Why does my water smell like rotten eggs or sewage?

Sometimes customers report that their tap water smells septic, swampy, moldy, or like sewage, sewer gas, sulfur, or rotten eggs. These odors are often caused by gases forming in the household drain. These gases are formed by bacteria that live on food, soap, hair, and other organic matter in the drain. These gases are heavier than air and remain in the drain until the water is turned on. As the water runs down the drain, the gases are expelled into the atmosphere around the sink. It is natural to associate these odors with the water because they are observed only when the water is turned on. In this case, the odor is not in the water, it is simply the water pushing the gas out of the drain. This can be verified by taking a glass of water from the tap and walking away to another area to smell the glass of water.

Cold Water: If the odor is not evident in the glass, but is noticeable when you are standing at the sink with the cold water is running, then the odor is most likely coming from the drain. This problem is easily solved by filling the sink with hot water, adding a few ounces of chlorine bleach, and allowing the hot chlorinated water to flush and disinfect the drain. It is also good practice to periodically remove and clean the sink stopper. The garbage disposal in the kitchen sink can be cleaned in a similar manner.

Hot Water: If you find these odors in your hot water, there are 2 probable causes:

  • Bacteria may be residing in the water heater. Disinfecting the water heater may eliminate this odor. Heat disinfection is used to eliminate the bacteria. If you do not feel comfortable doing this work yourself, hire a licensed plumber to do it for you.
  • The water heater anode may need to be replaced. If experienced, inspect the anode yourself; otherwise, call a plumber.