Discharge of industrial water into the natural water sources is a point of concern in developing countries. Government sets the quality of discharge water based on the water bodies on which it is being discharged. A host of water quality indices, mostly for the drinking and ground water, are available to classify the water quality. The water quality indices for discharge water are also very important especially for the mining and mineral industries. Mine waters are found to be associated with pollutions like heavy metals, turbidity, alkalinity, acidity, dissolve solids, and other organic, non-organic pollutants. Thus, degree of mine water pollution is varying with the types of host rocks. As the Indian coal mines are free from sulfur, most of the coal mines do not envisage any threat of acid mine drainage as well as heavy metal pollution. Considering this, coal mines go for controlling of physical parameters of the discharged water and allowed its discharge on satisfactory testing result. It is, therefore, important to develop a water quality index to classify the mine water pollution level in a rationalize manner to decide the requirement of treatments, selection of types of discharge water bodies, etc. In this paper, some of the important and widely used water quality indices are reviewed and a newly developed water quality index for discharged mine water is highlighted. A new effluent water quality index (EWQI) is also proposed in this study for establishing quality index of three coal mines. This index incorporates 7 organoleptic, 16 undesirable and 10 toxic parameters for determining the quality index. A weighted-rating system is used for arriving at the index value. The sensitivity of each contaminant for degrading the discharge water quality is also analyzed. Application of EWQI in 3 coal mines reveals that despite the mine discharges satisfy physical properties in testing, EWQI identifies their unacceptance for discharging to natural water bodies except for Mine-3. This classification will also help the environmental apex bodies to understand the pollution levels and points of concern to be mitigated for each mines.