The International Water Association and the American Water Works Association have developed the concept of water audit to prevent water loss and identify the factors that cause it. In Türkiye, the water and sewerage administrations of the cities are requested to prepare the "standard water balance table (SSDT)" to combat water losses and provide common terminology in water control. The main objectives of this study are to reveal the contribution of a sustainable water future through water auditing, to determine the loss of income due to the amount of non-revenue water (NRW), to calculate the opportunity cost, and to propose the "opportunity cost as a model" for calculating the NRW cost. As a result, we believe that the calculation of the opportunity cost of NRW will reduce the estimated cost of NRW and contribute to the loss management calculations.