Water Heater Smell Like Gas — Is It an Emergency or a Harmless Odor
Quick Answer
If you smell rotten eggs or sulfur in the air near your water heater or gas line, treat it as a possible gas leak. Utilities add mercaptan to natural gas so that a leak smells like rotten eggs. Leave your home first, then call Enbridge’s gas emergency line (1-800-767-1689) or 911 from outside. A sulfur smell that comes only from your hot water at the tap is more often hydrogen sulfide (H2S) from bacteria in the water heater, which is a water-quality problem. If you can’t tell which one you have, assume it’s gas. Never stay inside if you suspect a gas leak.
Why This Is Dangerous (and When It’s Not)
Gas water heaters in Utah can produce three distinct smells:
1. Rotten-egg smell in your hot water only (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: A water-quality problem, but only if the smell comes from the water itself. A rotten-egg smell in the air is #2.
Location: Most common in basements (bacteria thrive in warm water)
2. Rotten-egg or sulfur smell in the air near the heater or gas line (POSSIBLE GAS LEAK):
Smell: Rotten eggs or sulfur. Natural gas has no smell of its own; the mercaptan utilities add makes a leak smell this way.
Cause: Natural gas with mercaptan added by utilities for leak detection
Danger level: HIGH (treat it as a gas leak until Enbridge says otherwise)
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: where the smell is. Rotten eggs only in the hot water at the tap usually means H2S. Rotten eggs or sulfur in the air near the heater, the gas line or anywhere in the house means a possible gas leak. When in doubt, evacuate.
Warning Signs to Distinguish a Gas Leak From H2S
Signs of hydrogen sulfide (a water-quality problem):
Strong sulfur/rotten-egg smell only when hot water runs
The smell is in the water itself, not in the air around the heater
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 Enbridge immediately):
Rotten-egg or sulfur smell in the air, not just in your hot water
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.
Only do these checks if the smell is faint and comes from your water. If the air near the heater or gas line smells like rotten eggs, skip them: leave and call 1-800-767-1689 from outside. Otherwise, run a hot water tap and smell the water. A rotten-egg smell from the water itself points to H2S.
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. H2S in the water 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 Enbridge).
When This Becomes Dangerous – Immediate Action Required
LEAVE YOUR HOME AND CALL ENBRIDGE GAS (1-800-767-1689) IF:
You smell rotten eggs or sulfur in the air, or hear hissing near the heater or gas line: This may be a gas leak. Get out immediately. Don’t light anything. Call from outside.
Everyone in your household is experiencing the same strong smell: Not your imagination. Evacuate. Call from a safe location.
You feel lightheaded, dizzy, or nauseous while near the heater: These can be signs of a gas problem. Get fresh air immediately and call Enbridge.
Your pets are acting lethargic or disoriented: Animals are sensitive to gas leaks. This is a red flag. Evacuate and call.
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
Enbridge’s gas emergency line is staffed 24/7. Call them and let them check it.
What a Technician Will Check and Do
If you call Enbridge or a plumber for a suspected gas leak:
Pressure test the gas line with special equipment
Use a soap-bubble test on all connections to detect leaks
Check the heater’s burner and combustion area for issues
Inspect the gas valve for corrosion or failure
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 in the hot water): That’s a plumbing job, not a gas one. A plumber can replace the magnesium anode rod with an aluminum one or disinfect the tank with a chlorine flush.
Typical Costs
Real gas leak repair:
Gas line repair: $300–$800 (depending on location and severity)
Heater inspection/repair: $150–$500
Hydrogen sulfide (H2S) fix:
Anode rod swap (magnesium to aluminum): $150–$250
In-heater treatment: $200–$400
Full heater replacement (if severe): $1,500–$2,500
Prevention: Stop Future Problems
1. For rotten-egg smells (H2S):
Replace the magnesium anode rod with an aluminum one: $150–$250. Magnesium can react with sulfate in the water to make hydrogen sulfide. Aluminum still protects the tank from corrosion without that reaction.
If the smell comes back, have a plumber disinfect and flush the tank with a chlorine bleach solution. Heating the tank to 160°F for a few hours also kills sulfur bacteria, but that’s a scald risk, so leave it to a pro and turn the thermostat back down afterward.
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 rotten-egg smell near your water heater can be a gas leak or, if it comes only from your hot water, hydrogen sulfide. Don’t guess: if you suspect a leak, leave and call Enbridge from outside. For a sulfur smell in your hot water, a plumber can treat the problem.
Enbridge gas emergency: 1-800-767-1689
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Frequently Asked Questions
Is it safe to use my water heater if it smells like rotten eggs?
If the smell comes only from your hot water, it’s usually hydrogen sulfide: unpleasant, and a water-quality problem rather than a gas safety one. If you smell rotten eggs in the air near the heater or gas line, don’t use anything. Leave and call Enbridge (1-800-767-1689) or 911 from outside.
Can I treat hydrogen sulfide without replacing my heater?
Yes. The usual fix is swapping the magnesium anode rod for an aluminum one, sometimes with a chlorine flush of the tank. A water softener won’t fix it. In rare cases a softener can even give sulfur bacteria a place to grow.
Why does my heater suddenly smell like rotten eggs now?
Sulfur bacteria can settle in the warm tank, and the magnesium anode rod can turn sulfate in your water into hydrogen sulfide. An aluminum anode or a chlorine flush usually takes care of it without replacing the heater.
What if I’m not sure if it’s a gas leak or H2S?
Treat it as a gas leak. Leave the house and call Enbridge (1-800-767-1689) from outside. Their emergency line is staffed 24/7.
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 October 2026. Gas safety and H2S treatment advice was checked against Enbridge Gas Utah and state health sources.
Sources:
Enbridge Gas Utah: Smell natural gas? Emergency line 1-800-767-1689
Minnesota Department of Health: Hydrogen sulfide and sulfur bacteria (water heater anode, chlorine flush, high-temperature treatment)
Penn State Extension: Hydrogen sulfide (rotten egg odor) in water wells (magnesium anode, water softeners)
CDC hydrogen sulfide exposure guidelines
Environmental Protection Agency (EPA) water quality guidance on H2S bacteria
Utah water hardness: USGS, Wasatch Front 14–22 GPG