Abstract: This research is based on finding the way to minimize water utility in the petrochemical and petroleum industries due to high rate of water consumption. One of the petroleum refineries in the center of Iran has been considered as a case study. In this research, two key contaminants including Suspended Solid (SS) and Hardness (H) have been considered to analyze the water network. These key contaminants once were analyzed separately as a single contaminant and the amount of required fresh water was calculated for both of them. In this stage, amount of freshwater was reduced about 60.9 m3 h-1 (17%) and 203 m3 h-1 (59.7%) in terms of Suspended Solids (SS) and Hardness (H), respectively. As it is seen, water minimization within three optional operations for SS is less than H. Therefore, this contaminant is a limiting contaminant and can be selected as a key contaminant. In the next stage, two mentioned contaminants were analyzed simultaneously based on their mass transfer. The results show that the amount of required water is reduced from 340 to 197.26 m3 h-1 that is about 42%. Analyzing both methods show that amount of required water can be determined by mass transfer of suspended solids. In addition, the method based on multiple contaminants gives more precise results rather than single contaminant. Therefore, it is suggested that more contaminants and operations are considered to study water networks and reach water utility optimization based on key contaminant as well.