What are the risks associated with hot water?
The short answer
Two, and they pull in opposite directions. Water stored too cool — roughly 20°C to 45°C — lets bacteria such as Legionella multiply. Water delivered too hot scalds, and it does so faster than people expect: at around 60°C, serious burns happen in a matter of seconds, and far quicker on a child's skin. The safe answer is to store hot and deliver blended.
Scalding is the risk that gets underestimated in ordinary homes. It isn't only about the temperature — it's about how fast it happens. Water hot enough to control bacteria in a cylinder is hot enough to burn seriously in seconds, and children, older people and anyone who can't move quickly or feel temperature properly are at much greater risk.
Legionella is the risk in the other direction. It's a bacterium that lives in water systems, multiplies in the warm middle range, and is inhaled in fine spray — a shower being the obvious source. It's rare in a well-run home system, and it's the reason cylinders are kept above 60°C rather than at a comfortable-sounding 40.
The reason both risks can be handled at once is that they're handled in different places: temperature is controlled in the cylinder for bacteria, and at the outlet for skin. Anyone who tells you to just turn the tank down has solved one problem by creating the other.
Got a plumbing job in Macclesfield?
Tell us what you need and it goes straight to our local plumber — one call back, usually the same day. Free quote, no obligation.