Do I need a legionella risk assessment for a small office?

Yes. If your office has employees and a water supply, you need a legionella risk assessment, because you are an employer under the Health and Safety at Work etc. Act 1974 and the water system in your premises is a workplace hazard you are expected to have assessed. There is no exemption for being small. What being small changes is the size of the answer: a two-room office with a mains-fed cold supply and an under-sink water heater is a thirty-minute assessment with a thermometer, not a consultancy engagement.

Why there is no small-business exemption

The legionella duty flows from general health and safety law, not from a legionella-specific statute, and general health and safety law does not switch off below a certain size. ACOP L8 applies wherever there is a reasonably foreseeable risk of exposure to legionella from a water system at work, and an office kitchenette and loo qualify. People sometimes cite a five-employee threshold; that figure relates to written records under the general risk assessment rules, and L8 expects legionella findings and controls to be recorded regardless, because an unrecorded assessment is one you cannot evidence. The practical rule is simple: always write it down, whatever your headcount.

What the assessment actually involves in a small office

Forget the word "assessment" and picture the walk. In a typical small office it looks like this:

1. Find where hot water comes from. An instantaneous heater or a small point-of-use unit means no stored hot water and the simplest possible picture. A cylinder means stored water, so check it is held at 60°C.
2. Take temperatures at the far outlets. Run the hot tap furthest from the source and confirm it reaches at least 50°C within a minute; run cold taps and confirm they drop below 20°C within two minutes. The temperature checker records the readings against the right limits.
3. List the little-used outlets. The loo nobody uses since the team shrank, the kitchenette in the meeting room, the shower installed for cyclists that three people use. Anything drawn less than about weekly goes on a weekly flush, recorded, per our guide to flushing little-used outlets.
4. Look for dead legs. Capped pipe stubs from a removed dishwasher, a water heater, or a former tenant's fit-out. See what are dead legs and either remove them back to the live run or flush them.
5. Check any cold water tank. If the office has one, it should be lidded, insulated, and clean. Many small offices are fully mains-fed and have none, which closes the question.
6. Note who is exposed and set the controls. Staff and visitors, plus anyone vulnerable. Controls are usually just the temperature regime, the flushing schedule, and cleaning any shower head quarterly.
7. Write it down and name the person. Record what you found, the controls, who checks them, and when you will review. That document is the assessment.

Can you do it yourself?

For the system described above, yes. Competence is what the law asks for, and for a simple office it means being able to trace the pipework, take a temperature, recognise a dead leg, and set a flushing schedule. The HSE expects simple, low-risk premises to be assessed in-house. Bring in outside help when the office stops being simple: shared tanks and risers in a multi-let block, a cooling tower or evaporative condenser on the roof, process water, or a healthcare or care use on the premises. Our pages on doing your own assessment and whether you need one go deeper on both points.

If you rent the office

In a multi-let building the duty is usually split, and the split is worth pinning down. The landlord or managing agent typically assesses and controls the landlord's system, the shared tanks, risers, and plant, while you assess the part inside your demise: your water heater, your outlets, your dead legs from the previous tenant's kitchen. Ask the agent what their assessment covers, get the boundary in writing, and make sure neither of you is assuming the other has the middle of the system. A gap between two half-assessments is a classic finding after the fact.

Keeping it alive

An assessment in a drawer does nothing. The controls it names, the weekly flush of the unused loo, the monthly temperature at the far tap, the quarterly shower-head clean, need doing and recording, and a log book keeps them in one place. Review the assessment when the office changes: a refit, a new water heater, a change in occupancy, or a long closure. Records should be kept for at least five years. The free risk assessment builder produces the written assessment for a simple office and gives you the structure to keep it current. It records your findings; it does not certify the office, and no document can.