SO4, Sulfate, is found in most natural waters and also enters water via industrial waste. Sulfate is even found as a dissolved constituent of rainwater.

Large amounts of sulfate in drinking water can cause a laxative effect.

Bacteria which feed on sulfate are the main cause of hydrogen sulfide H2S .

EPA has set a secondary standard of 250 mg/l for sulfate.

Treatment: Sulfate is easily removed by reverse osmosis (97 to 98%), and sulfates can also be reduced by a strong base anion exchanger.