Basic Rules to prevent the proliferation of Legionella
Hot water must be stored at a high temperature, as a precaution against bacteria*. It can be delivered from the tap at a lower temperature to prevent scalds.
The (terrestrial) solution to the temperature dilemma, is to use a quality mixing valve, to allow VERY hot water to go to the dish washer and laundry
machines to actually kill GERMS, and use these tempering valves to control the temperature of the water, after these devices to go throughout the system.
Now when this hot water reaches a shower
or faucet, you can add safety
devices called pressure/temperature regulating/valves, or balancing valves, etc. What these devices do is protect the user from being scalded, when someone else flushes a toilet, and the pressure drop is acted upon, with no chance of the user being burned.
* For example, temperatures under 50 C may increase the risk of Legionnaires’ disease, a form of pneumonia, due to bacterial growth in the tank. That disease is caused by Legionella bacteria, which live in water. Temperature is a critical factor for Legionella to grow. The risk of colonization in hot water tanks is significant between 40 and 50 C
. Drinking contaminated water is not a major cause of Legionnaire’s disease.
Water temperatures are critical:
Keep cold water below 20̊C (68̊F) maximum
Keep stored hot water above 60̊C (140̊F) minimum
Keep the return temperature of a secondary return system above 50̊C (122̊F) minimum
Legionella thrives in warm environments 25 to 45 ̊C (77 to 113 ̊F).
According to Reliance WorldWide:
Temperature affects the survival of Legionella are as follows:
* 70 to 80 ̊C (158 to 176 ̊F): Disinfection range
* At 66 ̊C (151 ̊F): Legionellae die within 2 minutes
* At 60 ̊C (140 ̊F): Legionellae die within 32 minutes
* At 55 ̊C (131 ̊F): Legionellae die within 5 to 6 hours
* Above 50 ̊C (122 ̊F): They can survive but do not multiply
* 35 to 46 ̊C (95 to 115 ̊F): Ideal growth range
* 20 to 50 ̊C (68 to 122 ̊F): Legionellae growth range
* Below 20 ̊C (68 ̊F): Legionellae can survive but are dormant