With the latest Building Regulations regarding hygiene and the introduction of thermostatic mixing valves to maintain all hot water outlets at a safe temperature of 43ºC, how exactly is the mixing cold water disinfected from Legionella?

Question from Niall Corr via email:
With the latest Building Regulations regarding hygiene and the introduction of thermostatic mixing valves to maintain all hot water outlets at a safe temperature of 43ºC, how exactly is the mixing cold water disinfected from Legionella?

The hot water has already been disinfected from Legionella by heating it to 60ºC, but to then “blend” it with cold or cool water which hasn’t been disinfected will greatly increase the risk of Legionella at that very temperature range; 25-45ºC.

Response from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
The new Building Regulation’s requirement is that the water temperature obtained from a bath or shower should be at no more than 48ºC. The rest of the house can receive water at the temperature set either on the cylinder thermostat, or to what the combi or water heater temperature delivers at. There is no increased risk of Legionella as the blending is at the point of use.