First: is it the water or the air?
Natural gas has a sulfur-like odorant added so leaks can be noticed. If the smell is in the room even with no water running, especially near the water heater, furnace or stove, leave the house and call your gas utility from outside. See what to do if you smell gas.
If the smell appears only when water runs, and mostly from hot taps, it's in the water.
Narrowing it down
- If Only hot water smells
- Water heater: bacteria and the anode rod. Most common on private wells and some groundwater supplies.
- If Hot and cold both smell
- Hydrogen sulfide in the water supply itself, common with wells. Treatment happens before the heater, such as aeration or oxidizing filtration. See water filtration.
- If Only one sink smells
- Probably the drain, not the water. Bacteria in the trap or overflow. See sewer smell in the house.
Fixes that work
Replace the anode rod
Most commonTell: Magnesium anodes feed the reaction that makes the smell.
Fix: An aluminum-zinc anode or a powered anode, which doesn't react the same way.
Disinfect the tank
PossibleTell: Bacteria persist after the anode change.
Fix: A plumber can shock-chlorinate the tank and flush it.
Treat the supply
PossibleTell: Cold water smells too.
Fix: Whole-house treatment matched to a water test.
Why it happens in some homes and not others
The bacteria involved thrive where water carries sulfate and the heater sits unused or at a low temperature, such as a vacation home, a heater turned down to save energy, or a house on well water. A water softener can make the reaction more likely because softened water lets the magnesium anode react faster. That's why the smell often appears after a softener is installed or a house sits empty for a few weeks, and why the anode is the part to change rather than the softener.
When to involve a plumber
- Removing an anode often takes a large socket and a lot of torque, and old tanks can be damaged doing it.
- Any time the anode is removed, the tank should be checked for heavy corrosion.
- If you're on a well, a water test first avoids buying the wrong treatment.
More questions
Is rotten-egg smelling water safe?
Hydrogen sulfide at the levels that cause odor is usually a nuisance rather than a health hazard, but a well that suddenly develops a smell should be tested.
Can I just remove the anode rod?
Removing it without replacement stops the smell but leaves the steel tank unprotected, and it will corrode much faster. It also can void the warranty.