One of the concerns with storing hot water at a high enough temperature to kill Legionella bacteria is that it creates a risk for scalding. There is always a balancing act between hot water storage temperatures that prevent Legionella bacteria growth and scalding concerns. Plumbing engineers have recommended hot water storage temperatures in excess of 135 to 140 degrees Fahrenheit to minimize Legionella bacteria growth and they recommend using a master thermostatic mixing valve to mix cold water with the hot water and deliver hot water at 120 degrees or less to minimize the risk of scalding.
More Scalding Information
The scald burn studies done by doctors Moritz and Henriques showed lime-scaled-shower-headthat it took approximately five to eight minutes of exposure to temperatures in the range of 120° Fahrenheit(F) for adults to develop a serious scald burn: Someone exposed to water at 120°F would have approximately five to eight minutes to get out of harm’s way before an irreversable injury started to develop. It should be noted that children and the elderly have skin that is thinner than the adult skin from the Moritz and Henriques studies and could develop burns sooner than five to eight minutes. The 120°F temperature limit has become an industry standard for scald prevention in showers and combination bathtub/showers. The American Society of Plumbing Engineers (ASPE) is nearing completion of a standard on recommended temperature limits for domestic hot water fixtures. The new standard will cover temperature limits for a wide variety of plumbing fixtures. There will be a few fixtures that will have temperature limits below 120°F. The model plumbing codes also limit hot water temperatures in showers, bathtubs, bidets and whirlpool bathtubs