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Water heater · triage

Hot water smells like rotten eggs

The short answer

First rule out gas: if the smell is in the air near the heater or stove rather than in the water, use the gas card. If only the hot water smells, it is usually hydrogen sulfide from bacteria reacting with the tank’s anode rod.

Air or water?Natural gas is odorized to smell like rotten eggs. A smell in the air near gas appliances means leave and call; a smell only when hot water runs is a water-quality issue.

Know your shutoffs

Gas shutoffAt the gas meter outside (a valve on the pipe before the meter), and a smaller shutoff valve on the gas line next to each appliance.

Every outcome on this card

Emergency nowIt may be a gas leak

Leave and call from outside.

  1. Get everyone out
  2. Don't make a spark No switches, phones or lighters inside.
  3. Call the gas utility or 911 from outside
This monthSmelly hot water

A nuisance, not a hazard at tap levels. Fix it this month.

  1. Run cold water to confirm it does not smell
  2. Ask a plumber about the anode rod Swapping a magnesium rod for an aluminum-zinc or powered anode is a common fix.
  3. Ask about a disinfecting flush of the tank Follow the manufacturer’s instructions; it is plumber work if you are unsure.

Sulfate-reducing bacteria in a warm tank react with the anode rod and make hydrogen sulfide, the rotten-egg smell.

This monthWell water with a sulfur smell

Test the water, then fix the heater.

  1. Have your well water tested Your county or state health department lists certified labs.
  2. Ask a plumber or water-treatment pro about the anode and treatment
  3. Log the results

Wells can carry sulfur bacteria or dissolved hydrogen sulfide; the heater makes it worse.

This weekAll the water smells

Call your water utility this week (or test a well).

  1. Note when it started and which taps
  2. Call your water utility They track odor reports.
  3. If you have a well, have it tested

Related

You smell gasSewer or rotten-egg smell in the house

Written from

Original casaq guidance, updated 2026-10-05. General guidance, not a diagnosis; licensed-pro review pending. Severity levels: Emergency now / Today / This week / This month / Watch. Send a correction.

Step 1

Where is the smell?