Rotten Egg Odor

If you notice this smell in your water, it probably contains hydrogen sulfide (H2S) gas. Sources of this gas include:

• Decay of organic matter or chemical reactions with sulfur-containing minerals in soil and rock.
• Sulfate-reducing bacteria which convert naturally occurring sulfate and other sulfur compounds to hydrogen sulfide gas.
• Water heaters can produce hydrogen sulfide gas by:
  • Providing a warm environment for sulfate-reducing bacteria to live.
  • The anode, which is usually magnesium, supplies electrons that sustain the reaction of sulfate to hydrogen sulfide gas.
    

Should hydrogen sulfide gas or sulfur-reducing bacteria concern me?

In addition to the hydrogen sulfide gas they produce, sulfur-reducing bacteria also generate slime that can promote the growth of other bacteria and clog wells and plumbing.

Hydrogen sulfide gas may cause black staining of silverware and plumbing fixtures and can corrode pipes.

How do I determine the source?

Run water separately from both the cold and hot taps, preferably when you have been away from the house for a few hours so your sense of smell is more keen.

• If the smell is only from the hot water tap, the source is most likely your water heater.
• If the smell is from both hot and cold taps, but only from water treated by a water softener, you may have sulfur-reducing bacteria in your water softener.
• If the smell is from both taps and diminishes after the water runs, you may have sulfur-reducing bacteria in your well or piping.
• If the smell is from both taps and is persistent, you may have hydrogen sulfide gas in your groundwater.
  

How can I eliminate hydrogen sulfide gas?

• If the source is your water heater:
  • Remove or replace the magnesium anode.
  • Disinfect and flush the water heater with a bleach solution.
  • Increase the water temperature to 160 degrees Fahrenheit for several hours to kill the bacteria, then flush the heater.
    If you are not very familiar with water heater operation and maintenance, contact a plumber or water heater dealer to perform the service.
• If the source is sulfur-reducing bacteria in the well or plumbing:
  • Disinfect the well. (See section on Well Disinfection)
• If the source is sulfur-reducing bacteria in a water softener or treatment unit:
  • Contact the manufacturer for instructions on disinfecting the unit.
• If the source is hydrogen sulfide gas in the groundwater the water may be treated by:
  • Activated carbon filters for hydrogen sulfide concentrations less than 1 mg/L.
  • Manganese greensand filters for hydrogen sulfide concentrations up to 6 mg/L.
  • Oxidation filtration systems for hydrogen sulfide concentrations up to and exceeding 6 mg/L.

Source: Minnesota Department of Health, Division of Environmental Health, Hydrogen Sulfide and Sulfur Bacteria in Well Water.