Page 24 - Water Engineering Hydraulics, Distribution and Treatment

2
Chapter 1
US public water systems size by population served in 2007
Table 1.1
Large
Very small
Very large
Medium
Small
(>100,000)
Total
(500 or less)
Water system
4,822
3,702
29,282
Community
13,906
52,110
398
No. of systems
a
105,195,727
27,942,486
water system
4,857,007
Population
19,848,329
served
27
Percentage of
9
1
7
100
56
systems
100
45
Percentage of
37
10
7
population
2,662
16,034
Nontransient
120
22
1
18,839
No. of systems
2,710,330
2,247,556
203,000
Population
noncommunity Introduction to Water Systems 2 (501–3,300) (3,301–10,000) (10,001–100,000) 128,607,655 286,451,204
533,845
639,561
6,334,292
water system b served
Percentage of 85 14 1 0 0 100
systems
Percentage of 35 43 10 8 3 100
population
Transient No. of systems 81,873 2,751 102 15 3 84,744
noncommunity Population 7,230,344 2,681,373 546,481 424,662 2,869,000 13,751,860
water system c served
Percentage of 97 3 0 0 0 100
systems
Percentage of 53 19 4 3 21 100
population
Total no. of systems 127,189 19,319 5,044 3,739 402 155,693
Source: Courtesy US Environmental Protection Agency.
a Community water system: a public water system that supplies water to the same population year-round.
b Nontransient noncommunity water system: a public water system that regularly supplies water to at least 25 of the same people at least 6 months per year,
but not year-round. Some examples are schools, factories, office buildings, and hospitals that have their own water systems.
c Transient noncommunity water system: a public water system that provides water in a place such as a gas station or campground where people do not
remain for long periods of time.
The collected wastewaters are treated and reused or dis- adequacy, seasonal and, in large developments, even annual
charged, usually into a natural water body, more rarely onto surpluses must be stored for use in times of insufficiency.
land. Often the receiving body of water continues to serve When the quality of the water collected is not satisfactory,
also as a source of important water supplies for many pur- purification works are introduced to render it suitable for
poses. It is this multiple use of natural waters that creates the the purposes it must serve: contaminated water is disin-
most impelling reasons for sound water quality management. fected; aesthetically displeasing water made attractive and
palatable; water containing iron or manganese deferrized or
demanganized; corrosive water deactivated; and hard water
1.1 COMPONENTS OF WATER SYSTEMS softened. Transmission works convey the collected and
purified supply to the community, where distribution works
Each section of this chapter offers, in a sense, a preview of dispense it to consumers in wanted volume at adequate
matters discussed at length in later parts of this book. There pressure. Ordinarily, the water delivered is metered so that
they are dealt with as isolated topics to be mastered in detail. an equitable charge can be made for its use and, often, also
Here they appear in sequence as parts of the whole so that for its disposal after use.
their general purpose and significance in the scheme of things
may be understood and may give reason for closer study.
Municipal water systems generally comprise (a)
1.2 REQUIRED CAPACITY
collection works,(b) purification works,(c) transmission
works, and (d) distribution works. The relative functions and Water supply systems are designed to meet population needs
positions of these components in a surface water supply are for a reasonable number of years in the future. The rate of
sketched in Fig. 1.1. Collection works either tap a source consumption is normally expressed as the mean annual use
continuously adequate in volume for present and reasonable in gpcd or Lpcd, and seasonal, monthly, daily, and hourly
future demands or convert an intermittently insufficient departures in rate are given in percentages of the mean. In
source into a continuously adequate supply. To ensure North America the spread in consumption is large: from