Hot water smells like rotten eggs

Symptoms

• Hot water has a sulfur or rotten-egg smell
• Cold water smells normal
• Smell may be stronger after the tank sits unused for a while
• Household uses well water (more common there)

Likely causes

• CommonBacteria reacting with the magnesium anode rodSulfate-reducing bacteria naturally present in some water supplies react with the anode rod to produce hydrogen sulfide gas, which smells like rotten eggs.
• CommonWell water with naturally occurring sulfur bacteriaThis is especially common in homes on well water rather than municipal supply.
• PossibleAnode rod nearing the end of its life and reacting more activelyA heavily corroded rod can sometimes worsen the smell before it's fully consumed.

What to do

1. Confirm the smell is specific to hot water and not present in cold water from the same tap.
2. Flush the tank thoroughly (see the sediment flushing guide) to remove water that may be harboring bacteria.
3. Consider having the anode rod inspected and replaced with a different type, such as a zinc-aluminum or powered anode rod, which reduces the reaction with sulfur bacteria.
4. If on well water, ask about shock-chlorinating the well and plumbing system, which can eliminate the bacteria at the source.
5. Raise the tank temperature briefly to around 140°F for a few hours, which can kill some bacteria, then lower it back to a safe setting.
6. If the smell returns quickly after these steps, a plumber experienced with well water systems can recommend a longer-term fix.

Tools and parts

• Garden hose (for flushing)

When to call a pro

If flushing and an anode rod swap don't resolve it, especially on well water, a plumber or water treatment specialist can test for and treat the underlying bacteria.

Safety