Sulfides are naturally present in ground waters as a result of leaching from sulfur-containing mineral deposits. Surface waters do not usually contain high sulfide concentrations. Hydrogen sulfide, the most common form of sulfide, has limited industrial applications and is present primarily as a by-product of various industrial or natural processes. It is highly corrosive to both metal and concrete surfaces.

Hydrogen sulfide fumes are noxious and highly toxic. When escaping from a water supply, their odor can be detected in concentrations as low as 0.25 µg/L. Sulfides result from the decomposition of organic matter, from bacteria which can reduce sulfate under anaerobic conditions, and as a by-product in various processes including petroleum refining.

The Colorimetric Method. CHEMetrics' test kits measure total acid soluble sulfides and employ methylene blue methodology. Sulfides react with dimethyl-p-phenylenediamine in the presence of ferric chloride to produce methylene blue. Results are expressed as ppm (mg/L) S.