Who is the duty holder for Legionella?

The employer or person in control of the premises where work activities are carried on. Landlords with responsibility for water systems in let premises are also duty holders.

How often should sentinel outlets be tested?

Weekly for representative sentinel outlets, monthly for all little-used outlets, and quarterly for calorifier flow and return temperatures — per HSG274 Part 2.

Do I need to sample for Legionella?

Sampling is not always required by law but is expected where control measures may not be effective, after an outbreak, or where risk assessment identifies it — typically at least annually in higher-risk systems.

Water learning hub

Water Hygiene

Legionella risk assessment, monitoring, sampling and remedial works for duty holders under HSG274 and ACOP L8 — with realistic timelines and cost expectations.

In short

The duty holder must identify and assess the risk of exposure to Legionella and implement written control measures under the Approved Code of Practice L8. Reviews are due at least every two years — sooner if the system, use or risk profile changes.

Legal snapshot

What the law says

Health and Safety at Work etc Act 1974: General duty of care to employees and others affected by the undertaking.
COSHH Regulations 2002: Legionella bacteria treated as a substance hazardous to health.
ACOP L8 (4th edition): Legionnaires' disease: the control of legionella bacteria in water systems.
HSG274 Parts 1–3: Technical guidance on evaporative cooling systems, hot and cold water systems, and other risk systems.

On the ground

Common problems & fixes

Legionella risk assessment older than 2 years
Fix, Commission a fresh LRA from a Legionella Control Association (LCA) registered assessor.
Temperature monitoring not recorded
Fix, Weekly sentinel outlet temperatures logged in a written scheme — hot ≥50°C, cold ≤20°C.
TMV strainers not descaled
Fix, Annual TMV service on all high-risk outlets, recorded against the asset register.
Positive Legionella count from sampling
Fix, Follow HSG274 Part 2 remediation: superchlorination or thermal disinfection and resample to clear.

Pillar guide6 min read

Legionella Risk Assessments: HSG274 & ACOP L8 Guide

How to commission, review and act on a Legionella risk assessment under ACOP L8 and HSG274 — control measures, monitoring intervals and remedial routes.

Read the full guide

All water guides

1 guide

Cluster guides for this niche are publishing shortly. The pillar guide above covers the full duty-holder journey while we finish the deeper breakdowns.

FAQ

Frequently asked

Who is the duty holder for Legionella?: The employer or person in control of the premises where work activities are carried on. Landlords with responsibility for water systems in let premises are also duty holders.
How often should sentinel outlets be tested?: Weekly for representative sentinel outlets, monthly for all little-used outlets, and quarterly for calorifier flow and return temperatures — per HSG274 Part 2.
Do I need to sample for Legionella?: Sampling is not always required by law but is expected where control measures may not be effective, after an outbreak, or where risk assessment identifies it — typically at least annually in higher-risk systems.

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