--- title: "Legionella and site welfare on construction sites" source_url: https://legionella.io/articles/legionella-and-site-welfare-on-construction-sites/ canonical_url: https://legionella.io/articles/legionella-and-site-welfare-on-construction-sites/ pillar: "Building Types & Use Cases" summary: "Temporary welfare units, intermittent supply and CDM duties make site water a real Legionella risk. A flushing routine and checklist that holds up to an audit." primary_keyword: "construction site Legionella" date_published: 2026-02-24 date_reviewed: 2026-06-26 author: "Legionella.io editorial team (REMOTE TECH LTD)" reviewed_against: "HSE L8 and HSG274 guidance" region: "United Kingdom" license: "(c) REMOTE TECH LTD. Quote freely with attribution and a link to source_url." --- # Legionella and site welfare on construction sites Site welfare water is risky for one boring reason: it sits still. Temporary cabins, jackleg toilets and drying-room showers get used hard at 7am, then nothing happens to that water until the next shift. Over a weekend, a shutdown or a quiet phase, warm pipework in a heated cabin becomes exactly the standing reservoir Legionella needs. The thing that catches contractors out is ownership. On a CDM project the duty to assess and control Legionella sits with whoever controls the system, and on a live site that is usually the principal contractor, not the welfare-hire firm who dropped the units and drove off [1][4]. The cabins are temporary. The duty is not. So the core principle is simple, and the rest is how to apply it. Water that is not used must be deliberately moved, by someone whose job it is, with a record that proves it happened. ## The principle, applied to four situations you actually face ### The Monday-morning cabin after a quiet weekend Friday's last use is the kettle and the wash basins. The site shuts. The cabins stay heated for frost protection, sometimes two days, sometimes four over a bank holiday. Cold-water pipes run warm against a hot calorifier, the stored hot water cools into the range Legionella likes, and nothing flushes any of it. The pragmatic call is to treat every outlet unused beyond about a week as one to flush, and to flush hard before reuse after any longer stand-down. As a general expectation, infrequently used outlets are turned over weekly, with the exact frequency set by your site risk assessment rather than a number off the internet [2]. On a five-day site that mostly means a documented first-thing flush on the Monday after a long weekend: run every tap and the shower until the temperature stabilises, then log it. Showers matter most because they throw the breathable aerosol that carries the bacteria into the lungs [3]. ### The drying-room shower nobody used for a fortnight Welfare showers get fitted because the regs and the workforce expect them, then sit idle on a job where nobody gets muddy enough to bother. An idle shower is the worst case on site: warm water, a stagnant dead leg up to the head, and a fine spray the moment someone turns it on. If a shower genuinely is not being used, the honest options are to flush it weekly under a written routine or to take it out of service properly: cap the supply close to the live pipe and remove the dead leg, not just hang an out-of-order sign on a unit that still holds water. Flush it long enough to clear and reach temperature, ideally with the head removed or held low to limit the aerosol while you do it [2][3]. ### The emergency safety shower that is never meant to run Sites with concrete, chemicals or hot works often have an emergency drench shower or eyewash. By design it is never used, which makes it a permanent dead leg holding warm, still water that someone may one day put straight onto their eyes and skin. This is the outlet people forget precisely because using it is the exception. It still needs weekly activation, run to flush the standing volume, recorded the same as any other. An emergency shower full of stagnant water is a Legionella source pretending to be a safety device. ### Intermittent supply: mains that comes and goes, or a bowser Temporary supply is rarely steady. The mains connection arrives late so early welfare runs off a bowser or static tank; the supply gets isolated for groundworks; pressure drops as the site grows. Every interruption is a chance for warm, still water to sit in storage and in the run to the cabins. Keep stored water moving and keep it cold. A bowser standing in summer sun warms quickly, so size storage to a few days' real use rather than a fortnight's, turn it over, and keep it covered and clean. When mains is isolated and recharged, treat the recharge like a small recommissioning: flush the affected outlets before anyone drinks or showers. The general control targets still apply on site, stored hot water kept hot and cold water genuinely cold, with the figures your scheme sets [2]. The same standing-water logic runs through renovation work; [Managing Legionella risk during building renovations](https://legionella.io/articles/managing-legionella-risk-during-building-renovations/) covers it on the building side, and [Temporary events and festival sites: portable water systems](https://legionella.io/articles/temporary-events-and-festival-sites-portable-water-systems/) is worth a look for portable and bowser supply. ## The site welfare flushing checklist Group it by frequency, make every line a verb, and make every line recordable. In my view this is the most useful thing to pin inside the welfare cabin: it turns a vague duty into a named weekly job. **When welfare is first set up** - Confirm in writing who owns the water system, principal contractor or hire firm, and name a responsible person. - Record the date water first entered the system and each tank or bowser. - Write the flushing regime into the construction phase plan, not a side note. - Check no shower or tap is fitted that nobody intends to use; remove or cap it if so. **Weekly, by the named person** - Run every tap and shower until the temperature stabilises; log start state and result. - Activate the emergency drench shower and eyewash to flush standing water. - Check stored hot water is reaching temperature and cold water is staying cold. - Confirm any bowser or tank has been turned over and is covered and clean. **After any stand-down, shutdown or supply interruption longer than the set period** - Flush all outlets before reuse, showers last and with aerosol kept low. - Recharge and flush through any isolated section before drinking or washing. - Record the stand-down dates so the gap itself is evidenced, not just the flush. **Ongoing** - Descale and disinfect shower heads on the assessed frequency. - Review the regime when the site phases, grows or the welfare moves. How you record it matters as much as doing it. A laminated sheet on a clipboard goes missing when the cabin moves, gets weather-damaged, or quietly stops being filled in three weeks before an HSE visit. A digital logbook on a phone timestamps who flushed what and flags a missed week before it becomes a gap, which is what an inspector or insurer wants to see. The trade-off is honest: flushing costs labour and water, and on a tight programme it is the first thing to slip. But the cost of a missed routine is a contractor who controlled the system and cannot show they controlled the water [4]. This is general guidance, not a site-specific control scheme. Temporary welfare varies enormously, from a single jackleg toilet to a multi-storey modular complex, and the flushing frequencies, temperatures and out-of-service decisions for your site come from HSG274 and a competent person who has seen your welfare layout and supply, not from a template. The concrete next step: this week, walk your welfare, find the one outlet nobody has used in a fortnight, and put a name and a weekly date against it. That orphaned shower or eyewash is where your site risk is sitting right now. ## FAQ ### Who is responsible for Legionella in temporary site welfare, us or the hire company? Whoever is in control of the system on site, which on most CDM projects is the principal contractor running the welfare day to day, not the firm that delivered the units [1][4]. The cleanest approach is to settle it in writing in the hire contract and the construction phase plan, name a responsible person, and not assume the duty left site with the delivery driver. ### How often should we flush welfare units that are barely used? Treat infrequently used outlets as weekly flushing as a general expectation, with the precise frequency set by your site risk assessment rather than a fixed rule [2]. After a long weekend, a shutdown or any supply interruption, flush before reuse regardless of the routine, and pay particular attention to showers because of the aerosol they create [3]. ### Do we need to worry about water that has only stood over a weekend? A heated cabin keeps pipework warm, so two or three still days is enough for water to sit in the range that favours growth. It rarely needs special treatment beyond a proper first-thing flush of every outlet on the Monday, logged, with showers run until the temperature stabilises [2][3]. ## Related reading - [Temporary events and festival sites: portable water systems](https://legionella.io/articles/temporary-events-and-festival-sites-portable-water-systems/) - [Managing Legionella risk during building renovations](https://legionella.io/articles/managing-legionella-risk-during-building-renovations/) - [Commissioning new water systems: preventing Legionella from day one](https://legionella.io/articles/commissioning-new-water-systems-preventing-legionella-from-day-one/) ## 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, "Systems most likely to create legionella risk". https://www.hse.gov.uk/legionnaires/risk-systems.htm [4] HSE, "Legionnaires' disease - what you must do". https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm