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<br />. . <br /> <br />. . . . <br /> <br />. <br /> <br />Recommended <br />maximum <br />ppm .!! <br />1.5 <br />.3 <br />125 <br />250 <br />250 J./ <br />500 <br /> <br />Constituent <br /> <br />Fluoride . . . . '. . . . . . . . . . <br />Iron plus manganese. . . . . . <br />Magnesium. . . . . . <br />Chloride . . . . . . . . . . . . <br />Sulfate . . . . <br />Dissolved solids . . . . . . . . . <br /> <br />.!! Mandatory. <br />11 <br /> <br />. . . . . . <br /> <br />. . . <br /> <br />. . <br /> <br />. . <br /> <br />. <br /> <br />. . <br /> <br />. . . <br /> <br />. . <br /> <br />. . <br /> <br />. . <br /> <br />. . <br /> <br />. . . <br /> <br />. . <br /> <br />. . . <br /> <br />. . <br /> <br />. . <br /> <br />1,000 ppm permitted if water of better quality is not <br />available. <br /> <br />< <br /> <br />Fluoride in drinking water has become a subject of public <br />interest because of the effects that different concentrations <br />may have on tooth development. According to Welsh and Thomas <br />(1960, p. 289-300), concentrations between 0.6 and 1.2 ppm are <br />beneficial in preventing decay of children's teeth: however, <br />concentrations in excess of 1.5 ppm may cause mild mottling of <br />teeth especially in children, and concentrations in excess of <br />6 ppm may cause severe mottling. Fluoride can be added to the <br />water easily and at a relatively low cost, but removal of <br />fluoride from water is difficult and, at present, expensive. <br /> <br />Iron and manganese may affect the taste of water so that <br />it is impotable, or they may form deposits that discolor the <br />water and food products. Iron bacteria, which thrive in water <br />containing high concentrations of iron, can affect the taste, <br />odor, and color of the water. Iron and manganese in water, <br />upon being exposed to air, are oxidized and form preCipitates <br />that cause water to become cloudy. Because of the oxidation, <br />surface waters ordinarily contain less iron and manganese in <br />solution than ground waters. Iron can be removed from water <br />by either of two basic methods--chemical treatment and filtration <br />or direct oxidation and filtration. Some manganese usually is <br />removed simultaneously with iron: however, manganese is IlIOre <br />difficult to remove than iron and may require special procedures. <br /> <br />Magnesium and sulfate in high concentrations in water may <br />have cathartic effects, particularly on those not accustomed to <br />the water. However, consumption of the water at concentrations <br />high enough to be harmful ordinarily would be prevented by the <br />disagreeable taste. Magnesium can be removed from water by the <br />usual softening methods. <br /> <br />High concentrations of chloride may impart a salty taste <br />to water: concentrations up to 250 ppm are not objectionable <br />for most people, but taste preception differs with individuals. <br />Although chloride in drinking water helps replace chloride lost <br />through perspiration, high concentrations may be harmful to <br /> <br />23 <br />