AbstractLeakage has become a crucial issue that needs to be addressed effectively by water suppliers in terms of economic management of water systems. A target setting method based on the ELL (Economic Level of Leakage) calculation is proposed in this paper. The methodology applied is developed specifically for the South Korean context to select a minimum achievable level of NRW (Non-Revenue Water) and verify the appropriateness of the current target within existing financial constraints by using limited available data. This approach is focused on the derivation of the NRW control cost curve by using the newly developed cumulative method that minimizes data fluctuation and enhances the cost curve reliability. This has been applied to a case study by using data collected from the water supplier information system. The results obtained in this case study show significant outcomes in respect of both identification of an economically optimal target and prevention of unnecessary investment to meet this aim. This advance in leakage management allows water suppliers to select a rational target and manage their system economically and efficiently.