An office feels like the safe end of the Legionella spectrum. No patients, no spa pool, usually no cooling tower on the roof — just taps, toilets and a kitchen sink. That comfort is exactly where offices come unstuck.
The risk in an office is quiet, not dramatic. It hides in the floor that has been half-empty since the firm went hybrid, the cyclists’ shower at the back of the building, the run of pipe that was capped off in the last fit-out and never pulled out. Warm water sits still in those places, and Legionella does its best growing in water that is stagnant and lukewarm rather than properly hot or properly cold [1].
So office water safety has far less to do with heavy plant than with two unglamorous things: under-use, and who actually owns which pipe. The mistakes below are the ones that swallow offices that were sure they were low-risk.
The mistakes that catch offices out
”It’s just an office, so it must be low-risk”
What it looks like: a thin risk assessment from years ago, one annual sample, and a sense that the box is ticked because nothing here looks dangerous.
Why it happens: offices lack the obvious villains. No showers in every room, no vulnerable occupants, no obvious aerosol. The trouble is that risk follows the use pattern, not the building type. Hybrid working quietly turned a lot of busy floors into intermittently-used ones, and intermittently-used outlets are the classic place for warm, still water to build up [1]. Judge the building by how its water actually moves now, not by how a full office used to behave.
The fix: re-walk the system against current occupancy and ask which outlets are genuinely used every day. The ones that are not are your real list.
The shower nobody will admit to owning
What it looks like: an end-of-trip or cyclists’ shower, a small gym, or an accessible washroom that gets used a handful of times a week and otherwise sits idle.
Why it happens: people don’t think of these as part of “the office,” so they fall outside whatever routine covers the main washrooms. But a shower is the one fitting in a typical office that reliably turns water into a fine, breathable mist — and a shower used twice a week is precisely the warm, low-flow outlet that lets bacteria settle in.
The fix: list every shower in the building, including the ones tucked behind the bike store. Flush the low-use ones on a set schedule, and clean and descale the heads and hoses periodically so they aren’t quietly seeding the spray. Neglected water systems: the danger of stagnation explains why stagnation, not contamination from outside, is usually the root cause.
Assuming the managing agent has it covered
What it looks like: a multi-let building where the tenant assumes the landlord handles all of it, and the landlord assumes their remit stops at the common parts.
Why it happens: responsibility genuinely is split, and rarely written down clearly. The landlord typically controls the incoming main, the cold water storage and the risers; the tenant often controls the pipework and outlets within their demise. HSE’s position is that whoever has control of the premises or the water system carries the duty — and that outsourcing the work to a contractor does not outsource the accountability [2][3].
The fix: get the demarcation in writing. Confirm who assesses, who flushes, who monitors temperatures and who holds the records for each part of the system, from the tank in the basement to the tap on your floor. A boundary nobody has agreed is a boundary where control falls through.
Treating the last fit-out as finished
What it looks like: desks move, a partition goes in, a kitchenette gets relocated — and the old water supply to the old position is capped off rather than removed.
Why it happens: capping a pipe is quick and cheap during a churn; removing it back to the live main is neither. The capped section becomes a dead leg: a length of pipe with water in it that no longer flows anywhere. Offices accumulate these every time the floor plan changes.
The fix: update the schematic and the risk assessment after any works, and treat redundant pipework as something to remove, not cap. If you only inherited a building and don’t know what’s behind the panels, a dead-leg survey is worth more than another sample.
Forgetting the drinks and the kitchen
What it looks like: plumbed-in boiling-water taps, under-counter water coolers, ice machines and the sinks in a rarely-used kitchenette on a far floor — none of them on the asset register.
Why it happens: they feel like appliances, not water systems. But they are outlets on the same supply, and the quiet ones on lightly-used floors carry the same low-flow problem as everything else.
The fix: put them on the list, service them to the manufacturer’s instructions, and make sure far or low-use kitchen taps get run through with the rest of your flushing routine.
Panicking about the air conditioning while ignoring the taps
What it looks like: a flurry of worry about “the AC spreading Legionella” while the unused tap on floor five never gets a second thought.
Why it happens: people conflate all cooling with cooling towers. Most modern offices run closed comfort-cooling or split systems that don’t aerosolise water and aren’t the everyday concern — your domestic hot and cold water is. The real exception is genuine evaporative cooling towers or condensers, which are a recognised higher-risk system and are notifiable to the local authority [4]. If your building has one, it needs proper attention in its own right. If it doesn’t, don’t let tower-anxiety distract you from the still water in the pipes you do have.
The one correction worth making first
If you change a single thing, tie your flushing and monitoring to how the building is actually occupied rather than to a generic weekly tick-box. Map the outlets that get little or no use — the spare floor, the cyclists’ shower, the far kitchenette — and give them a named owner and a set frequency. Everything else in an office is downstream of getting that right.
Write down the reasoning, not just the task. “This shower is flushed weekly because it’s used roughly twice a week; a missed flush escalates to the office manager” is worth far more in an inspection, or after an incident, than a column of initials. Solid record-keeping is what turns routine effort into demonstrable control — Legionella logbooks: an introduction to record keeping covers how to keep logs that actually stand up.
A word on limits
This is general guidance, not a control scheme for your building. The right flushing frequency, the temperature targets you aim for, and where and how often you sample all depend on your layout, your occupancy and who uses the place — a schedule copied from another office won’t fit yours, and the figures should follow your assessment rather than a number borrowed from an article [5]. Use this to ask sharper questions of whoever holds your duty, and to commission a competent, site-specific risk assessment if you don’t already have a current one.
FAQ
Does a half-empty hybrid office need more Legionella attention, not less?
Often yes. Lower headcount usually means more outlets sitting unused for longer, which is the condition Legionella favours [1]. Fewer people in the building doesn’t reduce the risk on its own; it can quietly increase it unless your flushing keeps up with which areas are now idle.
In a multi-tenant office, is it our responsibility or the landlord’s?
Both can hold duties, for different parts of the system. Control generally tracks ownership of the water system: the landlord for shared tanks and risers, the tenant for pipework within their demise. The practical step is to get that split agreed in writing so nothing falls between you, because the duty doesn’t disappear just because it’s shared [2][3].
Do office water coolers and boiling-water taps count?
Yes. They are outlets on your water system, not separate appliances exempt from control. Service them per the manufacturer’s guidance and include the low-use ones in your flushing and monitoring rather than leaving them off the asset list.
Sources
[1] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm [2] HSE, “Legionella and landlords’ responsibilities”. https://www.hse.gov.uk/legionnaires/legionella-landlords-responsibilities.htm [3] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [4] HSE, “Other duties: RIDDOR and notification of cooling towers or evaporative condensers”. https://www.hse.gov.uk/legionnaires/what-you-must-do/duties.htm [5] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm