What temperature should your water heater be set to?

The Department of Energy and most safety bodies recommend 120 degrees Fahrenheit. Water heaters are frequently shipped set to 140, which costs meaningfully more in standby heat loss and creates a real scald hazard, since water at 140 can cause a third-degree burn on adult skin in roughly five seconds and far faster on a child's thinner skin. Scald injuries from tap water send thousands of people, disproportionately young children and older adults, to emergency rooms each year. Dropping to 120 typically saves a modest but real amount annually on the water heating portion of a utility bill, which is usually the second largest energy use in a home.

There is a genuine counterargument worth knowing rather than dismissing. Legionella bacteria can grow in water below roughly 122 degrees, and public health guidance in some contexts recommends storing water hotter and using thermostatic mixing valves at fixtures to deliver it safely at the tap. That approach is standard in healthcare and increasingly recommended for households with immunocompromised or elderly residents. For a typical household with young children, 120 is the reasonable default. Check the actual delivered temperature with a thermometer at a tap rather than trusting the dial, which is often inaccurate, and run the water a couple of minutes first. If you leave for an extended period, most units have a vacation setting, and flushing the lines on return is a sensible habit.