CHLORIDE AND SULFATE

Almost all natural waters contain chloride and sulfate ions. Their concentrations vary considerably according to the mineral content of the earth in any given area. In small amounts they are not significant. In large concentrations they present problems. Usually chloride concentrations are low. Sulfates can be more troublesome because they generally occur in greater concentrations. Low to moderate concentrations of both chloride and sulfate ions add palatability to water. In fact, they are desirable for this reason. Excessive concentrations of either, of course, can make water unpleasant to drink.

The EPA Secondary Drinking Water Regulations recommend a maximum concentration of 250 mg/1 for chloride ions and 250 mg/1 for sulfate ions (expressed as Cl- and S0₄--, not as CaC0₃).

Water containing calcium sulfate ions is likely to have a characteristic taste ... somewhat bitter and astringent. In fact, it has been compared to the way dissolved gypsum might taste in water. When 30 to 40 grains per gallon of calcium sulfate are dissolved in water, most people can detect the taste.

If equal amounts of magnesium sulfate or sodium sulfate are dissolved in water, the taste would not be noticeable. Both possess definite laxative effects in concentrations above 30 grains per gallon. In this way, they can be troublesome especially to people not accustomed to such water. In addition to their laxative properties and possible medicinal taste, sulfate water can mean extreme hardness, large amounts of sodium salts or acidity. Alone or together, these can pose special problems in the conditioning of water.

Chlorides give water a salty taste. At what concentrations does chlorine become noticeable? It depends upon the individual. In large concentrations chlorides cause a brackish, briny taste that definitely is undesirable. Although chlorides are extremely soluble, they possess marked stability. This enables them to resist change and to remain fairly constant in any given water unless the supply is altered by dilution or by industrial or human wastes. Both chlorides and sulfates contribute to the total mineral content of water. As indicated above, the total concentration of minerals may have a variety of effects in the home. High concentrations of either sulfate or chloride ions add to the electrical conductivity of water.

Chlorides and sulfates can be substantially removed from water by reverse osmosis. Deionization (demineralization) or distillation will also remove chlorides and sulfates from water, but these methods are less suitable for household use than reverse osmosis.