Sulfates are a combination of sulfur and oxygen, which are both naturally occurring and man-made. Sulfates are commonly found in various soil sediments and rock formations. Over time, these minerals dissolve and are released into the ground water. Sulfates enter the ground water from a wide variety of industrial processes as well, from tanneries to steel mills to textile plants. Sulfates are used as pickle liquor for steel and metal industries, as feedstock or reagent in various manufacturing processes, and as fungicides and algicides (frequently in the form of copper sulfate). Acid rain is created when sulfur oxides produced during combustion of fossil fuels are transformed into sulfuric acid in the atmosphere. Household detergents also contribute to sulfate contamination.

When sulfates are present in drinking water they may cause the water to have a bitter taste, and may have a laxative effect that can lead to dehydration. These effects appear to be temporary, however, and seem to be limited to those people not accustomed to ingesting sulfate in drinking water, such as newborns, visitors, and new residents.

Do the Sulfate Provisions Apply to Your Community?

Since sulfates do not appear to pose any significant health hazards, EPA has not yet established National Primary Drinking Water Standards for sulfates. A Maximum Contaminant Level (MCL) of 500 mg/l was proposed for sulfates on December 20, 1994, but was abandoned by the Safe Drinking Water Act Amendments of 1996 (SDWAA). Instead, the SDWAA requires EPA and the Centers for Disease Control (CDC) to conduct a definitive study on the health risks of sulfate before any final regulations are promulgated. Should EPA adopt MCLs for sulfate, however, it will be your community's responsibility to maintain sulfate levels in your drinking water system at or below the established level.

Currently, the only regulation in place limiting sulfate levels in drinking water is a secondary standard of 250 mg/l. This standard was adopted to control the foul odor present in sulfate-laden water. Secondary standards, however, are not federally enforceable -- they are merely recommendations, and it is up to your state and/or community to decide whether or not to abide by them.

Actions Your Community Should Be Taking

Since there is no federally enforceable standard currently in place for sulfates, you need not be concerned with the sulfate levels in your drinking water unless your state has adopted the secondary drinking water standards. You should, however, take steps to reduce the odor caused by sulfate in your drinking water system if you find that this is a problem.

Small quantities of water can be treated for sulfate contamination through the use of either distillation (boiling the water and sifting out the sulfates and other minerals) or reverse osmosis. Large quantities of drinking water are often treated for sulfate contamination with ion exchange, a process similar to water softening in which sulfates are adsorbed by ion-exchange resin.

You would be well advised to keep an eye on the progress of the development of regulatory standards for sulfate, in order to be prepared should new primary standards be adopted. The EPA/CDC study on which the determination as to whether to regulate sulfate will be based has been completed. The final decision as to whether MCLs for sulfates will be promulgated will be made by August, 2001.

Additional Information

Contact the National Technical Information Service at 1/800/553-6847 for guidance documents pertaining to sulfate.

For further information on federal drinking water requirements, contact the EPA Safe Drinking Water Hotline at 1/800/426-4791.

(See Resource Section for drinking water contacts)