How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Why does the water have a rotten-egg smell in some empty houses?
Thursday, October 11, 2018
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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