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130 Chapter 4 Quantities of Water and Wastewater Flows
is clean, palatable, and of unquestioned safety; soft for washing and cool for drinking; and
generally useful to industry. The availability of groundwater and nearby surface sources
may persuade large industries and commercial enterprises to develop their own process
and cooling waters.
Hydraulically, leaks from mains and plumbing systems and flows from faucets and
other regulated openings behave like orifices. Their rate of flow varies as the square root
of the pressure head, and high distribution pressures raise the rate of discharge and with
it the waste of water from fixtures and leaks. Ordinarily, systems pressures are not raised
2
above 60 psig (lb/in. gage), or 416 kPa, in American practice, even though it is impos-
sible to employ direct hydrant streams in firefighting when hydrant pressures are below
75 psig (520 kPa).
Metering encourages thrift and normalizes the demand. The costs of metering and
the running expense of reading and repairing meters, however, are substantial. They may
be justified in part by accompanying reductions in waste and possible postponement of
otherwise needed extensions. Under study and on trial here and there is the encourage-
ment of off-peak-hour draft of water by large users. To this purpose, rates charged for
water drawn during off-peak hours are lowered preferentially. The objective is to reap
the economic benefits of a relatively steady flow of water within the system and the re-
sulting proportionately reduced capacity requirements of systems components. The
water drawn during off-peak hours is generally stored by the user at ground level even
when this entails repumping.
Distribution networks are seldom perfectly tight. Mains (see Fig. 4.3), valves, hy-
drants, and services of well-managed systems are therefore regularly checked for leaks.
Superficial signs of controllable leakage are:
1. High night flows in mains
2. Water running in street gutters
3. Moist pavements
4. Persistent seepage
5. Excessive flows in sewers
6. Abnormal pressure drops
7. Unusually green vegetation (in dry climates)

Figure 4.3 Water Leakage from a Crack in a Water Pipe.