How often should legionella checks and risk assessments be carried out?
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There is no fixed legal interval for the risk assessment: it must be reviewed regularly and whenever it may no longer be valid. HSE's guidance sets the routine checks, including weekly flushing of little-used outlets, monthly temperature checks, quarterly shower head cleaning and annual tank inspections.
What to do, and how often
| Task | How often | Who | Basis |
|---|---|---|---|
| Review the legionella risk assessment | No fixed intervalNo fixed interval: regularly, and after changes to the water system, its use or the building | Dutyholder and appointed responsible person | Guidance HSE's L8 (the Approved Code of Practice and guidance) says to review the assessment regularly and whenever there is reason to suspect it is no longer valid. It sets no fixed period. SourcesS1S2 |
| Flush infrequently used outlets | Every week | Responsible person or nominated staff | Guidance HSG274 Part 2, Table 2.1: weekly, or as indicated by the risk assessment. SourcesS3 |
| Check cold water temperatures at sentinel taps (below 20 degrees C within two minutes) | Every month | Responsible person or water hygiene contractor | Guidance HSG274 Part 2, Table 2.1 lists this check as monthly. SourcesS4 |
| Check hot water temperatures at sentinel points (at least 50 degrees C within one minute, 55 in healthcare) | Every month | Responsible person or water hygiene contractor | Guidance HSG274 Part 2, Table 2.1 lists this check as monthly. SourcesS5 |
| Check calorifier flow and return temperatures (flow at 60 degrees C, return not below 50) | Every month | Responsible person or water hygiene contractor | Guidance HSG274 Part 2, Table 2.1 lists this check as monthly. SourcesS6 |
| Dismantle, clean and descale shower heads, hoses and spray taps | Every 3 months | Responsible person or water hygiene contractor | Guidance HSG274 Part 2, Table 2.1: quarterly, or as indicated by the rate of fouling or other risk factors. SourcesS7 |
| Inspect cold water storage tanks and carry out remedial work | Every year | Water hygiene contractor | Guidance HSG274 Part 2, Table 2.1 lists this inspection as annual. SourcesS8 |
| Inspect and clean calorifiers internally | Every year | Water hygiene contractor | Guidance HSG274 Part 2, Table 2.1: annually, or as indicated by the rate of fouling. SourcesS9 |
| Maintain thermostatic mixing valves, including cleaning strainers and filters | Every year | Competent person | Guidance HSG274 Part 2, Table 2.1: annually or on a frequency defined by the risk assessment. SourcesS10 |
| Weekly dip slide test of cooling system water Applies to: Buildings with cooling towers or evaporative condensers | Every week | Water treatment provider or trained staff | Guidance HSG274 Part 1 says cooling system water should be tested weekly using dip slides or similar. SourcesS12 |
| Legionella sampling of cooling system water Applies to: Buildings with cooling towers or evaporative condensers | Every 3 months | Water treatment provider | Guidance HSG274 Part 1 says routine monitoring for legionella should be undertaken at least quarterly. SourcesS11 |
Where a row says who or what it applies to, the task is for that case only.
The law
The Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 require employers and those in control of premises, including landlords, to assess and control the risk from legionella. HSE's Approved Code of Practice L8 explains how: identify and assess sources of risk, prepare a written scheme, implement and monitor it, keep records and appoint a responsible person. The law sets no test frequencies.
The standard
HSE Approved Code of Practice L8 (fourth edition, 2013) and technical guidance HSG274 Parts 1 to 3. HSG274 was reissued in 2024, with changes to Part 1 (cooling systems) only.
Records to keep
- Current legionella risk assessment with review dates
- Written scheme of control
- Temperature monitoring and flushing logs
- Tank, calorifier and shower cleaning records
- Laboratory sample results, where sampling is done
- Records kept for at least five years
Notes
The frequencies are HSE guidance, not law, and each one can be varied by the risk assessment: healthcare and care settings usually need tighter controls.
HSG274 says legionella sampling of hot and cold water systems should be carried out where there is doubt about the control regime or where the recommended temperatures are not being consistently achieved. Cooling towers need weekly dip slides and at least quarterly legionella samples.
Who delivers this in the group
Gemini AMPM
Delivered by Gemini AMPM. One number reaches every company in the group, day or night: 0330 043 0080.
Questions people ask
Legionella control in hot and cold water systems: is the interval set in law?
No task on this page has an interval set in legislation. Each one is recommended by guidance. The Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 require employers and those in control of premises, including landlords, to assess and control the risk from legionella. HSE's Approved Code of Practice L8 explains how: identify and assess sources of risk, prepare a written scheme, implement and monitor it, keep records and appoint a responsible person. The law sets no test frequencies.
Legionella control in hot and cold water systems: who should carry out each task?
Dutyholder and appointed responsible person: review the legionella risk assessment. Responsible person or nominated staff: flush infrequently used outlets. Responsible person or water hygiene contractor: check cold water temperatures at sentinel taps (below 20 degrees C within two minutes); check hot water temperatures at sentinel points (at least 50 degrees C within one minute, 55 in healthcare); check calorifier flow and return temperatures (flow at 60 degrees C, return not below 50); dismantle, clean and descale shower heads, hoses and spray taps. Water hygiene contractor: inspect cold water storage tanks and carry out remedial work; inspect and clean calorifiers internally. Competent person: maintain thermostatic mixing valves, including cleaning strainers and filters. Water treatment provider or trained staff: weekly dip slide test of cooling system water. Water treatment provider: legionella sampling of cooling system water.
Legionella control in hot and cold water systems: what records should you keep?
Keep these records: current legionella risk assessment with review dates; written scheme of control; temperature monitoring and flushing logs; tank, calorifier and shower cleaning records; laboratory sample results, where sampling is done; records kept for at least five years.
Legionella control in hot and cold water systems: which tasks have no fixed interval?
Review the legionella risk assessment: no fixed interval: regularly, and after changes to the water system, its use or the building.
Sources
Every task and legal statement is supported by at least one source fetched over HTTPS and read on the date shown. Quotes are verbatim and 25 words or fewer. A second, independent verification pass re-fetched every source and re-read the legislation on 5 October 2026. Intervals taken from British Standards were checked against published summaries of those standards by trade bodies and government guidance, because the standards themselves are paid publications.
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Health and Safety Executive · Fourth edition, 2013 · read on
“Arrange to review the assessment regularly and specifically whenever there is reason to suspect it is no longer valid.”
Supports: Review of the risk assessment: regularly and when no longer valid
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Health and Safety Executive · Fourth edition, 2013 · read on
“To comply with their legal duties, dutyholders should”
Supports: What dutyholders must do to comply
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Weekly, or as indicated by the risk assessment”
Supports: Weekly flushing of infrequently used outlets (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Check temperatures at sentinel taps (typically those nearest to and furthest from the cold tank”
Supports: Monthly cold water temperature check at sentinel taps (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“take temperatures at sentinel points (nearest outlet, furthest outlet and long branches to outlets)”
Supports: Monthly hot water temperature check at sentinel points (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Check calorifier return temperatures (not below 50 °C)”
Supports: Monthly calorifier flow and return temperature check (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Quarterly or as indicated by the rate of fouling or other risk factors”
Supports: Quarterly cleaning and descaling of showers and spray taps (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Inspect cold water storage tanks and carry out remedial work where necessary”
Supports: Annual inspection of cold water storage tanks (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Annually, or as indicated by the rate of fouling”
Supports: Annual internal inspection and cleaning of calorifiers (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 2: hot and cold water systems ↗
Health and Safety Executive · First published 2014; reissued 2024 (the 2024 second edition updated Part 1 only) · read on
“Annually or on a frequency defined by the risk assessment”
Supports: Annual maintenance of thermostatic mixing valves (Table 2.1)
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Legionnaires' disease: Technical guidance HSG274 Part 1: evaporative cooling systems ↗
Health and Safety Executive · Second edition, 2024 · read on
“Routine monitoring, specifically for the presence of legionella, should be undertaken at least quarterly.”
Supports: Cooling towers: legionella sampling at least quarterly
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Legionnaires' disease: Technical guidance HSG274 Part 1: evaporative cooling systems ↗
Health and Safety Executive · Second edition, 2024 · read on
“Cooling system water should be tested weekly, using dip slides (or similar).”
Supports: Cooling towers: weekly dip slides