What should your water heater be set to, and why?

Hard water and your water heater meet at two numbers: CPSC urges a 120°F setting, and hardness drives scale, 9.0 grains on average at the Potomac plant and 4.1 at Patuxent (our arithmetic).

By the Your Water Numbers desk, not WSSC Water · Updated November 2, 2026 · How we check

Reading this: Burn times shorten fast above 120°F. Children under five and older adults make up most of the injuries and deaths, so test the water by hand before a bath.

If you smell gas, what do you do first?

Leave the house first. Don’t touch a switch and don’t use a phone inside. From outside, call 911 and Washington Gas. Don’t go back to check the heater.

How do you check the temperature?

Use a candy or meat thermometer at a faucet. CPSC says to take the reading first thing in the morning, or at least two hours after water use.

If it reads high, here’s who adjusts it:

• Gas heater: ask your gas company or a licensed plumber to set it. We give no steps for the gas control.
• Electric heater: CPSC suggests your electric company. You can switch the breaker off, and our advice stops there. The thermostats sit behind panels near live wiring, so leave those to a licensed person.

CPSC notes that a lower setting also saves energy and money.

How much does your plant’s hardness matter?

More on Potomac water than on Patuxent water. Hardness averages 154 mg/L on Potomac and 70 mg/L on Patuxent in the 2025 tap report. That’s 9.0 and 4.1 grains by our arithmetic, up to 12.5 at Potomac’s high.

USGS ties hard water to scale in pipes and water heaters. We have no local figure for how much scale forms, how much efficiency it costs or how long a heater lasts. Treat any such number you hear with care.

Do you need a softener because of the heater?

Usually not on Patuxent, and not automatically on Potomac. Look at your aerators and showerheads first. If they stay fairly clean, a softener for the heater’s sake is hard to justify. If you’re at the Potomac end and scale keeps coming back, read our hardness page for the numbers before deciding.

For tank flushing, ask a licensed plumber; we give no steps here. We found no official interval that applies to all homes.

What work has to be licensed?

All gas work does, including swapping a gas water heater. In Montgomery and Prince George’s, plumbing and fuel gas work requires a WSSC Water license and insurance. Gas work needs a registered gasfitter, a permit and an inspection, and first-time or replacement gas appliances get inspected within 10 business days.

• Gas connections and venting: licensed work, always.
• Burners and gas valves: leave them alone.
• Relief valve: never cap it or plug it, even if it’s dripping. A drip is a reason to call a licensed plumber.

Homeowner exemptions aren’t something we could confirm, so ask WSSC Water plumbing inspections. See hiring a licensed plumber for what to ask. If water is pouring out, turn it off at the house valve.

What does a replacement look like?

Two links show the parts, so you can follow what a plumber quotes. They aren’t a suggestion to install anything yourself.

Questions on this page

Where each number comes from