Hydrogen Sulfide (Hydrogen Sulphide) is the chemical compound with the formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable and explosive. Dissolved in water, hydrogen sulfide is known as hydrosulfuric acid or sulfhydric acid, a weak acid.
Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body. Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs (pulmonary edema). Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness.

Hydrogen sulfide is a colorless gas that can exist naturally in groundwater. Methods to reduce or remove hydrogen sulfide include activated carbon filtration, shock chlorination, ion exchange, manganese greensand filtration, oxidation, oxidizing filtration, ozone treatment, and water heater modification.