Page 37 - Water Engineering Hydraulics, Distribution and Treatment

1.10 Water Systems Management
Service or
curb box
Street
Foundation wall
Supply to
Frost
building
depth
Corporation
Stop and waste cock
cock or stop
Caulked
Check
Goose neck
Figure 1.10 Service pipe, fittings,
pipe
valve
Union
Union
Drip
and accessories. There are many
sleeve
valve
possible modifications, both inside
Curb cock
Testing
Valve
Meter
Valve
and outside the building. In many
Street
Service pipe
tee
or stop
Hose end
main
instances, the meter is conveniently
placed in a vault outside the 15
Basement floor building.
a small area, are generally equipped with high-pressure fire the take-offs to the various plumbing fixtures or other points
supplies and distribution networks of their own. Because such of water use is illustrated in Fig. 1.10. Small services are
supplies may be drawn from sources of questionable quality, made of cement-lined iron or steel, brass of varying cop-
some regulatory agencies enforce rigid separation of private per content, admiralty metal, copper, and plastics such as
fire supplies and public systems. Others prescribe protected polyethylene (PE), high-density polyethylene (HDPE), or
cross-connections that are regularly inspected for tightness. polyvinyl chloride (PVC). Because lead and lead-lined pipes
Ground-level storage and pumping are less advantageous. may corrode and release lead to the water, they are no longer
installed afresh. For large services, coated or lined CIP is
often employed. For dwellings and similar buildings, the
1.9.3 Pressures
3
minimum desirable size of service is ∕ in. (19 mm). Pipe-
4
In normal municipal practice, pressures of 60–75 psig (416– tapping machines connect services to the main without shut-
520 kPa) are maintained in business blocks and 40 psig ting off the water. They also make larger connections within
(278 kPa) in residential areas. Higher pressures, such as water distribution systems.
100 psig (694 kPa) or more, delivering adequate amounts
of water for firefighting through hoses attached directly to
fire hydrants are no longer important. Instead, modern motor 1.10 WATER SYSTEMS MANAGEMENT
pumpers can discharge thousands of gallons per minute at
Construction of water supplies from the ground up, or their
even greater pressures. Moreover, low operating pressures
improvement and extension, progresses from preliminary
make for low leakage from mains and reduce the amount
investigations or planning through financing, design, and
of water that is unaccounted for. To supply their upper sto-
construction to operation, maintenance, and repair. Political
ries, tall buildings boost water to tanks at various elevations
and financial procedures are involved as well as engineering.
and on their roofs or in towers. In individual industrial com-
plexes, the water pressure may be raised during fires by fixed
installations of fire pumps. 1.10.1 Municipal Supplies
The cost of public water supplies in the United States pro-
1.9.4 Capacity
vides the reader with some concept of the magnitude of
The capacity of distribution systems is dictated by domestic, engineering activity and responsibility associated with their
industrial, and other normal water uses and by the standby design and construction. Per capita investment in physical
or ready-to-serve requirements for firefighting. Pipes should plant depends on many factors: nature, proximity, and abun-
be able to carry the maximum coincident draft at velocities dance of suitable water sources; need for water treatment;
that do not produce high pressure drops and water ham- availability and price of labor and materials; size and con-
mer. Velocities of 2–4 ft/s (0.60–1.2 m/s) and minimum pipe struction conditions of the system; habits of the people; and
diameters of 6 in. (150 mm) are common in North American characteristics of the areas served. Wide differences in these
municipalities. factors make for much variation in initial costs. For commu-
nities in excess of 10,000 population, replacement costs in
North America lie in the vicinity of $1,500 per capita (for
1.9.5 Service to Premises
2008 price levels; for other years multiply by the ratio of an
Water reaches individual premises from the street main applicable utilities price index; see Appendix 16), with much
through one or more service pipes tapping the distribution of the investment in small communities chargeable to fire
system. The building supply between the public main and protection.