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10.5 Chemical Characteristics and Constituents
are also likely to be present. The US Secondary Drinking
having turbidity of 0.2–0.3 NTU. Both the US and Canada
turbidity standards are complex. The readers are referred to
Water Standards recommend that the foaming agents be
Section 10.8 for details. Briefly speaking, the US Primary
limited to 0.5 mg/L as MBAS in drinking water. The
Drinking Water Standards require that (a) at no time can
foaming agents are not regulated by Mexican and Canadian
governments.
water treatment plant’s effluent turbidity go above 1 NTU
and (b) the filtration plants must keep the effluent turbidity
at 1 NTU or below, and must not exceed 0.3 NTU in 95% of
10.5 CHEMICAL CHARACTERISTICS AND
daily samples in any month. The Mexico MAL for turbidity
CONSTITUENTS
is 5 NTU in drinking water.
A variety of toxic substances may conceivably find their
way into water supplies, among them (a) toxic substances
10.4.3 Taste and Odor
leached from mineral formations such as fluorapatites; (b)
The words taste and odor are often used loosely and inter- phytotoxins manufactured by specific algae; (c) heavy metals
changeably. Actually there are about five tastes: sour, sweet, dissolved from waterworks structures, principally metallic
bitter, hot and salt— strictly confined in their perception to pipes and improperly manufactured plastic pipes, or added
the taste buds of the tongue. Hot is not associated with drink- as water treatment chemicals (certain polyelectrolytes, for
ing water. Odors appear to be without limit in number and instance); (d) toxic compounds contained in industrial and
are known to change in quality as the concentration of the household wastes emptied into water courses or discharged
odorous compounds, or the intensity of their smell, is varied. into the ground; (e) radioactive substances in fallout and from
However, careful screening of odors suggests that there may the nuclear energy industry; and (f) pesticides reaching water
be certain fundamental odors from which all odors could be courses from chemical dusts or sprays applied to crops and to
compounded. The smallest number in any classification is land and water surfaces for the control of agricultural blights,
four: sweet or fragrant, sour or acid, burnt or empyreumatic, nuisance insects, vectors of human and animal diseases, trash
and goaty or caprylic. fish, water weeds, and the like.
Taste and odor in water can be caused by the growth of Whereas the hazards of infective and toxic contaminants
algae or by the foreign matter such as organic compounds, are self-evident, certain qualities of water supplies touching
inorganic salts, or dissolved gases. These taste- and odor- only on the fringe of wholesomeness are not well understood.
causing substances may come from domestic, agricultural, or Excessive mineralization is one, insufficient mineralization
natural sources. Generally speaking, tastes and odors should is a second, and industrial organic chemicals are a third.
not be sufficiently intense to impress themselves on the user Some highly mineralized waters possess laxative prop-
without his knowingly searching for them. Acceptable waters erties; waters containing magnesium and sulfate ions are
should be free from any objectionable taste or odor at point examples. Other highly mineralized or hard waters consume
of water use. Legally the taste of drinking water is not regu- much soap before they form lather. The resulting causticity
lated in the United States. The US Secondary Drinking Water irritates the skin of sensitive persons, and winter chapping
Standards, however, recommend that the odor of drinking and dishpan hands may become chronic complaints.
water be 3 threshold odor number (TON) or below. Mexican Iodide and fluoride offer striking examples of insuffi-
and Canadian governments require that the taste and odor of cient mineralization. Glaciated or otherwise heavily leached
drinking water be inoffensive. soils may not contain enough iodine to satisfy physiological
requirements. Goiter is then endemic. However, the remedy
for iodine deficiency does not seem to be the introduction of
10.4.4 Temperature
iodides into drinking water, even though this was done at one
The most desirable drinking waters are consistently cool and time with apparent success. Distribution of iodide tablets to
do not have temperature fluctuations of more than a few school children and, later, the iodization of table salt have
degrees. Groundwater and surface water from mountainous proved to be fully as effective and more economical. By
areas generally meet these criteria. The most palatable water contrast, fluoridation of water for the control of dental caries
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temperature is between 50 F and 60 F(10 C–15 C). will continue to be justified until a more economical and
manageable method of furnishing physiologically needed
amounts is brought forward. Water of high sodium content,
10.4.5 Foamability
including some softened waters, may be troublesome to
Foam in water is usually caused by concentrations of persons on low-salt diets. Why soft waters appear to be
detergents greater than 1 mg/L as MBAS (methylene blue correlated with more cardiovascular disease than moderately
active substance). While foam itself is not hazardous, the hard and fluoridated waters needs further study. The mottling
user should understand that if enough detergent is reaching a of tooth enamel observed, for instance, in the mid- and south-
water supply to cause a noticeable froth to appear on a glass west United States, is caused by excessive concentrations
of water, other possibly hazardous substances of waste origin of fluorides in water. By contrast, small amounts of fluoride