Calculating Losses from Reported and Unreported Breaks

After collecting the annual numbers of reported breaks on mains and service connections (and other system components such as valves and hydrants if so desired), flow rates and durations have to be established. Unless the utility has investigated average leak flow rates and has detailed data available the figures from Table 10.8 can be used as a starting point.

The break/leak duration can be split in three elements—time needed for

Awareness duration: The length of time taken from a leak first occurring—whether it is reported or unreported—to the time when the utility first becomes aware that a leak exists, although not necessarily aware of its exact location. For reported leaks and breaks, this duration is usually very short, while for unreported leaks and breaks, it is a function of the active leakage control policy interventions.

Location of Break

Flow Rate for Reported Breaks [gal/hr/psi pressure]

Flow Rate for Unreported Breaks [gal/hr/psi pressure]

Mains

44

22

Service connection

6

6

Source: Julian Thornton, Reinhard Sturm, George Kunkel, P.E

Table 10.8 Example Reported and Unreported Leakage Flow Rates

Source: Julian Thornton, Reinhard Sturm, George Kunkel, P.E

Table 10.8 Example Reported and Unreported Leakage Flow Rates

Location duration: For reported leaks and breaks, this is the time it takes for the water utility to investigate the report of a leak or break and to correctly locate its position so that a repair can be effected; for unreported leaks and breaks, the location duration is zero since the leak or break is detected during the leak detection survey and awareness and location occur simultaneously.

Repair duration: The time it takes to make the repair or shut off once a leak has been located.

The overall volume of water lost through each running break and leak is determined from the overall time of these three components and the flow rate of the leak at the current system pressure. This is shown graphically in Chap. 17.

The water balance calculates the total volume of real losses for the audit year. However, it does not provide the information on what portion of these real losses is due to background losses, reported losses, and unreported losses.

By assessing the volume of real losses through component-based analysis, it is possible to model the volume of real losses that are due to each component and identify suitable tools for their reduction.

A more in-depth analysis of components of real loss may include an analysis of the frequency of breaks on different system components against the baseline UARL frequencies, which in conjunction with measured ICF values might help to dictate the longer term need for infrastructure replacement.

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