Methodological challenges in applying the infrastructure leakage index (ILI) to water utilities in Rhineland-Palatinate (Germany)

ABSTRACT Bar chart showing the sensitivity of the infrastructure leakage index (ILI) to structural influences on UARL estimation (A1-A6), factors affecting UARL estimation (B1-B3), and uncertainties affecting CARL estimation (C1-C3). Bars show the change in ILI relative to the baseline value of 0.69. A1 and A2 represent qualitative effects and are not expressed as quantitative bar values. The infrastructure leakage index (ILI) is recognised as a key indicator for assessing water losses, yet its practical application in Germany remains limited. Using data from 67 water utilities in Rhineland-Palatinate, this paper investigates why many utilities report low ILI values and analyses structural and data-related factors contributing to this pattern. By applying correction approaches such as the fixed and variable area discharges concept, pressure–burst adjustments, Poisson adjustments, and the system correction factor, the study demonstrates how strongly the ILI depends on underlying assumptions. The results show that low ILI values may result not only from low physical leakage, but also from structural system characteristics, uncertainty in the estimation of unavoidable annual real losses (UARL), and residual uncertainties in water balance inputs affecting current annual real losses (CARL). Across the dataset, correction approaches altered ILI values substantially (from −84% to +301%), highlighting the indicators’ sensitivity to pressure conditions, pipe material composition, burst rates, system configuration, and data quality. Given the European Union (EU) Drinking Water Directive and Taxonomy Regulation, this paper emphasises that the ILI requires contextual interpretation and reliable data. Findings indicate the ILI is valuable as a water loss management metric, but limited as a standalone benchmarking or regulatory performance indicator.