Page 81 - Water and wastewater engineering

2-24 WATER AND WASTEWATER ENGINEERING

Chloride. Most waters contain some chloride. The amount present can be caused by the leach-
ing of marine sedimentary deposits or by pollution from sea water, brine, or industrial or domestic
wastes. Chloride concentrations in excess of about 250 mg/L usually produce a noticeable taste in
drinking water. Domestic water should contain less than 100 mg/L of chloride to be palatable.

Fluoride. In some areas, water sources contain natural fluoride. Where the concentrations
approach optimum levels, beneficial health effects have been observed. In such areas, the
incidence of dental caries (tooth decay) has been found to be below the 1evels observed in areas
without natural fluoride. Many cities choose to add fluoride to the water supply to reduce the
incidence of dental caries. The optimum fluoride level for a given area depends upon air tem-
perature because temperature greatly influences the amount of water people drink. Excessive
fluoride in drinking water supplies may produce fluorosis (mottling) of teeth, * which increases
as the optimum fluoride level is exceeded.

Iron. Small amounts of iron frequently are present in water because of the large amount of iron
in the geologic materials. The presence of iron in water is considered objectionable because it
imparts a reddish color to the water, stains bathroom fixtures and laundered goods with a yellow
to reddish-brown color, and affects the taste of beverages such as tea and coffee.

Lead. Lead occurs in drinking water primarily from corrosion of lead pipes. Lead exposure is
associated with a large number of pathological effects including but not limited to interference
with red blood cell formation, kidney damage, and impaired cognitive performance.

Manganese. Naturally occurring manganese is often present in significant amounts in ground-
water. Anthropogenic sources include discarded batteries, steel alloy production, and agricultural
products. It imparts a dark brown or black color to water and stains fixtures and cloth that is
washed in it. It flavors coffee and tea with a medicinal taste.

Sodium. The presence of sodium in water can affect persons suffering from heart, kidney,
or circulatory ailments. When a strict sodium-free diet is recommended, any water should be
regarded with suspicion. Home water softeners may be of particular concern because they add
large quantities of sodium to the water.

Sulfate. Waters containing high concentrations of sulfate, caused by the leaching of natural
deposits of magnesium sulfate (Epsom salts) or sodium sulfate (Glauber’s salt), may be undesir-
able because of their laxative effects.

Zinc. Zinc is found in some natural waters, particularly in areas where zinc ore deposits have
been mined. Zinc is not considered detrimental to health, but it will impart an undesirable taste
to drinking water.

Toxic Inorganic Substances. Nitrates (NO ), cyanides (CN ), and heavy metals constitute
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the major classes of inorganic substances of health concern. Methemoglobinemia (infant cyano-
sis or “blue baby syndrome”) has occurred in infants who have been given water or fed formula
prepared with water having high concentrations of nitrate. Cyanide ties up the hemoglobin sites
that bind oxygen to red blood cells. This results in oxygen deprivation. A characteristic symptom

*Mottled teeth are characterized by black spots or streaks and may become brittle when exposed to large amounts of fluoride.