The Hidden Legionella Risk Lurking in Empty School Buildings This Summer

Six weeks of summer holidays sounds like a well-earned rest for staff and pupils. For a school's water systems, it's something closer to the opposite. Empty buildings, reduced usage and warm weather create exactly the conditions Legionella bacteria need to establish themselves, and the risk doesn't announce itself until taps are turned back on in September.

Because schools are workplaces, they fall under the Health and Safety at Work Act 1974, which requires management to ensure staff and pupils aren't exposed to Legionella bacteria. The Health and Safety Executive sets out how to meet that duty through its Approved Code of Practice L8 and the accompanying technical guidance, HSG274, with Part 2 being the section most relevant to the domestic-style hot and cold water systems found in almost every school building.

Getting legionella risk management wrong over the summer doesn't just create a compliance problem, it creates a genuine health risk for the first people back through the door.

Why Empty Buildings Are a Legionella Risk Factor

Legionella bacteria thrive in warm, stagnant water, and multiple sources in the water hygiene sector consistently cite the same danger zone: legionella thrives between roughly 20°C and 45°C. A school over the summer holidays ticks every box for that range. Showers in PE changing rooms go unused, science lab outlets sit idle, staff facilities see a fraction of their normal traffic. Water that isn't moving through a system doesn't just sit there quietly, it becomes a breeding ground, and outlets used regularly during term time can be left unused for weeks over summer, encouraging exactly the stagnation that allows Legionella to develop.

This is precisely why a legionella assessment carried out before the holidays begin is worth far more than one carried out after something's gone wrong. Identifying which outlets are likely to fall into disuse gives facilities teams the chance to build a monitoring plan around them, rather than discovering the gaps in September.

Start With the Risk Assessment, Not the Checklist

It's tempting to treat summer legionella preparation as a box-ticking exercise, print off a checklist, work through it, file it away. But the checklist only works if it's built on a risk assessment that's current and accurate. HSG274 Part 2, paragraphs 2.50 to 2.52, set out how buildings that have been temporarily taken out of use, sometimes referred to as mothballing, should be managed so that microbial growth, including Legionella, remains appropriately controlled. If your assessment predates that kind of scheduled, intermittent-use planning, or if anything about the water system has changed since it was last reviewed, whatever monitoring you do over the summer is being built on outdated information.

This is where independent legionella consultants add real value. A fresh set of eyes on the risk assessment, ideally from a legionella specialist not involved in day-to-day site management, tends to catch the drift that happens gradually over a school year: a new outlet added here, a section of pipework isolated there, none of it dramatic on its own, but collectively enough to change the risk picture.

The Non-Negotiables Over the Break

Whatever else changes term to term, a few fundamentals shouldn't.

Flushing. Good water management focuses on ensuring sufficient water turnover to prevent stagnation. The general guidance is that infrequently used outlets, those used less than once a week, should be flushed at least weekly, with higher-risk premises requiring more frequent flushing than that. The right frequency for any individual outlet still depends on what the risk assessment says for that specific site.

Temperature control. HSG274 Part 2, paragraph 2.6, sets out the benchmark: cold water at the outlet must stay below 20°C, and hot water must be stored at 60°C or above and delivered at no less than 50°C at the outlet, including at any point-of-use water heaters on site. These aren't arbitrary numbers, they're the boundary outside of which Legionella struggles to establish itself, and letting either drift during a quiet summer is one of the most common ways schools end up with a problem in September.

Records. It isn't enough to carry out flushing and temperature checks, they need to be documented. Under HSG274, paragraph 25, monitoring and inspection records must be kept for at least five years and made available for inspection by the HSE or local authority if required. When something does go wrong and September testing turns up an issue, that paper trail is what demonstrates a school met its duty of care rather than got lucky.

Reopening Is Part of the Process, Not an Afterthought

The final piece of legionella risk management over summer often gets the least attention: what happens in the days before term starts again. Records from across the break need reviewing, not filing. Systems that were isolated or run at reduced capacity need proper recommissioning, not just switching back on. And where there's any doubt about how well flushing and temperature control held up, that's exactly the point at which legionella sampling in higher-risk areas earns its cost many times over compared to the alternative.

It's also worth noting that for longer periods of disuse it can be acceptable to leave a system filled with water without weekly flushing, provided measures are in place to prevent unauthorised use, although this does increase the opportunity for biofilm to establish itself. That's a judgement call for a risk assessment to make on a site-by-site basis, not a shortcut to assume by default.

Getting Support Before September

Compliance monitoring across a six-week closure is a lot to hold together alongside existing staff workload, particularly for schools without a dedicated facilities team. This is exactly the gap that independent legionella consultants are designed to fill: reviewing whether an existing risk assessment still holds up, building a realistic flushing and monitoring plan around a specific site's outlets, and being on hand for sampling if reopening throws up any doubts.

At ISHEM, we provide independent, expert support for schools and public sector clients across the UK, Ireland, Europe, APAC and North America, from risk assessments through to advising on control programmes. If you'd like help getting ready before the summer break begins, get in touch at support@ishem.com, or call 01675 466360.