Quick answer
If only the hot water smells like rotten eggs, the cause is almost always in the water heater: sulfate-reducing bacteria in the tank react with the magnesium anode rod and produce hydrogen sulfide gas. It is most common with well water and heaters that sit unused. Flushing the tank and disinfecting it helps for a while; replacing the magnesium anode with an aluminum-zinc anode usually fixes it. If cold water smells too, the source is the water supply, not the heater. Call (888) 217-6781 to reach a plumbing company taking calls in your ZIP.
Follow the short menu, then your 5-digit ZIP. The line goes quiet for a few seconds while it connects; stay on. If it does not connect, call once more: companies taking calls change minute to minute.
Written & reviewed by Marcus ReedIICRC WRT
Reviewed November 4, 2026· Next review May 2027
A sulfur or rotten egg smell when you turn on the hot tap, but not the cold, is a well-known water heater problem. It is unpleasant, but usually fixable.
Confirm Where It Comes From
| What smells | Where the problem is |
|---|---|
| Hot water only | The water heater |
| Hot and cold water | The water supply; well water often |
| One drain, not the water | The drain trap; see drain smells like rotten eggs |
| Near a gas appliance, in the air | Possible gas leak: leave and call the gas utility |
Why It Happens
Most tank heaters have a magnesium anode rod that corrodes so the tank does not. Sulfate-reducing bacteria, common in well water, react with it and produce hydrogen sulfide, the rotten egg gas. It is worse when the heater sits unused, or the thermostat is set low.
Talk to a plumber about this
One call reaches a plumbing company taking calls in your ZIP.
How It Is Fixed
- 1Flush the tank through the drain valve to remove sediment where bacteria live. See water heater maintenance.
- 2Disinfect the tank if the manufacturer's instructions allow it; this is a temporary fix.
- 3Replace the anode with an aluminum-zinc anode, which reacts far less. This is the usual lasting fix. Do not remove the anode without replacing it.
- 4Test the water if cold water smells too. CDC guidance on private wells covers hydrogen sulfide and testing.
What It Costs
An anode swap is a common, short plumbing job; see water heater repair for typical prices.
The Call
Call when flushing does not clear it, or the anode is seized in the tank. (888) 217-6781 connects you to a plumbing company taking calls in your ZIP. Follow the short menu, enter your 5-digit ZIP and stay on while it connects; if it does not connect, call once more, because the companies taking calls change minute to minute.
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Frequently Asked Questions
Why does my hot water smell like rotten eggs?
Bacteria in the tank react with the magnesium anode rod and produce hydrogen sulfide. It is common with well water and in heaters that sit unused.
Is rotten egg smell in hot water dangerous?
At the low levels that cause a smell in tap water it is usually a nuisance, not a hazard. A rotten egg smell near a gas appliance, though, can be a gas leak: leave and call the gas utility.
Should I remove the anode rod to stop the smell?
NoWithout an anode the tank corrodes quickly and the warranty may be void. Replace it with an aluminum-zinc anode instead.
Sources
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Disclaimer: HearthDry is an independent educational resource. This article is for informational purposes only and does not constitute professional, legal, or insurance advice. Consult licensed professionals before making decisions about your property or insurance claims.
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