Page 40 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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1.1 Components of Water Systems 3
water system. Of the approximately 52,000 community water systems, just 8% of those
systems (4,048) serve 82% of the people.
Water is used in population centers for many purposes: (a) for drinking and culi-
nary uses; (b) for washing, bathing, and laundering; (c) for cleaning windows, walls,
and floors; (d) for heating and air conditioning; (e) for watering lawns and gardens;
(f) for sprinkling and cleaning streets; (g) for filling swimming and wading pools; (h) for
display in fountains and cascades; (i) for producing hydraulic and steam power; (j) for
employment in numerous and varied industrial processes; (k) for protecting life and
property against fire; and (l) for removing offensive and potentially dangerous wastes
from households, commercial establishments, and industries. To provide for these vary-
ing uses, which total about 100 gallons per capita per day (gpcd) or 378 liters per capita
per day (Lpcd) in average North American residential communities and 150 gpcd (568
Lpcd) or more in large industrial cities, the supply of water must be satisfactory in
quality and adequate in quantity, readily available to the user, relatively cheap, and eas-
ily disposed of after it has served its many purposes. Necessary engineering works are
waterworks, or water supply systems, and wastewater works, or wastewater manage-
ment systems.
Waterworks withdraw water from natural sources of supply, purify it if necessary, and
deliver it to the consumer. Wastewater works collect the spent water of the community—
about 70% of the water supplied—together with varying amounts of entering ground and
surface waters. The collected wastewaters are treated and reused or discharged, usually
into a natural water body; more rarely onto land. Often the receiving body of water contin-
ues to serve also as a source of important water supplies for many purposes. It is this mul-
tiple use of natural waters that creates the most impelling reasons for sound water quality
management.

1.1 COMPONENTS OF WATER SYSTEMS
Each section of this chapter offers, in a sense, a preview of matters discussed at length in
later parts of this book. There they are dealt with as isolated topics to be mastered in detail.
Here they appear in sequence as parts of the whole so that their general purpose and signif-
icance in the scheme of things may be understood and may give reason for closer study.
Municipal water systems generally comprise (a) collection works, (b) purification
works, (c) transmission works, and (d) distribution works. The relative functions and po-
sitions of these components in a surface water supply are sketched in Fig. 1.1. Collection
works either tap a source continuously adequate in volume for present and reasonable
future demands or convert an intermittently insufficient source into a continuously ade-
quate supply. To ensure adequacy, seasonal and, in large developments, even annual sur-
pluses must be stored for use in times of insufficiency. When the quality of the water col-
lected is not satisfactory, purification works are introduced to render it suitable for the
purposes it must serve: Contaminated water is disinfected; aesthetically displeasing
water made attractive and palatable; water containing iron or manganese deferrized or
demanganized; corrosive water deactivated; and hard water softened. Transmission
works convey the collected and purified supply to the community, where distribution
works dispense it to consumers in wanted volume at adequate pressure. Ordinarily, the
water delivered is metered so that an equitable charge can be made for its use and, often,
also for its disposal after use.