Hydrogen Sulphide/ Rotten Egg Smell RemovalRotten Egg Smell Chlorine Filters The smell of rotten eggs in water is caused by hydrogen sulfide gas (H2S). This gas is produced by several things, including: Sulfur reducing bacteria: These bacteria are commonly found in wells and plumbing systems. They break down organic matter that contains sulfur, releasing H2S gas in the process . Natural decomposition: When organic matter (like leaves or plants) decomposes in water, it can release H2S gas