The smell happens when you turn on a hot water faucet after the hot water heater has been sitting unused for a while. It doesn’t matter whether it has been on or off. Anaerobic bacteria, which  exist in many water systems, cause the stinky smell when they react with the sacrificial anodes, which are long magnesium or aluminum rods that protrude into the steel water heater tank to protect it from corrosion. The reaction creates hydrogen sulfide gas--the classic rotten-egg odor.

   The smell is barely noticeable when the water flows regularly through the tank while the home is occupied, but builds up if it is unused for an extended period of time. You can open a hot water faucet and let it run for a while to make it dissipate.

   Sacrificial anodes are the unsung heroes of long water heater life. Essentially, they corrode--sacrificing their metal--to avoid corrosion of the steel tank material during the unavoidable electrolytic reactions in a water tank. To learn more about them, see our blog post Why do water heaters have a sacrificial anode? 

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Here’s links to a collection of our other blog posts about PLUMBING:

• How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

• Why is there sand in the bottom of my toilet tank?  

• What causes a gurgling sound when a bathtub or sink drains? 

• Are drop-in toilet bowl cleaner tablets safe? 

• What can I add to my septic tank to help it work better?

• What are the code requirements for layout of drain piping under sinks? 

• Why is there mold inside my toilet tank?  

• What are the pros and cons of a wall-mounted toilet?

• Which plumbing fixtures require water shut off valves in a home? 

• How can I tell if a house is connected to a septic tank system or sewer?

• Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water? 

• Why is a backflow preventer required on lawn sprinkler systems? 

• How can I locate my septic tank? 

• Is a hot water faucet handle required to be on the left? 

• Can you live in a house while the plumbing is being replaced? 

• Why is the European-style bottle trap not approved by the plumbing codes in the U.S.? 

• Why can't PVC be used for water pipe inside a house? 

• What are the common problems to look for when the plumbing has been replaced in a house? 

• What's that powdery crust on the pipe connections at the water heater? 

• How can I tell what type of plumbing pipe I have? 

  • What causes low water pressure in a house?

• Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

• How do I get rid of the sewer gas smell in my house?  

    Visit our WATER HEATERS and PLUMBING pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.