Manganese forms brownish-black particles in water that can stain plumbing fixtures, fabrics, dishes and utensils when it combines with oxygen in water. Manganese can produce a black color in water and also give a noticeable bitter, metallic taste to water, food, and beverages such as tea and coffee (Manual of Small Public Water Supply Systems; EPA570-9-91-003; May 1991). Manganese is an essential nutrient and it has been estimated that the daily intake from a normal diet is about 10 mg. Ingestion of manganese in moderate excess of the normal dietary level is not considered harmful (National Secondary Drinking Water Regulations; EPA570-9-76-000; June 1984). EPA set a non-enforceable secondary maximum contaminant level of 0.05 mg/L for manganese in order to prevent most aesthetic effects.
Hydrogen sulfide gas in association with iron can cause black stains on plumbing fixtures. In addition, the presence of dissolved hydrogen sulfide gas may tarnish silverware and cause a "rotten egg" odor in water. EPA has not set a standard for hydrogen sulfide in drinking water.
Very high chloride content in tap water causes blackening and pitting of stainless steel sinks. High chloride ion concentration can also produce a salty taste in tap water and result in corrosion of piping. EPA has set a non-enforceable secondary maximum contaminant level of 250 mg/L for chloride to prevent most aesthetic effects.
To help determine the cause(s) of aesthetic or cosmetic effects from your drinking water, contact your local drinking water system. Additional guidance for household well owners is available at http://www.epa.gov/privatewells. General information on nuisance chemicals is available at http://www.epa.gov/dwstandardsregulations/secondary-drinking-water-standards-guidance-nuisance-chemical .