If your water smells like rotten eggs, that sulfur odor is hydrogen sulfide gas — and tracking down where it’s coming from is most of the battle. The single most useful clue is whether you smell it in the hot water, the cold water, or both. That one answer points you straight at the cause.
Start here: hot, cold, or both?
| Where you smell it | Most likely source |
|---|---|
| Hot water only | A reaction inside your water heater (the anode rod plus sulfate bacteria) — the most common case |
| Both hot and cold | The smell is in your water supply itself — common with well water or certain municipal sources |
| Only right when the tap turns on, then clears | Often not the water at all but gas from the drain. See why your house smells like sewer |
Why it’s usually the water heater
If only the hot water stinks, here’s what’s happening: every tank water heater has a magnesium anode rod that sacrifices itself to protect the steel tank from rust. In some water, that magnesium reacts with naturally occurring sulfate bacteria and produces hydrogen sulfide — the rotten-egg smell. It’s harmless to the tank, but unpleasant, and it gets worse when the heater sits unused (like after a vacation).
How to fix the hot-water smell
Two steps usually clear it:
- Flush and disinfect the tank. Draining and flushing the heater clears sediment the bacteria feed on; some homeowners follow with a controlled chlorine shock. While you’re at it, learn the full routine in my water heater guide, which covers tank access.
- Swap the anode rod. Replacing the standard magnesium rod with an aluminum/zinc or a powered anode usually stops the reaction for good while still protecting the tank. This is the real long-term fix.
If the heater is also old or struggling, it may be time to weigh repair against replacement — see my best water heater picks.
If the cold water smells too
When both hot and cold smell of sulfur, the issue is in your water source, not the heater. On well water this is common. The fix is treatment at the point of entry — depending on levels, a whole-house filter or a softener-plus-filter setup. My comparison of a water softener vs. a whole-house filter and my best water softener picks will help you pick the right one, and hard-water signs and fixes is worth a read since the two problems often travel together.
Is sulfur-smelling water safe?
At the low levels most homes see, hydrogen sulfide is a nuisance, not a health hazard — it tastes and smells bad and can corrode fixtures, but it isn’t typically dangerous to drink. Very high levels (rare, usually on private wells) warrant a water test. If you’re on a well and the smell is strong or sudden, testing the water is the smart move before you spend on treatment.
Frequently asked questions
Why does only my hot water smell like rotten eggs? The magnesium anode rod in your water heater is reacting with sulfate bacteria in the tank to produce hydrogen sulfide gas. Flushing the tank and switching to an aluminum/zinc or powered anode rod usually fixes it.
Is rotten-egg-smelling water safe to drink? At the low levels most homes have, it’s a nuisance rather than a health risk, though it tastes bad and can corrode fixtures. If you’re on a well and the smell is strong, have the water tested to be sure.
How do I get the sulfur smell out of my water heater? Drain and flush the tank to remove sediment, optionally disinfect it, and replace the standard magnesium anode rod with an aluminum/zinc or powered anode, which stops the reaction long term.
What if both hot and cold water smell? Then the sulfur is in your water supply, not the heater. It’s common with well water and is solved with whole-house treatment such as a filter or softener-plus-filter system.
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