£150 and are recommended for complex systems (water tanks, multiple properties, HMOs)
• Legionella bacteria thrive between 20°C and 45°C — keep hot water above 60°C and cold water below 20°C to eliminate risk
• You must inform tenants about basic water safety responsibilities, including flushing the system if they're away for more than a week

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One of the most common myths in the buy-to-let world is that "Legionella certificates" are mandatory — like Gas Safety records or EICRs. They aren't.

However, the risk assessment is legally required. If a tenant contracts Legionnaires' disease from your property, you could face prosecution under the Health and Safety at Work Act — with penalties including unlimited fines and up to 2 years imprisonment.

The confusion between "assessment" (required) and "certificate" (not required) has created a cottage industry of companies selling overpriced services to worried landlords. This guide clears up what you legally must do, what is a waste of money, and how to protect your tenants without overspending.

This guide is part of our complete Landlord Compliance resource.

What is Legionella?

Legionella is a genus of bacteria that can cause Legionnaires' disease — a severe form of pneumonia that kills approximately 10–15% of otherwise healthy people who contract it (higher in the elderly or immunocompromised). The bacteria are found naturally in water sources and become dangerous when they multiply in man-made water systems.

How People Get Infected

Legionella is transmitted by inhaling water droplets (aerosol) containing the bacteria — not by drinking contaminated water. The primary risk sources in domestic properties are:

• Shower heads — produce the fine mist that carries bacteria into the lungs
• Taps — splashing creates smaller aerosol droplets
• Hot tubs and whirlpool baths — very high risk due to extensive aeration

The Temperature Sweet Spot

Legionella bacteria multiply most rapidly between 20°C and 45°C. Below 20°C, they become dormant (but don't die). Above 60°C, they're killed within minutes.

This is why the fundamental control measure is simple: keep hot water hot and cold water cold.

The Legal Requirement

Under the Health and Safety Executive (HSE) Approved Code of Practice L8 and the associated technical guidance document HSG274 Part 2 (hot and cold water systems), landlords must:

1. Identify and assess the sources of Legionella risk in their property
2. Manage any risks identified
3. Prevent or control any risks that cannot be eliminated
4. Keep records of the assessment and any actions taken
5. Review the assessment regularly — at least every 2 years, or whenever changes are made to the water system

What "Reasonably Practicable" Means

The HSE explicitly recognises that domestic hot and cold water systems in most residential properties represent low risk, provided basic controls are in place. The assessment does not need to be carried out by a specialist — a competent landlord can do it themselves.

The "Certificate" Myth

There is no such thing as a legally mandated "Legionella Test Certificate" for domestic rental properties. The HSE does not require water testing for standard domestic systems.

Many letting agents and property management companies tell landlords they need a "Legionella certificate" costing £100–£200+. While a professional risk assessment is a valid service (typically £75–£150), the idea that you need a formal certificate similar to a Gas Safety Record or EICR is incorrect.

What the HSE actually says: "For most domestic hot and cold water systems in residential properties, a risk assessment will be straightforward. You may be able to carry it out yourself." — HSE Legionella guidance

DIY vs Professional Assessment

When to Do It Yourself (Free)

A self-assessment is appropriate if:

• The property has a combi boiler (no stored hot water — lowest risk)
• The property is a standard domestic dwelling (not an HMO with complex plumbing)
• The water system has no cooling towers, spa baths, or water storage tanks
• You are a competent landlord who can follow a structured checklist

When to Hire a Professional (£75–£150)

A professional assessment is recommended if:

• The property has a hot water storage cylinder or cold water storage tank (typically found in older properties with vented systems)
• The property is an HMO with multiple bathrooms and longer pipe runs
• The property has spa baths, whirlpool baths, or water features
• The property has been vacant for extended periods (more than a month)
• You manage multiple properties and want systematic documentation

Beware of Overpricing

If a company is charging £200+ for a simple domestic risk assessment, or insisting you need regular water testing for a standard property with a combi boiler, get a second opinion.

The DIY Risk Assessment Checklist

If you're conducting the assessment yourself, work through this checklist annually (or between tenancies) and keep a signed, dated copy with your other compliance records.

1. Identify the Water System Type

2. Check Water Temperatures

Use a simple digital thermometer (£5–£10 from any hardware shop):

• Hot water at the cylinder or boiler: Should be stored at 60°C or above (check the boiler/cylinder thermostat)
• Hot water at the tap: Should reach 50°C within one minute of running. If it takes longer, the pipe run is too long or the temperature is set too low.
• Cold water at the tap: Should be below 20°C within 2 minutes of running. If it's warmer, check whether cold pipes run alongside hot pipes (poor insulation) or through warm spaces (boiler cupboard, airing cupboard).

3. Identify Stagnation Points

Stagnant water is where Legionella multiplies. Check for:

• Rarely used outlets: Guest room showers, utility room taps, en-suite bathrooms that aren't used regularly
• Dead legs: Sections of pipe that are capped off but still connected to the live system (common after bathroom relocations or kitchen refits)
• External taps: Garden taps that are rarely used, especially in winter

Action: Flush unused outlets weekly (run each tap and shower for 2 minutes). If dead legs exist, have a plumber remove or cap them properly.

4. Inspect Shower Heads and Hoses

Shower heads and flexible hoses are the highest-risk components because:

• They produce the finest aerosol (mist) — the particle size that reaches the lungs
• Scale, limescale, and biofilm build up inside them, creating an environment for bacterial growth
• They're rarely cleaned between tenancies

Action: Dismantle, clean, and descale all shower heads and hoses at every tenancy changeover. Use a dedicated descaling solution or soak in white vinegar for 2–4 hours.

5. Inspect Water Storage Tanks (If Present)

If the property has a cold water storage tank (usually in the loft):

• Tank has a tight-fitting, intact lid (no gaps for insects, debris, or animals to enter)
• Tank is properly insulated (prevents temperature rising above 20°C in summer)
• Water is clear (no discolouration, sludge, or sediment at the bottom)
• No dead animals, insects, or debris in or around the tank
• Overflow pipe is intact and screened (to prevent insects/birds entering)

If the tank fails any of these checks, arrange immediate remediation before a new tenancy begins.

Tenant Communication

You must inform tenants about their responsibilities in maintaining water safety. This isn't about scaring them — it's about practical cooperation:

What to Include in Your Tenant Welcome Pack

1. Do not lower the hot water temperature below 60°C on the boiler/cylinder thermostat (explain why)
2. Report problems promptly — if hot water isn't hot, or if there's unusual discolouration or smell
3. If you go away for more than a week, run all taps and showers for 2 minutes upon return before normal use
4. Don't block air gaps on taps (the small space between the tap outlet and the basin overflow). These prevent backflow contamination.
5. Clean shower heads regularly — and report any that don't produce a full, even spray pattern

Document that you've provided this information. A simple signed acknowledgment in the tenancy pack is sufficient.

Control Measures Summary

Record Keeping

Keep a dated, signed record of your risk assessment alongside your other compliance documentation:

• Gas Safety Certificate (annual, mandatory)
• EICR (5-yearly, mandatory)
• EPC (10-yearly, mandatory)
• Legionella Risk Assessment (reviewed every 2 years or between tenancies)

Store digital copies in cloud storage for easy retrieval if requested by a local authority.

Conclusion

Don't be bullied into paying for "certificates" you don't need — but don't ignore the risk either. A simple written assessment, reviewed biennially or between tenancies, is usually enough to comply with the law and protect your tenants.

The key controls are straightforward: keep hot water hot (60°C+), cold water cold (below 20°C), flush unused outlets, and clean shower heads. Document everything.