A refurbishment is the moment your water system stops matching the system your risk assessment describes. A wing gets sealed off behind hoarding. Showers are capped while a bathroom is gutted. The calorifier serving the works area goes cold for a fortnight. Meanwhile a contractor is installing new pipework that sits full of static water, waiting on a handover date that keeps slipping. Each of those is a Legionella decision, and the convenient choice on site is rarely the safe one.
The decision that matters most is what to do with the parts of the system that fall out of use, and how to bring them back. Get that wrong and you finish the project with hidden dead legs, a wing full of stagnant warm water, and no records to show any of it was controlled.
The decision a renovation forces on you
When a branch, a floor or a single outlet stops being used during works, you have a choice. You can keep it live and flush it, you can drain it down and isolate it, or you can cut it back and remove it. People tend to default to whichever is least hassle this week, which is usually “leave it and we’ll deal with it later”. Later is when it bites.
Four things separate a good choice from a lazy one:
- The residual risk it leaves — how much stagnant water stays in the system between now and reoccupation.
- The proof it produces — whether the approach generates records a responsible person can actually point to.
- The recurring effort — labour spent every week the area is offline, versus a one-off job.
- Permanence — whether the works are a chance to delete a problem for good, or just to park it.
A refurbishment is unusual because the third and fourth points swing hard in your favour. The system is already drained, walls are open, and a plumber is on site. Removing a redundant dead leg properly is cheap now and expensive forever after.
Three ways to handle pipework that goes out of use
Match the approach to how long the branch is offline and whether it has a future. The table below is the decision in one view.
| Option for the idle branch | Residual stagnation risk | Effort and the proof it gives you | Sensible when |
|---|---|---|---|
| Leave connected, flush on a set schedule | Highest — warm, still water sits in the branch between every flush | Recurring labour each week it is offline; per-outlet flush records prove control only if they are actually kept | The shutdown is short and the outlet returns to normal use soon |
| Drain down and isolate at the branch | Lower, but a drained line can still hold residue, and it refills into a disturbed system | One-off drain and valve closure now; record the isolation and a written plan to recommission before reuse | The area is offline for weeks to months but will definitely come back into service |
| Cut back to the main and remove the dead leg | Lowest — the reservoir is deleted, not managed | A plumbing change while access is open; then update the schematic and the risk assessment | The outlet or branch is genuinely redundant once the works are done |
The trap is the “temporary” cap. A spur capped a few centimetres past the tee leaves a stub of dead water permanently joined to a live main — a textbook dead leg that outlives everyone who remembers why it is there. If you must cap, cap as close to the tee as the fitting allows, and record that it exists so it does not vanish from the as-built drawing.
Which approach fits which job
Short shutdowns of outlets that will be back in days suit flushing, provided someone owns the schedule and logs it. The risk here is never the water; it is the missed flush nobody recorded, which is the failure pattern behind a lot of record-keeping problems.
Longer phased works — a floor offline for two months while it is stripped and refitted — are where drain-and-isolate earns its place. You stop flushing a branch you cannot easily reach, but you commit, in writing, to recommissioning it before a single tap is used again. The isolation is only safe if the plan to undo it is real.
Whenever an outlet, a shower room or a length of pipe is not coming back, treat the refurbishment as the opportunity it is and remove it. Legionella multiplies in standing water that drifts into the warm-but-not-hot band; general guidance puts growth as limited below around 20°C and the bacteria as progressively killed above around 60°C [1]. A branch you have deleted cannot drift into that band at all — the only option here that lowers risk for good rather than asking someone to keep managing it.
Bringing it back: recommissioning before anyone showers
New and altered pipework is not safe simply because it is new. It arrives exposed to debris, swarf and jointing compound, it may be pressure-tested with water that then sits static for weeks, and it joins a system that has been disturbed, drained and refilled. Sediment stirred up by the works gives bacteria something to feed on.
So the handover is not “turn the valves back on”. Guidance generally expects new or modified systems to be cleaned, disinfected and flushed before they are brought into use [2], and the same logic applies to any branch you drained and isolated. Before the area reopens, flush it through every outlet, confirm hot water reaches temperature and cold water stays genuinely cold at the furthest tap [3], and decide with your risk assessor whether sampling adds anything. Sampling can support verification after major works, but the frequency and the trigger follow the risk assessment, not a fixed rule [4].
The other half of recommissioning is paperwork. A refurbishment that moves pipework, changes how a space is used, or alters who occupies it is a material change to the system, and the code of practice for these assessments expects a review when that happens [1][5]. Update the schematic to match what was built, not what was drawn, and write the review while the works are fresh — the person who reopens the wing in a year will only know what the records tell them.
A fair caveat for refurbishment work
This is general guidance, not a control scheme for your building. A single bathroom refit and a phased hospital ward strip-out share almost nothing except the word “renovation”, so the temperatures, dwell times, disinfection method and sampling decisions for yours have to come from a competent, site-specific assessment. Treat any figure here as a prompt to check your own scheme, not a number to copy. If the works touch a higher-risk system such as a cooling tower or evaporative condenser, the controls and notification duties for those sit outside a general hot-and-cold refurbishment and need specialist input.
What to do before the contractor isolates anything
Before the first valve is closed, walk the scope with your schematic and a marker. For every outlet and branch in the works area, decide now whether it gets flushed, drained or removed, and write that decision against it with who owns the task and what proves it was done. Record the reasoning, not just the action: “Third-floor showers drained and isolated for the duration; clean, disinfect and flush before the floor reopens; risk assessment reviewed at handover.” Do that across the scope and the refurbishment ends with a system you can account for, not a set of surprises waiting in the walls.
FAQ
Does new pipework need treating before we use it, or is it clean because it’s new?
It needs treating. New pipe is exposed to debris, flux and jointing compound during installation, and often sits full of static or test water for weeks before handover. Guidance generally expects new and altered systems to be cleaned, disinfected and flushed before use [2] — build that step in rather than assuming “new” means “safe”.
We’re only refurbishing one floor — do we need to revisit the whole Legionella risk assessment?
Probably, at least in part. Moving pipework, changing how a space is used, or changing who occupies it is a material change to the system, and the code of practice for these assessments expects a review after significant changes [1][5]. A focused review of the affected area and any shared risers usually suffices — but write it up and update the schematic to match what was built.
The contractor is managing the water system during the works — are they responsible for Legionella, or are we?
The duty holder — the organisation in control of the premises — keeps the responsibility, including oversight and records [6]. A contractor carries out tasks under that duty; handing them the spanners does not hand over accountability. Spell out in the contract exactly who flushes, who isolates, who recommissions and who records each, so nothing falls into the gap between the two parties.
Sources
[1] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems — Approved Code of Practice and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [3] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm [4] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm [5] BSI, “BS 8580-1:2019 — Risk assessments for Legionella control. Code of practice”. https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1 [6] HSE, “Legionnaires’ disease — what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm