October 2026

What the UK's recent high temperatures mean for Legionella control

The UK experienced prolonged periods of unusually high temperatures this summer, bringing heatwaves, warm nights, and increased pressures on building water systems across the country.

Whilst many people welcomed the sunshine, warmer conditions can create challenges for those responsible for managing water hygiene and Legionella risk.

At Water Environmental Treatment (W.E.T.), we observed a noticeable increase in the number of confirmed Legionella-positive samples during the hottest periods of the year.

Although each water system is unique, the trend serves as an important reminder of how quickly conditions can change when temperatures rise.

Why does hot weather matter?

Legionella bacteria thrive within a temperature range of approximately 20°C to 45°C. During warmer weather, maintaining cold water temperatures below recommended thresholds can become more difficult, particularly in:

Cold water storage tanks
Large building distribution systems
Little-used outlets
Pipework exposed to solar gain
Buildings with fluctuating occupancy levels

Even systems that are normally well controlled can face additional challenges when prolonged periods of high ambient temperatures affect incoming mains water and internal building conditions.

A timely reminder for duty holders

The increased number of positive samples identified this summer highlights the importance of remaining vigilant. Regular monitoring, temperature checks, flushing regimes, inspections, cleaning, and risk assessment reviews all play a vital role in maintaining safe water systems.

As climate patterns continue to change and periods of extreme weather become more frequent, organisations may need to consider whether their existing control measures remain suitable for increasingly warm conditions.

Is your water system ready for the next heatwave?

Autumn is an ideal time to review the performance of your water management programme and identify any lessons learned from the summer months.

Whether you manage healthcare facilities, education estates, commercial premises, residential buildings or industrial sites, W.E.T. can help you assess your current controls and strengthen your compliance strategy.