Hot water from the faucet smells like rotten eggs

Symptoms

• Sulfur or rotten-egg smell in hot water only
• Cold water at the same faucet has no odor
• Smell is stronger after the water hasn't been used for a while
• No gas smell present anywhere in the home

Likely causes

• CommonBacteria reacting with the water heater's anode rodSulfate-reducing bacteria in the tank produce hydrogen sulfide gas, which smells like rotten eggs.
• PossibleSulfur naturally present in the water supplyMore common with well water than municipal water.
• PossibleAging anode rod needing replacementA degraded rod can make the reaction more pronounced.
• Less commonStagnant water in a rarely used lineRarely used hot lines can develop odor from standing water.

What to do

1. Confirm the smell is only in hot water and not a gas smell, which is a different, urgent issue.
2. Run the hot water for a few minutes to see if fresh water from the tank clears the smell temporarily.
3. If it returns after standing, the water heater's anode rod is the most likely cause.
4. Consider having the anode rod flushed or replaced, which a plumber can do, or ask about a different rod material (like aluminum/zinc) that reduces the reaction.
5. As a temporary measure, some people find flushing and chlorinating the tank helps, though this is best guided by a plumber's instructions.
6. If the smell is present in cold water too or seems like a gas odor, treat it as a safety issue instead of an anode rod issue.

Tools and parts

When to call a pro

If you smell gas anywhere in the home rather than just rotten eggs in hot water, leave the house and call the gas utility or 911 rather than investigating the faucet.

Safety