What causes smelly water and what can be done about it?

There are many misconceptions regarding the development and treatment of water odors coming from a faucet or water heater.  The most common odor complaint “rotten egg smell” is derived from hydrogen sulfide gas dissolved in the water. Concentrations as little as 1 ppm, can result in this odor.

“Smelly water” is a non-toxic water condition and can be present in municipal water supplies with large reserves and low flow. Most often “smelly water” will be noticed with well water or when a water heater has not been used for a long period of time (vacations, etc.). This allows for the accumulation of this hydrogen sulfide gas creating or expanding an odor problem.  Active use of the water heater will reduce the problem.

How does an odor develop in a water heater?

1. A high concentration of sulfate in the raw water
2. Sulfate-reducing bacteria, non-toxic to humans (sulfate is reduced to a sulfide state by the bacteria)
3. Little or no dissolved oxygen in the water
4. Hydrogen (a component of water. More of a gasification of the hydrogen may be present due to water conditions reacting with the anode rod.)

With these factors, the hydrogen and sulfur combine to form the hydrogen sulfide gas that gives off the rotten egg, smelly, odor to the water.

Glass-lined water heaters feature at least one anode rod to protect the tank from corrosion. Smelly water can most easily be eliminated or reduced by replacing the anode(s) with one of less active material and then chlorinating the water heater tank and all hot water lines with a household bleach solution.

Anode Replacement reduces hydrogen ions, but does not eliminate the sulfate-reducing bacteria introduced into the water heater through the water supply. Therefore “smelly water” can still be present. Chlorination of your water heater may help for a short time or for water heaters where the “smelly water” condition only occurs when the water heater has not been in use for a long period of time. A long-term resolution may require chlorination of your well or water supply into the home. Contact your local water treatment professional for more information on chlorination of the water into your home.

Additional Information: Some water heaters are polymer lined. Polymer lined water heaters do not require an anode. In the case of “smelly water” (rotten egg odor) in a polymer lined heater, chlorination of your water heater may help if the condition is only present when the water heater has not been in use for a long period of time. The long-term solution most likely will require chlorination of your well or water supply into the home. Contact your local water treatment professional for more information on chlorination of the water into your home.