(4) Chloride. Cehloride exits in most natural waters. It is the main anion found in
seawater. Chloride comes from natural salt deposits, domestic and industrial wastes, and agricultural
runoff. Even in low concentrations, chloride can produce an objectionable taste in water.
(5) Sulfates. Sulfates occur naturally in water as the result of dissolution of sulfurbearing
minerals. Significant concentrations also result from industry sources, such as coalmine drainage, pulp
paper mills, tanneries, textile mills, and domestic wastewater. When ingested sulfates have a laxative
effect. They also can produce a bad taste in water.
(6) Hardness characteristics due to dissolved minerals. Hardness is caused by the soluble
salts of calcium, magnesium, iron, manganese, sodium, sulfates, chlorides, and nitrates. The degree of
hardness depends on the type and on the amount of impurities present in the water. Hardness also
depends on the amount of carbon dioxide in solution. Carbon dioxide influences the solubility of the
impurities that cause hardness. The hardness caused by carbonates and bicarbonates is called carbonate
hardness. The hardness caused by all others (chlorides, sulfates, and nitrates) is called noncarbonate
hardness. Hardness is undesirable in that it consumes soap, makes water less satisfactory for cooking,
and produces scale in boilers and distillations units. Magnesium is the eighth most abundant element on
earth. It is a principal cation contributing to water hardness. When ingested in moderate doses,
magnesium acts as a laxative. The following minerals cause hardness in ground and surface waters:
(a) Calcium carbonate. It is alkaline and only slightly soluble. It causes carbonate
hardness and alkalinity in water.
(b) Calcium bicarbonate. It contributes to the alkalinity and carbonate hardness of
water. Calcium bicarbonate when heated produces carbon dioxide and calcium carbonate.
Calcium sulfate or gypsum. It causes non-carbonate hardness in water.
(d) Calcium chloride. It causes noncarbonate hardness in water. In steam boilers and
distillation units, the presence of calcium chloride can cause chemical reactions, which result in pitting
of the boiler tubes.
(e) Magnesium carbonate and magnesium bicarbonate. They act the same in water as
calcium carbonate and bicarbonate.
(f) Magnesium sulfate. It adds to noncarbonate hardness of water and causes boiler
scale. In amounts greater than 500 PPM in drinking water, it acts as a laxative.
(g) Magnesium chloride. It has the same properties and effects as calcium chloride.
However, the magnesium will contribute to the formation of magnesium hydroxide.
Other characteristics due to dissolved minerals.