Sometimes customers report that their tap water smells septic, swampy, moldy or like sewage or sewer gas, or sometimes sulfur or rotten eggs. These odors are often caused by gases forming in the household drain. These gases are formed by bacteria which 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.
If you determine it is the drain, you can eliminate this type odor by disinfecting the drain to kill the bacteria. Effective disinfection can be achieved by following these six steps.
Caution: do not mix any drain cleaners or detergents with bleach; certain combinations can create toxic fumes
- Run the cold water for about 15 seconds into the drain that is to be disinfected, then turn the water off.
- Pour approximately quarter cup of liquid chlorine bleach (laundry bleach) down the drain (or drains) where the odor is present. Pour the bleach slowly around the edges of the drain so that it runs down the sides of the drain. Caution: bleach may cause eye damage, skin irritation, and may damage clothing - BE CAREFUL!
- If the odor is coming from a sink with a garbage disposal, turn the disposal on for a few seconds while the bleach is being poured. This will disperse the bleach around the inside of the disposal. Caution: bleach may cause eye damage, skin irritation, and may damage clothing - take care to avoid splashing for the few seconds the disposal is turned on.
- Allow the bleach to remain undisturbed in the drain for about 10 minutes. Caution: prolonged contact with metals may cause pitting and/or discoloration.
- After 10 minutes, run the hot water into the drain for a minute or two to flush out the bleach. If a garbage disposal was disinfected, thoroughly flush it as well.
- This procedure may need to be repeated if the odor returns.
If the odor is detected only in your hot water supply, it may be an indication that there is an issue with your hot water heater. A sulfurous or rotten egg-like odor in the hot water is caused by bacteria growing in the water heater. This usually happens when the water heater is turned off while on vacation, when the hot water has not been used for a long time, or when the temperature setting on the heater is set too low. You should consult your owner's manual or contact a licensed plumber to address this issue.