Page 319 - Water Engineering Hydraulics, Distribution and Treatment

Chapter10
Water Quality Characteristics and Drinking
Water Standards
10.1 OBJECTIVES OF WATER-QUALITY which can be added, in good conscience, a lake, a spring, or
MANAGEMENT a well—“is more than an amenity, it is a treasure.”
Water-quality management is the central theme around which
revolve prescriptions for the exploitation, preservation, and 10.2 NATURAL AVAILABLE WATER
reclamation of those properties of water—physical, chemi- RESOURCES
cal, and biological—that are responsible for its extraordinary
importance in urban and industrial societies. Within the use The source of water determines its inherent quality
cycle of water in dwellings and industries, water-quality man- (Fig. 10.1). Rainwater absorbs the gases and vapors nor-
agement places upon organized communities the obligation mally present in the atmosphere (oxygen, nitrogen, carbon
to seek out waters of suitable fitness. Within the waste cycle it dioxide, and rare gases) and sweeps particulates out of the air
obliges cities, towns, and industries to send back to the com- when droplets form about them. Salt nuclei (principally chlo-
mon water resource the spent waters or wastewater effluents rides) reach the atmosphere from ocean spray and freshwater
’
of acceptable quality. Assigned to water-quality management cataracts. Once the rain wets the earth s surface, however,
thereby is a dual yet essentially unitary responsibility for both it starts to acquire the properties of surface runoff. In nor-
water supply and wastewater disposal that can prosper only mal times the composition of surface waters varies with the
when quality management establishes and honors reasonable topography and vegetation of the catchment area and with
and common objectives and necessary standards. land use and management. Both mineral and organic particu-
At one end of the quality spectrum of water lie objec- lates are picked up by erosion, together with soil bacteria and
tives and standards for safe and palatable drinking waters; other organisms, while salts and soluble substances are taken
at the other end are quality requirements for spent waters or into solution. Natural and synthetic fertilizers enter the water
wastewater effluents to be introduced into receiving bodies along with biocide residues, even though the binding power
of water or to be disposed of in other ways. Between the of soils is remarkably strong. In times of drought much of
two, there are full water quality criteria for bathing, fishing, the water flowing in surface channels is derived from rising
shellfish harvesting, and irrigation, and for industrial waters groundwater, urban dry weather runoff, and, in some loca-
of many kinds. They, too, are of concern to this chapter. tions, treated wastewater effluent. In times of flooding rain-
Water-quality management, as part of water-resource storms and snow-melt, lands not ordinarily eroded by runoff,
management, shares a need for public and technological sup- and flood plains not usually occupied by surface streams, may
port that is normally available only in a well-disciplined and contribute large amounts of silt to stream flows. Characteris-
industrially mature society. In furtherance of water quality tic additions to water in lakes and ponds are algal and other
control, moreover, there must be adequate information not growths that may produce odors and tastes. Swamp waters
only on the nature and capacity of natural sources of water contain decaying vegetation that intensifies their color, odor,
but also on their physical, chemical, and biological qual- and taste. Cities and industries add wastes of many kinds. The
ity. Within the wider meaning of water-quality management, sources of surface water supply may come from precipitation
finally, there must be an understanding by engineers of the (rain, snow, etc.), river, lake, reservoir, and ocean, as shown in
common properties of the many kinds of water on the earth: Fig. 10.1. Surface water picks up soil particles and man-made
of brooks and rivers, of lakes and oceans, and of waters substances, which are detectable as turbidity, color, chemical
welling from the ground and falling from the sky (Fig. 10.1). matters, microorganisms, and radioactive substances. Sur-
“A river,” in the words of Justice Oliver Wendell Holmes—to face water, except ocean water, is also called fresh water

Water Engineering: Hydraulics, Distribution and Treatment, First Edition. Nazih K. Shammas and Lawrence K. Wang.
© 2016 John Wiley & Sons, Inc. Published 2016 by John Wiley & Sons, Inc.

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