How Climate Change and Water Stress Are Reshaping Legionella Risk Management

The Environment Agency projects that England faces a public water supply shortfall of close to five billion litres a day by the middle of this century, a figure repeated consistently across government and industry sources over the past two years. At the same time, recent years have brought some of the warmest and, at points, wettest periods on record. For most people, these read as abstract environmental statistics. For anyone managing a water system, they're anything but: they directly affect how hard it is to keep water moving and systems consistently within a safe temperature range, and that has a direct bearing on legionella risk.

Why Climate Change Is Becoming a Legionella Risk Factor

Legionella bacteria thrive in water between roughly 20 and 45 degrees Celsius, which is exactly the range that becomes harder to avoid as average temperatures rise. Warmer ambient conditions push cold water systems closer to that danger zone for longer periods of the year, while more variable rainfall patterns and periods of drought can affect water quality and pressure in ways that complicate an already delicate balance.

This matters most for sites already managing challenging infrastructure, where complex pipework, dead legs and poor water system designs give bacteria more opportunity to establish themselves even before climate is factored in. A control regime that comfortably managed risk a decade ago may need a harder look now, simply because the baseline conditions it was designed around have shifted.

The UK's Growing Water Stress Problem

The scale of the pressure on UK water supply infrastructure isn't a fringe concern. It sits at the centre of the government's wider water reform agenda, which has set out plans for new reservoirs, desalination schemes and demand reduction measures to close the projected gap between supply and demand. The Environment Agency's National Framework for Water Resources has been explicit that, without further action, the shortfall equates to more than a third of the water currently available for public supply.

This connects directly to the broader Net Zero and sustainability planning that many estates teams are already engaged with. Water security is increasingly treated as a resilience issue alongside energy and carbon, and legionella risk management sits squarely within that picture rather than as a separate compliance workstream. For the full detail behind these figures, the Environment Agency's National Framework for Water Resources 2025 sets out the scale of the shortfall and the action being taken to address it.

What This Means for Your Legionella Risk Management Approach

This is where the wider trend needs to translate into something practical. A handful of questions are worth asking of any current risk management approach:

• Does your risk assessment account for seasonal temperature variability, or was it written around average conditions that no longer reflect what a system experiences during an extended warm spell?

• Does monitoring frequency flex during periods of higher risk, such as prolonged warm weather, or does it stay fixed to a standard schedule regardless of conditions?

• How well does your control programme account for intermittent occupancy? Hybrid working patterns mean many buildings still see less consistent use than they did before 2020, and periods of low or no occupancy remain one of the more reliable ways for stagnation, and therefore risk, to build up in a system, climate pressures aside.
  

None of these questions require abandoning an existing legionella control management programme and starting again. They're about testing whether the assumptions it was built on still hold, given that the conditions systems now operate under are measurably different from when many control schemes were first written.

Building Climate Resilience into Your Water Safety Plan or Written Control Scheme

Water safety plans and written control schemes are sometimes treated as static documents, reviewed on a fixed cycle and otherwise left alone. That approach sits increasingly awkwardly with a climate baseline that's shifting within that same window.

A resilience-focused review looks beyond a single point-in-time check and instead at trends: how temperature monitoring data has moved over recent months and years, rather than whether the most recent reading happened to fall within range. It also means building in enough flexibility to respond to an unusually warm or dry period without waiting for the next scheduled review to catch up. Practically, this can be as straightforward as:

• Reviewing temperature logs for gradual upward drift, not just individual out-of-range results.

• Building a trigger into the plan for additional monitoring during sustained warm weather, rather than treating it as a one-off exception.

• Making sure the plan itself is revisited whenever occupancy patterns change materially, rather than only at the scheduled review point.
  

This is closely tied to the wider water management approach a site takes, and it's often most effective when reviewed alongside that documentation rather than as a standalone exercise.

Sectors Where This Matters Most Right Now

While the trend affects every duty holder, it plays out differently depending on sector:

• Healthcare carries the highest stakes, given the vulnerability of many occupants to legionella infection, and the least tolerance for any lapse in control.

• Education already contends with known seasonal occupancy challenges, particularly over summer closures, which now overlap more directly with the warmest and highest-risk periods of the year.

• Leisure and hospitality, especially sites with spa pools and cooling towers, face particular exposure during hot weather, when both demand on systems and ambient risk factors peak simultaneously.

  
  

Planning Ahead of the Next Heatwave

Water stress and rising temperatures aren't a one-off event to plan around and then set aside. They're a trend, and the organisations best placed to manage it are the ones building resilience into their risk management approach now, rather than reacting after a temperature excursion has already occurred.

If you'd like support reviewing your water safety plan or written control scheme with climate resilience in mind, or want to discuss ongoing monitoring options, get in touch with ISHEM.