The IWA's Task Force on Unaccounted-for Water (UFW) had two key objectives. The first—Recommendations for a standard international terminology for calculation of real and apparent losses from water balance—is presented as a Blue Pages [1]. As the second—to review performance indicators (PIs) for international comparisons of losses in water supply systems—is only briefly mentioned in the Blue Pages, this AQUA paper explains the technical basis for the task force's recommendations on PIs for real (physical) losses. Traditional PIs were checked against several key local factors which constrain performance in managing real losses. ‘Number of service connections’ was found to be the most consistent of the traditional PIs over the greatest range of density of service connections, and is recommended as the preferred basic traditional technical indicator for real losses (TIRL). However, TIRL does not take account of several key local factors. To overcome this deficiency, TIRL should be compared with an estimate of unavoidable annual real losses (UARL). An auditable component-based approach is developed and satisfactorily tested for predicting UARL for any system, taking into account the local factors and using international data. The infrastructure leakage index (ILI), calculated as the ratio of TIRL to UARL, is a nondimensional PI, which enables overall infrastructure management performance in control of real losses to be assessed independently of the current operating pressures; minimum achievable operating pressures are usually constrained by local topography and standards of service.

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