Water FAQs

What Causes the Rotten Egg Smell in my Well Water? Is it Harmful?

The rotten egg (sulfur) smell in your well water is technically called Hydrogen Sulfide Gas (H2S). Hydrogen sulfide gas can result from a number of different sources.

  • It can occur naturally in groundwater.
  • It can be produced by “sulfur bacteria” in the groundwater, in the well, or in the water distribution system.
  • It can be produced also by sulfur bacteria or chemical reactions inside water heaters.
  • In rare instances, it can result from pollution.
  • The source of the gas is important when considering treatment options.

Are sulfur bacteria or hydrogen sulfide harmful?

In most cases, the rotten egg smell does not relate to the sanitary quality of the water. However, in rare instances the gas may result from sewage or other pollution. It is a good idea to have the well tested for the standard sanitary tests of coliform bacteria and nitrate.

Sulfur bacteria are not harmful, but hydrogen sulfide gas in the air can be hazardous at high levels.

Are there other problems associated with sulfur bacteria or hydrogen sulfide?

Yes. Sulfur bacteria produce a slime and can promote the growth of other bacteria, such as iron bacteria. The slime can clog wells, plumbing, and irrigation systems. Bacterial slime may be white, grey, black, or reddish brown if associated with iron bacteria. Hydrogen sulfide gas in water can cause black stains on silverware and plumbing fixtures. It can also corrode pipes and other metal components of the water distribution system.

What causes hydrogen sulfide gas to form in groundwater?

Decay of organic matter such as vegetation, or chemical reactions with some sulfur-containing minerals in the soil and rock, may naturally create hydrogen sulfide gas in groundwater. As groundwater moves through soil and rock formations containing minerals of sulfate, some of these minerals dissolve in the water. A unique group of bacteria, called “sulfur bacteria” or “sulfate-reducing bacteria” can change sulfate and other sulfur containing compounds, including natural organic materials, to hydrogen sulfide gas.

How is hydrogen sulfide gas produced in a water heater?

A water heater can provide an ideal environment for the conversion of sulfate to hydrogen sulfide gas. The water heater can produce hydrogen sulfide gas in two ways – creating a warm environment where sulfur bacteria can live, and sustaining a reaction between sulfate in the water and the water heater anode. A water heater usually contains a metal rod called an “anode,” which is installed to reduce corrosion of the water heater tank. The anode is usually made of magnesium metal, which can supply electrons that aid in the conversion of sulfate to hydrogen sulfide gas. The anode is 1/2 to 3/4 inches in diameter and 30 to 40 inches long. It should be removed as long as you soften the water first.

How can I find the source of a hydrogen sulfide problem, and what can I do to eliminate it?

The odor of hydrogen sulfide gas can be detected in water at a very low level. ( .02 ppm)Smell the water coming out of the hot and cold water faucets. Determine which faucets have the odor. The “rotten egg” smell will often be more noticeable from the hot water because more of the gas is vaporized. Your sense of smell becomes dulled quickly, so the best time to check is after you have been away from your home for a few hours. If the smell is only from the hot water faucet the problem is likely to be in the water heater. If the smell is in both the hot and cold faucets then the problem is likely caused from hydrogen sulfide or sulfur bacteria in the well.

What if the smell is just in my hot water?

(Unless you are very familiar with the operation and maintenance of the water heater, you should contact a water system professional, such as a plumber, to do any work on your water heater.)

If the smell is just coming from your hot water, and not at all from your cold water, then replacing or removing the magnesium anode rod in your hot water tank may be the solution. Many water heaters have a magnesium anode, which is attached to a plug located on top of the water heater. It can be removed by turning off the water, releasing the pressure from the water heater, and unscrewing the plug. Be sure to plug the hole. However The anode rods pupose is to provide corrosion protection, you will have to install a water softener,if you have a water softener or already have soft water the anode rod is not needed. Disinfect and flush the water heater with a chlorine bleach solution: Chlorination can kill sulfur bacteria, if done properly. If all bacteria are not destroyed by chlorination, the problem may return within a few weeks. Kill the bacteria with heat: Increase the water heater temperature to 160 degrees Fahrenheit (71 degrees Celsius) for several hours. This will destroy the sulfur bacteria. Flushing to remove the dead bacteria after treatment should control the odor problem.