How hot should shower water be? The 120°F line

Where 120°F comes from

Most water heaters can be set well above what a shower needs. The US product safety agency has a clear view on where to set yours.

The U.S. Consumer Product Safety Commission (CPSC) urges all users to lower their water heaters to 120 degrees Fahrenheit.

U.S. Consumer Product Safety Commission, Avoiding Tap Water Scalds (Publication 5098). Read 28 September 2026.

Lowering the setting is a one-time job on the heater itself. Your shower valve can only mix what the heater gives it, so this is the setting that limits every tap in the house.

Hot water burns faster than people expect

Scalds are about time as well as heat. At high settings, a few seconds is enough, and even 120°F is not harmless if someone cannot move away from it.

Even if the temperature is 120 degrees, a five minute exposure could result in third-degree burns.

U.S. Consumer Product Safety Commission, Avoiding Tap Water Scalds (Publication 5098). Read 28 September 2026.

That is why the people most at risk are those who cannot react quickly: small children in a bath, and older relatives in a shower.

Test first, every time

The simplest habit is still the most useful one.

Always hand-test before using, especially when bathing infants and young children.

U.S. Consumer Product Safety Commission, Avoiding Tap Water Scalds (Publication 5098). Read 28 September 2026.

A light on the shower head does not replace that habit. It gives you a warning before your hand gets there, which is most useful when someone else used the shower last or the heater has just come back up to temperature.

What the FASTRAS colors tell you

• Green: below 85°F. Still cool, the hot water has not arrived yet.
• Blue: 85 to 105°F. The comfortable range for most showers.
• Red: 105 to 120°F. Hot. Check before a child goes under.
• Flashing red: above 120°F. Turn the mixer toward cold.

The light reacts to the water, it does not control it. If you see flashing red often, the fix is the setting on your water heater, not the shower head.