If you notice a smell similar to rotten eggs (sulfur) or sewage when running water, it might be caused by gases residing in the sink drain. In the drain, bacteria live on food, soap, hair, etc. When water goes down a drain, these gases are released into the air. These odors are often mistakenly associated with the water because they are observed only when the water is running. In this case, the odor is not in the water, it is merely the water pushing the gas out of the drain. To resolve the drain odor, we recommend that you clean the drain.