Page 102 - Water Loss Control

84 Cha pte r Se v e n

in a considerable amount of leakage being written off as beyond control. In fact, there
are infrastructure and pressure management options that now exist to reduce it.
A similar situation applies regarding discovered leaks from pressurized pipework and
overflows from service reservoirs. The most common practice in countries outside North
America is to calculate the annual volume of water losses from the water balance with-
out making any deductions for unavoidable leakage or discovered leaks and overflows,
and then to calculate the performance indicators. Accordingly, superficial comparisons
of North American water losses with water losses from other countries often present a
more favourable picture than is actually the case.
The IWA and AWWA recommended standard methodology for water audit calcula-
tions and performance indicators allows unavoidable losses and discovered leaks and overflows
to be considered, but only as partial explanations of the total volume of water losses, which
should always be explicitly stated before attempting to explain or justify the total volume.
The IWA system–specific approach to unavoidable annual real losses is described in the
next section.

7.5.1 The IWA Approach to Calculating Unavoidable Annual Real Losses
The IWA approach is described in detail in the December 1999 issue of the IWA AQUA
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Magazine, and can be seen as a natural development of previous North American attempts
to take key local factors into account. The component-based approach is based on auditable
assumptions for break frequencies, flow rates, durations; background and breaks estimates
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concepts to calculate the components of unavoidable real losses for a system with well-
maintained infrastructure; speedy good-quality repairs of all detectable leaks and breaks;
and efficient active leakage control to locate unreported leaks and breaks.
Parameters used in the calculation, taken from “Water Loss Management in North
America” and converted to North American units, are shown in Table 7.1. Table 7.2
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shows these parameters in a more user-friendly format for calculation purposes.

Background
Infrastructure (Undetectable)
Component Losses Reported Breaks Unreported Breaks
Mains 8.5 gal/mi/hr 0.20 breaks/mi/year 0.01 breaks/mi/year
at 50 gpm for 3 days at 25 gpm for 50 days
duration duration
Service lines, main 0.33 gals/service 2.25/1000 service 0.75/1000 service
to curb stop line/hr line/year at 7 gpm line/year at 7 gpm
for 8 days duration for 100 days duration
Underground pipes, 0.13 gal/service 1.5/1000 service 0.50/100 service
curb stop to meter line/hr line/year at 7 gpm line/year at 7 gpm
(for 50 ft ave. for 9 days duration for 101 days duration
length)

gal = U.S. gallon; all flow rates are at a reference pressure of 70 psi
Source: Ref. 7.
TABLE 7.1 Parameters Values Used for Calculation of Unavoidable Annual Real Losses (UARL)