Iwaawwa Recommended Performance Indicators for Nonrevenue Water and Real Losses

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During the period 1996 to 2000, various IWA Task Forces undertook a detailed study to determine the most appropriate performance indicators for different water supply purposes. Table 7.4 below shows the PIs for nonrevenue water and real losses recommended by IWA1,2,8 converted to North American units.

The PIs are categorized by function and by level, defined as follows:

• Level 1 (basic): A first layer of indicators that provide a general management overview of the efficiency and effectiveness of the water undertaking.

Function

Ref.

Level

Performance Indicator

Comments

Financial: nonrevenue water by volume

Fi36

1 (basic)

Volume of nonrevenue water as % of system input volume

Can be calculated from simple water balance

Financial: nonrevenue water by cost

Fi37

3 (detailed)

Value of nonrevenue water as % of annual cost of running system

Allows different unit costs for nonrevenue water components

Inefficiency of use of water resources

WR1

1 (basic)

Real losses as a % of system input volume

Unsuitable for assessing efficiency of management of distribution systems

Operational: real losses

Op24

1 (basic)

gal/service line/d, when system is pressurized

Best "traditional" basic performance indicator

Operational: real losses

Op25

3 (detailed)

Infrastructure leakage index

Ratio of current annual real losses to unavoidable annual real losses

Table 7.4 IWA Recommended Performance Indicators for Nonrevenue Water and Water Losses

Table 7.4 IWA Recommended Performance Indicators for Nonrevenue Water and Water Losses

• Level 2 (intermediate): Additional indicators, which provide a better insight than the Level 1 indicators for users who need to go further in depth.

• Level 3 (detailed): Indicators that provide the greatest amount of specific detail, but are still relevant at the top management level.

Particular points to note from the Table 7.4 are as follows:

• Fi36: Percentage of nonrevenue water is the basic financial PI.

• Fi37: This detailed financial PI is a development of a 1996 recommendation of the AWWA Leak Detection and Water Accountability Committee.

• WR1: Real losses as percentage are unsuitable for assessing efficiency of management of distribution systems for control of real losses, because of the influence of consumption.

• Op24: Gallons/service line/d is the most reliable of the traditional PIs for real losses, for all systems with service line densities of > 32/mile.

• To improve on Op24, take account of three key system-specific factors: Density of service connections, location of customer meter relative to curbstop, average operating pressure.

NOTE: By expressing Op 24 as "Gallons/service line/d/psi of pressure," the influence of pressure is included.

• Op25: The infrastructure leakage index (ILI) is a measure of how well the system is being managed for the control of real losses, at the current operating pressure.

• ILI: It is a dimensionless ratio between the current annual real losses (CARL) based on the results of the water balance and the unavoidable annual real losses (UARL) for a given system.

• UARL: They are calculated as previously described in this chapter, using the IWA methodology which takes into account average operating pressure, length of mains, number of service lines, and location of customer meters relative to the curb stop.

The infrastructure leakage index is a relatively new, and potentially very useful, performance indicator. Being a ratio, it has no units, so facilitates comparisons between countries that use different measurement units (metric, U.S. Customary). The ILI can perhaps be better envisaged from Fig. 7.5, which shows the four components of leakage management.

The large square represents the current annual volume of leakage, which is always tending to increase, as infrastructure systems grow older. This increase, however, can be constrained by an appropriate combination of the four components of a successful leakage management policy.

The small square represents UARL—the lowest technically achievable value for real losses at the current operating pressure. The ratio of the current annual real losses (the large square) to the unavoidable annual real losses (the small square) is a measure of how well the three infrastructure management functions—repairs, pipe materials management, and active leakage control—are being controlled. We will be seeing more of this diagram in future chapters where we will be discussing some of the hands-on techniques associated with in the field loss-reduction programs.

Leakage Management Iwa
Figure 7.5 The four components of a successful leakage management policy. (Source: IWA Water Loss Task Force and AWWA Water Loss Control Committee)

he ILI ratio is a great way of demonstrating loss management performance, as each system effectively compares the ratio of their individual best possible performance against how they are actually performing.

An infrastructure leakage index close to 1.0 demonstrates that all aspects of a successful leakage management policy are being implemented by a water utility. However, typically it will only be economic to achieve an ILI close to 1.0 if water is very expensive, scarce, or both. Economic values of ILI depend upon the system-specific marginal cost of real losses, and typically lie in the range 1.5 to 2.5 for most systems.

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