Legionella Control in Commercial Buildings

Legionella bacteria grow in water between about 20°C and 45°C and spread through fine droplets from taps, showers and cooling systems. Anyone who controls a building with a water system has a duty to assess and manage that risk.

What the law asks for

The HSE's Approved Code of Practice L8 and its technical guidance HSG274 set out what's expected. In short, you need:

• A legionella risk assessment by a competent person
• A written scheme for controlling the risks it identifies
• A named person responsible for running that scheme
• Records of the checks and any remedial work

The risk assessment should be reviewed regularly and whenever something changes, such as new plumbing, a change of use or a long closure.

The routine checks

• Monthly temperature checks at sentinel outlets. Hot water should reach at least 50°C within a minute, and cold water should be below 20°C within two minutes.
• Weekly flushing of outlets that are rarely used, so water doesn't stagnate.
• Calorifier checks, with stored hot water kept at 60°C or above.
• Showerhead cleaning and descaling, usually every quarter.
• TMV servicing, so thermostatic mixing valves stay safe and clean.

Where buildings slip up

The most common problems are dead legs left after refits, outlets nobody flushes, and records that stop when a staff member leaves. A planned maintenance contract keeps the checks going and keeps the evidence in one place.