Water heaters should be set to 120 to 125 degrees Fahrenheit as a precaution against scalding and to maximize energy efficiency. Some manufacturers recommend setting water heaters to 140 F. However, this temperature can result in unnecessary standby heat losses and creates a risk of burns.
Water heated to above 125 F can cause severe scalds in less than two minutes. The average water temperature used in a shower or washing machine is 110 to 115 F, meaning it is usually unnecessary to heat water to a high temperature. However, dishwashers require 130 140 F water, so it may be necessary to set the water heater to a higher temperature.
Households with small children may wish to set their water heaters to below 120 F to further protect against accidental scalds. Conversely, because water heaters set to 120 F carry a very small risk of promoting legionellae bacteria growth, immunosuppressed individuals may need to set their water heaters to 140 F.