The recommended temperature setting for most water heaters is 120 degrees Fahrenheit. The United States Department of Energy recommends this temperature setting to save energy and reduce the chance of scalding injuries.
While many water heater manufacturers set a default temperature of 140 degrees Fahrenheit on their products, the Department of Energy estimates that setting a water heater's thermostat to 120 degrees saves over $400 per year. However, some types of dishwasher require a higher setting of 130 to 140 degrees for proper operation. Persons with compromised immune systems or significant respiratory problems are also advised to maintain a setting of 140 degrees on their water heater thermostat to reduce the risk of legionellae bacteria growth in the heater's tank.