Water Heater Smell Like Gas — Is It an Emergency or a Harmless Odor

Safety
By John F · · Updated March 7, 2026 · 7 min read

Quick Answer

If you smell rotten eggs or sulfur near your water heater, it’s usually NOT a gas leak; it’s hydrogen sulfide (H2S) from bacteria in your water heater or pipes. That’s harmless but annoying. However, if you smell odorless gas with mercaptan (sulfur added by utilities for safety), you have a real gas leak. The difference: rotten-egg smell = water problem; chemical-smell mercaptan = possible gas leak. When in doubt, leave your home, call Dominion Energy (1-800-333-4797) from outside, and let them check. Never stay inside if you suspect a gas leak. Your safety comes first…don’t assume it’s harmless.

Why This Is Dangerous (and When It’s Not)

Gas water heaters in Utah can produce three distinct smells:

1. Rotten egg / sulfur smell (hydrogen sulfide):

  • Smell: Unmistakable, like a dozen rotten eggs
  • Cause: Bacteria in your water heater or pipes producing hydrogen sulfide (H2S)
  • Danger level: LOW (bacteria aren’t dangerous to breathe; it’s just unpleasant)
  • Reality: This is WATER quality, not a gas leak
  • Location: Most common in basements (bacteria thrive in warm water)

2. Chemical / mercaptan smell (REAL GAS LEAK):

  • Smell: Sharp, unpleasant, distinctly chemical—not like rotten eggs
  • Cause: Natural gas with mercaptan added by utilities for leak detection
  • Danger level: HIGH (this IS a gas leak)
  • Reality: Requires immediate evacuation and professional inspection

3. Burning smell (slight, during first use):

  • Smell: Like burning dust or old paint
  • Cause: Dust on the burner or heat exchanger, normal when new or after long disuse
  • Danger level: LOW (usually dissipates after a few hours)
  • Reality: Not a gas leak, just combustion byproducts

The critical difference: Rotten-egg smell = harmless water issue. Chemical/mercaptan smell = real gas leak. When in doubt, evacuate.

Warning Signs to Distinguish a Gas Leak From H2S

Signs of hydrogen sulfide (rotten eggs—harmless):

  • Strong sulfur/rotten-egg smell only when hot water runs
  • Smell is concentrated near the heater or hot water pipes
  • You see no other problems (no hissing, no visible gas)
  • Others in your home smell it too (ruling out your imagination)
  • Smell has been present for weeks or months without issue

Signs of a REAL gas leak (call Dominion Energy immediately):

  • Distinct mercaptan (chemical) smell, not rotten-egg
  • Smell is strong and gets stronger over hours
  • Hissing or whooshing sound near the heater
  • All household members smell it
  • Smell is present even when water heater is off
  • You feel dizzy, nauseous, or have a headache
  • Pets are acting strange (lethargic, disoriented)

Safe Checks You Can Do Yourself

Step 1: Smell the difference.
Turn on a hot water tap and smell near the drain. Do you smell rotten eggs? That’s H2S—water issue. Do you smell something sharp and chemical? That’s different—possible gas leak.

Step 2: Check if it’s only hot water.
Turn on cold water and smell. Does the smell go away? If yes, the problem is in your hot water heater—likely H2S bacteria, not a gas leak.

Step 3: Check for visual signs of a leak.
Look at the base of the heater and around the gas line connections. Do you see bubbles in standing water (if there’s a leak)? Liquid dripping from the gas line? Visible corrosion? These suggest a real leak.

Step 4: Listen for hissing.
Is there a hissing sound? Gas leaks typically hiss or whoosh. Harmless H2S doesn’t make noise.

Step 5: Turn off the heater and wait one hour.
Does the smell dissipate? If yes, it’s water-related (H2S). If the smell remains strong with the heater off, it might be a gas line leak (call Dominion Energy).

When This Becomes Dangerous – Immediate Action Required

LEAVE YOUR HOME AND CALL DOMINION ENERGY (1-800-333-4797) IF:

  1. You smell a sharp, chemical smell (mercaptan) + hissing sound: This is a gas leak. Get out immediately. Don’t light anything. Call from outside.
  2. Everyone in your household is experiencing the same strong smell: Not your imagination. Evacuate. Call from a safe location.
  3. You feel lightheaded, dizzy, or nauseous while near the heater: These are signs of exposure to mercaptan or other gas compounds. Get fresh air immediately and call Dominion Energy.
  4. Your pets are acting lethargic or disoriented: Animals are sensitive to gas leaks. This is a red flag. Evacuate and call.
  5. The smell is present even when the water heater is completely off: Suggests a gas line leak separate from the heater. Evacuate and call.

DO NOT:

  • Light a match, lighter, or any flame to “test” the smell
  • Try to locate the leak yourself
  • Stay in the home while investigating
  • Close the door and hope it goes away

Dominion Energy will send a technician to inspect for FREE. It’s their job. Let them do it.

What a Technician Will Check and Do

If you call Dominion Energy or a plumber for a suspected gas leak:

  1. Pressure test the gas line with special equipment
  2. Use a soap-bubble test on all connections to detect leaks
  3. Check the heater’s burner and combustion area for issues
  4. Inspect the gas valve for corrosion or failure
  5. Test indoor air quality with a gas detector

If it’s a real leak: They’ll shut off the gas, isolate the leak, repair or replace the gas line, and pressure-test again before reopening.

If it’s hydrogen sulfide (rotten eggs): The gas company will confirm the heater is working correctly, then refer you to a plumber for H2S solutions (water softener, bacteria treatment, or heater replacement).

Typical Costs

Real gas leak repair:

  • Dominion Energy inspection: FREE
  • Gas line repair: $300–$800 (depending on location and severity)
  • Heater inspection/repair: $150–$500

Hydrogen sulfide (H2S) fix:

  • Water softener installation: $500–$2,000
  • In-heater treatment: $200–$400
  • Full heater replacement (if severe): $1,500–$2,500

Prevention: Stop Future Problems

1. For rotten-egg smells (H2S):

  • Install a whole-home water softener: $500–$2,000. This eliminates H2S bacteria by reducing minerals.
  • Replace your heater’s anode rod annually: $150–$250. Anode rods collect bacteria-feeding minerals.
  • Flush your heater semi-annually in Utah (hard water): $100–$200. Removes sediment where bacteria thrive (yikes!)

2. For gas leak prevention:

  • Have your gas line inspected annually by a licensed plumber: $100–$150
  • Check connections for corrosion monthly: FREE
  • Ensure proper venting (sealed combustion on newer units)

Find Local Help

A gas smell near your water heater might be harmless (H2S bacteria) or serious (gas leak). Don’t guess—call Dominion Energy for a free inspection if you suspect a leak. For harmless rotten-egg smells, a plumber can install water softening to eliminate the problem.

Frequently Asked Questions

Is it safe to use my water heater if it smells like rotten eggs?

Yes, if it’s the harmless rotten-egg smell (hydrogen sulfide). It’s unpleasant, not dangerous. You can use the water safely. It’s a water quality issue, not a gas safety issue.

Can I treat hydrogen sulfide without replacing my heater?

Yes. A whole-home water softener ($500–$2,000) eliminates the bacteria that produce H2S. Installing a softener is cheaper than a new heater and fixes the problem permanently.

Why does my heater suddenly smell like rotten eggs now?

Bacteria colonize the warm interior of your heater over time. It’s usually a sign the tank is aging and collecting sediment. Bacteria thrive in warm, mineral-rich water. Flushing (or softening) can slow it, but eventual replacement may be necessary.

What if I’m not sure if it’s a gas leak or H2S?

Always err on the side of caution. Call Dominion Energy (1-800-333-4797). They’ll confirm it’s safe for free. It’s better to be sure than to ignore a potential gas leak.

Is hydrogen sulfide from a water heater harmful to breathe?

Hydrogen sulfide in low concentrations (what your water heater produces) is harmless to breathe. It’s unpleasant and stinks, but it won’t poison you. High concentrations (industrial exposure) are dangerous, but your home won’t reach those levels.

Sources and Update Policy

This article was last updated March 2026. Information on gas safety and H2S treatment remains current.

Sources:

  • Enbridge gas safety: 1-800-333-4797
  • CDC hydrogen sulfide exposure guidelines
  • Environmental Protection Agency (EPA) water quality guidance on H2S bacteria
  • Utah water hardness: USGS, Wasatch Front 150–250 GPG
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