Temperature control is the primary way legionella risk is managed in a hot and cold water system: keep hot water hot, keep cold water cold, and legionella cannot multiply. This tool checks your readings against the thresholds in HSG274. It tells you which readings are in range and what a reading out of range means. It does not confirm that your system is safe, and a single set of temperatures is one data point, not a risk assessment. For the full picture see legionella temperature control.
Your temperature check
Thresholds are from HSG274. Healthcare premises under HTM 04-01 require hot water to reach 55°C at the outlet. A reading in range shows control at that outlet at that moment; it is not proof the whole system is safe. Record every reading in your log book.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
The thresholds this tool uses
| Reading | In range | Why |
|---|---|---|
| Hot water at the outlet | 50°C or above within 1 minute (55°C healthcare) | Above 50°C legionella cannot multiply and begins to die. |
| Stored hot water | 60°C or above | At 60°C legionella is killed within a few minutes. |
| Cold water at the outlet | Below 20°C within 2 minutes | Below 20°C legionella stays dormant. |
The danger zone between these is roughly 20°C to 45°C, where legionella multiplies fastest. A reading that lands in that band is the warning sign. For what each reading means and how the control regime fits together, see legionella temperature control and the temperature chart.