Frequent Questions

What are the health effects related to sulfur-reducing bacteria present in drinking water?

EPA does not have guidance or additional information related to the presence of sulfur-reducing bacteria in drinking water because sulfate is classified under the secondary maximum contaminant level (SMCL) standards based on taste, odor, color, corrosivity, foaming and staining properties of water. The SMCL for sulfate in drinking water is 250 milligrams per liter (mg/l), sometimes expressed as 250 parts per million (ppm). Sulfur-reducing bacteria and sulfur-oxidizing bacteria are related to water appearance problems and they pose no known health risks.

Sulfur-reducing bacteria are a group gram negative genera that are widespread and active in locations rich in sulfide and elemental sulfur made anaerobic by microbial digestion of organic materials producing hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners, and water heaters. These bacteria usually flourish on the hot water side of a water distribution system. Sulfate reduction can occur over a wide range of pH, pressure, temperature, and salinity conditions. Often sulfate and sulfur reduction is apparent from the smell of hydrogen sulfide (similar to rotten eggs) and the blackening of water and sediment by iron sulfide. Water with hydrogen sulfide alone (not sewage) does not cause disease; however, sulfate-reducing bacteria can negatively impact the water industry because of their primary role in the anaerobic corrosion of iron in pipelines, heating systems, and other structures.
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