AbstractIn water distribution systems (WDS) of developing countries, data about assets and consumption have great uncertainty. That uncertainty propagates to the performance indicators (PIs), leading to possible incorrect management decisions. To reduce the PI's uncertainty, it is necessary to analyze and reduce errors of each input variable. This paper presents methodology, based on a set of activities, to reduce the uncertainty of water balance components and Infrastructure Leakage Index. The method is tested on the WDS of Požarevac (Serbia) city. The example demonstrates how execution of activities reduced the indicator's uncertainty, although the overall indicator's value wasn’t continuously improving.