Water containing objectionable amounts of hydrogen sulfide gas which causes an offensive “rotten egg” odor. Sulfur is found in two forms: gaseous and dissolved. For complete odor removal, both must be considered. Amounts of hydrogen sulfide in water can fluctuate greatly. High levels of hydrogen sulfide gases are hazardous to health and can cause blindness. Exposure to sulfide gas in excess of 50 ppm is known to be fatal.