What temperature kills Legionella?
Legionella grows at 20-45C, is held back at 50-60C, and dies faster as temperatures rise. See the kill temperatures and daily control targets.
The UK reference for Legionella control.
Risk assessment, temperature, monitoring and the law, explained for the people who carry the duty.
An independent, free UK Legionella reference. Every figure is cited to HSE, ACoP L8 and the BS standards, and reviewed by an LCA-registered water-safety team.
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Is this water in the danger zone?
Legionella multiplies fastest between 20 and 45°C. Drag the bar or type a reading.
New to the duty? Start here.
- 01What is Legionella? An introduction to the bacteria and disease
Legionella only becomes your problem when warm water sits still and then gets breathed in, understand those two conditions and the whole subject gets simpler.
- 02UK Legionella compliance 101: laws and responsibilities
There is no single Legionella law; the duties come from general health and safety law and land on whoever controls the building, so the real question is who is accountable and what proves control.
- 03Legionella risk assessment basics: what it is and why you need it
A Legionella risk assessment is a decision document, not a certificate; its job is to rank what could grow, who is exposed, and what to fix first.
- 04Temperature control basics for Legionella prevention
Look past single readings and judge whether the whole water system can hold control.
- 05Routine monitoring and flushing: the basics
Flushing and monitoring are the two day-to-day halves of Legionella control; do them as a managed routine, not a tick-box, and you cover most of the everyday risk.
- 06Legionella logbooks: an introduction to record keeping
A logbook's only job is to turn the work you did into proof you can hand to an auditor, an inspector, or whoever inherits the building, and the proof lives in the exceptions, not the green ticks.
Free to read, no sign-up and no paywall. Written for UK duty holders and kept current as guidance changes.
Browse by topic
Ten pillars covering the whole duty, from the science to enforcement.
Basics & science71How the bacterium actually behaves (growth, biofilm, aerosols and the disease), translated into decisions you can make on site.Law & compliance62What the law expects of a duty holder: ACoP L8, HSG274, the standards behind them, and where responsibility really sits.Risk assessment48Doing, reading and acting on a risk assessment that reflects your building rather than a template.Temperature control32The primary control. Keeping hot water hot and cold water cold across a real distribution system, and proving it.Monitoring & sampling47The routine work that generates evidence: temperature checks, flushing low-use outlets, and sampling done properly.Record keeping38Records that survive an inspection: what to capture, how long to keep it, and going paper-to-digital well.Technology29Sensors, remote monitoring, analytics and automation: where they earn their place and where they do not.Building types69Hotels, schools, healthcare, care homes, offices and more. The same duties, very different buildings.Failures & enforcement33How control programmes fail in practice, what enforcement looks like, and the costs of getting it wrong.Best practice51Moving past minimum compliance: water safety plans, culture, audits and where the field is heading.
Tools & calculators
Free, no sign-up. They answer the questions that come up first, and do the small sums that otherwise mean a spreadsheet and a guess.
Do I even need a risk assessment?Answer six questions and find out what UK law expects for your situation.OpenIs this water temperature safe?Type a reading and see where it sits against the control figures, with the source.OpenHow long must I flush this outlet?Work the standing water out of a little-used branch from its length and bore.OpenWhen is my review actually due?Check whether your risk assessment still stands or needs reviewing now.Open
See all 12 toolsGuidance for your building
The duties are the same; the buildings are not.
Most read
The guides people come back to once they are past the basics.
How often should you flush and test for Legionella?
No single flush-and-test schedule fits every building. Here's how to set Legionella flushing, temperature and sampling frequencies from the risk assessment.
Thermostatic mixing valves and Legionella risk
A TMV blends water down to a safe temperature, and into the range Legionella loves. Where to put your checks, what to service, and why valve location matters.
Legionnaires' disease symptoms: early warning signs and when to see a doctor
What Legionnaires' disease feels like in the first days, how it differs from flu or COVID, who is most at risk, and exactly when to ring 111 or your GP.
Flushing little-used outlets: best practices
How to flush little-used taps and showers properly: which outlets to list, how to purge them without spraying aerosol, and how to prove it was done.
Remote water temperature monitoring: benefits and setup
Continuous water temperature data only helps if it changes a decision. How UK teams place sensors, set alerts and prove control without ditching the probe.
Why this matters
The risk, and the liability, are real
Legionnaires’ disease is a serious, sometimes fatal pneumonia, and hundreds of people are diagnosed in England and Wales every year. UK law treats failing to control the risk as a criminal matter, with no upper limit on the fine.
463
confirmed Legionnaires’ cases in England & Wales, 2024
19
deaths in 2023, the latest year published (3.1% case-fatality)
Unlimited
maximum fine for breaching the duty
2 years
maximum prison sentence for those responsible
Sources: UKHSA, legionellosis in residents of England and Wales (2024) and the 2017 to 2023 report (deaths); Health and Safety at Work etc. Act 1974, Schedule 3A. Penalties are the maximum on conviction on indictment; imprisonment applies to individuals responsible.
Enforcement is real
UK prosecutions and fines
These are real prosecutions for failing to control Legionella. Fines now reach six and seven figures, and individual managers, not just the organisation, can be held to account.
£3 million
The £3m fine was reduced to £1.5m on appeal in October 2019.
2018 · a death occurred
Bupa Care Homes (BNH) Ltd
Care home
For more than a year during refurbishment works, Bupa failed to implement the controls and monitoring needed to safely manage a care home’s hot and cold water system, and failed to properly train the staff responsible. The resident is thought to have been infected from a hot tap in his room.
Legionella Control News (2018) ݣ900,000
2024
Sanctuary Housing
Social housing (sheltered)
The landlord poorly managed the Legionella risk in the water system at Vincent Naughton Court, Birkenhead, with staff inadequately trained and supervised. A warning letter told residents the water could be boiled but failed to tell them to stop using their showers.
Inside Housing / HSE (Oct 2024) ݣ600,000
2024 · a death occurred
Amey Community Ltd
Facilities management (prison)
The facilities-management contractor failed to act on a 2016 Legionella risk assessment, had no written scheme of control in place, and did not monitor or maintain safe water temperatures in the prison’s water system.
HSE prosecution report (Dec 2024) ›A selected set of landmark cases; HSE does not publish Legionella prosecutions as a single dataset.
All prosecutions and how courts sentenceFrom the team behind Legionella.io
When you are ready to run it, not just read about it
Legionella.io is published by REMOTE TECH LTD (RT), the UK water-safety technology company behind L8log. L8log brings risk assessment, digital logbooks, remedial tracking and remote temperature monitoring into one compliance ecosystem for duty holders and water-hygiene teams.
Risk Assessment app
Build and update site risk assessments, then track every remedial action through to close-out.
Remote monitoring
Wireless temperature sensors and live dashboards that flag drift before it becomes a failure.
Digital Logbook
Every temperature, flush and sample logged, time-stamped and ready for an inspector.
References & downloads
Things to use and download, not just read.
About this resource
An independent reference you can verify
Legionella.io is a free, independent UK Legionella reference. Every figure is cited to a primary source, so you can check it yourself, and the guidance is reviewed by an LCA-registered water-safety team. It is published by Remote Tech Ltd, who also make L8log, our compliance software: we earn when readers choose L8log, but the guidance never changes to suit it, and where you do not need software we say so.
- Free to read, no paywall, no sign-up
- Every figure cited to HSE, ACoP L8 and the BS standards
- Reviewed by an LCA-registered publisher
- Checked against current UK guidance