Jump to main content or area navigation.

Contact Us

Water: Unregulated

Sulfate in Drinking Water


Sulfate is a substance that occurs naturally in drinking water. Health concerns regarding sulfate in drinking water have been raised because of reports that diarrhea may be associated with the ingestion of water containing high levels of sulfate. Of particular concern are groups within the general population that may be at greater risk from the laxative effects of sulfate when they experience an abrupt change from drinking water with low sulfate concentrations to drinking water with high sulfate concentrations.

Sulfate in drinking water currently has a secondary maximum contaminant level (SMCL) of 250 milligrams per liter (mg/L), based on aesthetic effects (i.e., taste and odor). This regulation is not a Federally enforceable standard, but is provided as a guideline for States and public water systems. EPA estimates that about 3% of the public drinking water systems in the country may have sulfate levels of 250 mg/L or greater.

The Safe Drinking Water Act (SDWA), as amended in 1996, directs the U.S. Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC) to jointly conduct a study to establish a reliable dose-response relationship for the adverse human health effects from exposure to sulfate in drinking water, including the health effects that may be experienced by sensitive subpopulations (infants and travelers). SDWA specifies that the study be based on the best available peer-reviewed science and supporting studies, conducted in consultation with interested States, and completed in February 1999.

Top of page


EPA and CDC completed a study, Health Effects from Exposure to High Levels of Sulfate in Drinking Water Study ("Sulfate Study") in January, 1999. The overall purpose of this study was to examine the association between consumption of tap water containing high levels of sulfate and reports of osmotic diarrhea in susceptible populations (infants and transients). Specifically, CDC researchers designed field investigations of infants naturally exposed to high levels of sulfate in the drinking water provided by public water systems and an experimental trial of exposure in adults.

As a supplement to the Sulfate Study and literature review, CDC, in coordination with EPA, convened an expert workshop ("Sulfate Workshop"), open to the public, in Atlanta, Georgia on September 28, 1998. The expert scientists reviewed the available literature and the Sulfate Study results, and provided their opinions in response to a series of questions about the health effects from exposure to sulfate in drinking water.

EPA announced the availability of the Sulfate Study report and the Sulfate Workshop summary in the Federal Register.

Top of page

Next Steps

Sulfate is one of the 50 chemical and 10 microbiological contaminants/contaminant groups included on the Drinking Water Contaminant Candidate List published on March 2, 1998 (63 FR 10273). SDWA, section 1412 (b)(12)(B)(ii), directs EPA to include sulfate among the five or more contaminants for which the Agency will determine by August, 2001, whether or not to regulate.

EPA will be further evaluating the two documents, analyzing all public comments on the documents, reviewing all comments on its previously proposed National Primary Drinking Water Regulation for sulfate (December 20, 1994; 59 FR 65578) and reviewing any other pertinent information that could have a bearing on its decision of whether or not to regulate sulfate as a NPDWR. In so doing, EPA will be evaluating whether or not the statutory tests provided at Section 1412(b)(1)(A) of SDWA for proceeding with such regulation are met:

  • "....the contaminant may have an adverse effect on the health of persons;
  • the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern; and
  • in the sole judgment of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems."

In making this determination, EPA will review, in addition to the dose-response data and information described in the Federal Register notice a host of applicable risk management factors, including, but not limited to: occurrence data on concentrations of sulfate in public water systems; information relative to treatment technologies (particularly, technologies applicable to small public water systems); availability and costs of analytical methods for sulfate; and overall costs and benefits attributable to any likely rule.

Top of page

Jump to main content.