The primary goal of the study is to assess the performance of the existing potable Water Supply System (WSS) in the Sultanate of Oman using hydraulic simulation models and existing performance Indicators. Al Amerat Wilayat network has considered for the case study. The study aimed to help the decision-makers at Public Authority for Water (PAW) understand its distribution system needs and assist them in long-term planning of water assets. More specifically, the detailed objectives of the study are to evaluate the performance of the water supply system for the study area (Al Amerat Wilayat) by using a set of Performance Indicators. Besides, investigate the efficiency and hydraulic performance of Al Amerat Wilayat water distribution system using hydraulic simulation analysis and model. Finally, a survey made across public water system in Al Amerat to determine current water loss estimates, and then evaluated the financial impact posed by Non-Revenue Water (NRW) and how this impact could be minimized. The performance indicators selected from the International Water Association (IWA) indicators to evaluate Al Amerat WSS. Then, the methods of evaluating and scoring the performance indicators were developed. In order to determine the WSS efficiency, various data collected from PAW such as as-built information, Supervisory Control & Data Acquisition (SCADA) data and field data like actual flow, pressure. Subsequently, the model was built and calibrated using historical data collected from SCADA. Finally, American Water Works Association (AWWA) methodology and software were used for water audit and water losses estimate. The indicators exhibits the performance of WSS, total 37 indicators used. The results indicated that the system scored 95 out of 148, which means some of the indicators have scored very low and the operation team need to have an action plan in order to enhance the performance level. In terms of technical performance indices (TPIs), this evaluation tool is handy and presented that Al-Amerat WSS having expansion capacity for future demand. Presently 70% of water distribution network covered in Al-Amerat area, which shows that the network will undergo extensions as per the development takes place. The calculation indices that water age at WSS was more than three days but the chlorine decay level was within the acceptable standard. The calculation illustrated that NRW for Al-Amerat WSS in the year 2018 was 33% which is around 3.82 Million OMR. It is a huge sum, and the percentage is significantly high when compare with other developed countries for example; The Netherlands and Germany.