Why Legionella Risk Increases in Summer & How to Prevent It
We all love summer right? The weather is warmer, we dig out our summer clothes and we are overall happier. However, did you know that during summer, and particularly during heatwaves (like the ones we have been getting lately), the danger of legionella in your water systems is significantly higher?
Having legionella in your water system isn’t always caused by bad hygiene. Legionella thrives in warm water, mostly between 20c – 45c. During summer outdoor temperatures can push cold water systems above safe levels. In particular this happens in underused buildings or poorly insulated pipework.
Add to that reduced building occupancy (common during summer holidays or shutdowns), and you’ve got a perfect storm for water stagnation. Taps, showers, and tanks that sit unused for days or weeks allow water to sit still and warm up. A direct invitation for Legionella to multiply.
Common Hotspots to be aware of
Some areas are more vulnerable than others during the summer:
Cold water storage tanks located in warm lofts or poorly ventilated plant rooms
Dead legs or rarely used outlets, like outside taps or spare showers
Irrigation systems, hose reels, and garden features using stored water
Cooling towers and evaporative condensers, especially if maintenance is irregular
By identifying these hotspots early, you can take simple, proactive steps to stay in control.
What Action You Can Take Now
The good news? You don’t need to overhaul your entire system to manage summer risks. A few targeted actions can make a big difference:
Flush outlets regularly – especially in low-use areas or during building closures
Check and record water temperatures – make sure cold stays below 20°C and hot hits 60°C
Review your risk assessment – summer-specific reviews help spot seasonal vulnerabilities
Insulate tanks and pipes – protect them from ambient heat gain
Clean and disinfect water systems if stagnation is suspected
Test water for Legionella more frequently during hot spells, especially in high-risk environments
These simple routines don’t just reduce Legionella risk, they also demonstrate clear due diligence if something does go wrong.
Get a Summer Strategy
So many organisations treat Legionella prevention as a “set and forget” process. However, water systems are dynamic. Seasons change, and so do risks. The last few years our summers have been unpredictable with sudden heatwaves and much higher temperatures. Having a strong summer strategy shows you are thinking ahead of these changes and taking the safety of your building and occupants seriously.
Let’s not forget about Legionnaires disease. It is a fatal form of pneumonia in older and vulnerable occupants. However with the right measures in place, it can be completely preventable.
Conclusion
Summer doesn’t need to catch you off guard. With proper planning, regular checks, and expert support, you can keep your water systems safe year-round. If you’re unsure where to start or need help reviewing your Legionella controls this summer, get in touch with the ES Water Solutions team. We’re here to help you stay compliant, and more importantly, safe.