Page 135 - Water Loss Control

Identifying Economic Interventions against W ater Losses 117

Use the IWA water balance to
calculate the current annual
real losses

Measure system pressures: Calculate unavoidable annual real
check for the presence of surges, losses (UARL) using average
identify excess pressure above minimum system pressure
standard of service, and any pressure
below the minimum standard of service

Calculate the
Identify opportunities for achieving infrastructure leakage index
economic management of operating ILI = CARL/UARL
pressures, to reduce frequencies of new
leaks, and flow rates of running leaks

Calculate economic intervention times
Operate to economic ALC and economic annual real losses
intervention times (EARL) using cost of water

Calculate the
Identify economic speed and economic leakage index
quality of repairs
ELI = CARL/EARL

Benchmark the operational performance
Identify opportunities for achieving in managing real losses by comparing
economic infrastructure management the ILI and ELI with international,
activities: assets, mains and national and sub-system data
service connections UARL< CARL < EARL

FIGURE 9.7 Practical application—fl owchart. (Source: Allan Lambert/Dave Pearson.)

Throughout the leakage reduction plan, the performance of the network should
10
be assessed using the IWA ILI approach and information systems should be set up
to collect data on the topography, pressure regime, burst frequencies, and so on so
that more detailed analysis of ELL can be carried out as reductions in leakage are
made. Whereas initial estimates of ELL will rely on default values and assumptions,
the calculations can be refined using actual data from the specific operations which
are implemented.
This approach can be described by a flowchart (Fig. 9.7).

9.8 Summary
For any system, the economic level of leakage is that which results from a combination
of a range of leakage management activities that comprises (in priority)