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The Impact of Cold Water Systems in Hot Weather

“With the weather improving over the last couple of weeks and as we move into summer, it’s worth thinking about the impact hot weather can have on water systems and temperature monitoring”


Roll on the warm, and hopefully hot British summer months…

When  conducting temperature monitoring, please pay close attention to the temperatures of cold water in hot weather – temperatures above 20oC can lead to increased risk of bacteria growth, inclusive of Legionella.

If in carrying out your role, you identify a series of temperatures above 20oC on domestic water systems, please make sure that you raise this as a non-conformance within your internal control systems (including your Legionella Log Book), as it is a strong indicator of problems with systems in terms of design, insulation, etc, likely leading to heat transfer.

With ‘hot’ cold water it is often though acceptable to just ‘check again next month’ as the issue will normally be linked directly to weather, which by its nature is changeable. If you identify an incidence of ‘hot’ cold water when carrying our your temperature monitoring, it can be valid to engage in precautionary Legionella sampling, along with any other sitespecific measures which could be taken to reduce the warming of water such as improving lagging or increasing flushing of outlets, as the issue is likely to reoccur every time there is a spell of hot weather.

Key Takeaway

If you find any significant examples of ‘hot’ cold water when conducting temperature monitoring tasks, please discuss within your Legionella management pathway to agree the best way forward in terms of resolution or risk control. By doing this you can reduce risk for your colleagues and anyone else who uses your buildings.

Ed Williams
Quality, Health, Safety and Environment Manager,

Hydro-X Water Treatment,
Part of the Hydro-X Group

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