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Glossary
Water standards and regulation

What is Legionella and HSG274 / ACoP L8?

Definition

ACOP L8 is the HSE Approved Code of Practice on controlling legionella bacteria in water systems, and HSG274 is the HSE technical guidance that explains how to meet it.

Who carries the duty

Employers and anyone in control of premises with a water system, including landlords, must assess and control legionella risk. That covers offices, hospitals, care homes, hotels, schools, leisure centers and plants with cooling towers. L8, in its fourth edition from 2013, gives ACOP status to the risk assessment, the appointed responsible person, the written control scheme and its review.

Temperatures and record periods

The HSE's hot and cold water guidance sets these targets.

  • Hot water stored at 60°C or higher
  • Hot water reaching at least 50°C within 1 minute of running an outlet
  • Cold water below 20°C after running sentinel taps for 2 minutes
  • Monitoring and inspection records kept for at least 5 years
  • HSG274 Part 1 on evaporative cooling was reissued as a second edition in March 2024

Continuous temperature and flow on the water twin

Monthly sentinel checks catch a single moment. Where temperature sensors are fitted on hot and cold headers, Aqueduct records them every 60 seconds and alerts when a calorifier return drops below target. Line-level flow shows which branches have gone quiet, which is where little-used outlet flushing should start.

Questions

Legionella and HSG274 / ACoP L8: common questions

ACOP L8 and HSG274 are the HSE's core documents on legionella control in Great Britain. L8 states what a dutyholder must do, and HSG274 explains how in three parts: evaporative cooling systems, hot and cold water systems, and other risk systems. Aqueduct's view is on the legionella compliance page.

ACOP L8 is an Approved Code of Practice with special legal status. Following it is enough to comply on the matters it covers; a dutyholder who does something else must show the alternative is equally effective, which in a prosecution can be harder than following the code.

HSG274 is British guidance with explicit temperature targets. ASHRAE 188 is a US standard that requires a water management program but leaves control limits to the program team. Multinational estates often run both, with site-specific limits written into each program.

No. Sensors add evidence between checks, but the responsible person still owns the risk assessment, control scheme and remedial actions. Continuous temperature and flow data from Aqueduct helps that person focus flushing and inspections where readings drift, and gives auditors a fuller record than monthly checks.

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