Rotten Eggs (Sulfurous), Decayed or Sewage-like Odor
Generally, a rotten egg (or sulfurous), decayed or sewage-like odor in household water is a result of bacterial activity, which can be due to:
Bacteria growing in the drain: This is the most common cause of these types of odors. Over time, organic matter such as hair, soap and food waste can accumulate on the walls of the drain. These deposits serve as a food for bacteria to grow. The bacteria can produce a gas that smells like rotten eggs or sewage. Address this problem by following these two steps:
First, ensure that both the cold and hot water have the smell and that the smell is coming out of one or several faucets, but not all. Fill a glass with water from the sink that has the smell, then step away from the sink and swirl the water around inside the glass few times. If the problem is in the drain, the tap water in the glass should not have an odor.
If the water in the glass does not smell, you should disinfect and flush the drain.
Bacteria growing in the water heater: Bacteria growing in the water heater can also produce a rotten egg or sewage smell. Frequently, this occurs if the hot water is unused, if the water heater is turned off for a significant period of time or if the thermostat on the heater is set too low. Generally, the bacteria that produce this problem are not a health threat; however, the taste and odor can be very unpleasant. To address this problem, the following actions are suggested:
Make sure that hot water smells, but cold water does not. Often, the smell originates from a magnesium heating rod in the hot water tank.
If the heater has a magnesium rod, a licensed plumber can replace it with an acceptable alternative such as an aluminum rod.