Water quality assessment is a major concern before using the water for domestic or industrial purpose. Researchers have developed different water quality indexes to measure and control the quality of surface and ground water. As water quality index is a useful and distinctive rating which summarizes the current state of water quality, the treatment proposal of the water can be proposed along with water quality assessment. Several national and international organizations have developed different water quality indexes for surface water quality assessment. Rating of some of those water quality indexes are conflicting in nature. This kind of conflict rating creates difficulties in quality assessment of surface water in a particular area. In this study, a multi-objective optimization model has been developed for water quality assessment in a mining area. Water quality parameters like pH, dissolved oxygen, biological oxygen demand, nitrate, total solids and turbidity have been considered as decision variables whereas three different water quality indexes Horton’s Water Quality Index (HWQI), National Sanitation Foundation Water Quality Index (NSFWQI) and Oregon Water Quality Index (OWQI) have been considered as model objectives. Minimum value of HWQI and maximum values of rest two water quality indexes are desirable to the quality manager. In this model, HWQI has been minimized and NSFWQI and OWQI have been maximized to assess the quality of surface water in a coal mining area in India. Pareto optimal fronts between two set of conflicting objectives represent quality ratings of the surface water. The compromised water quality index values of conflicting objectives help to choose the correct option for the utilization of water. Computational results indicate that the proposed multi-objective optimization model can be used as water quality assessment tool which is more efficient than any particular water quality index used by the researchers.