This study aims to assess the quality of storm sewer water in Ramadi city before its discharge into the Euphrates River and Al-Warrar Canal. Several samples were taken from the storm sewer in two different periods October and April months. Samples were tested in laboratories which included (PH), electrical conductivity (EC), alkalinity (Alk), total hardness (T.H), calcium (Ca), biological oxygen requirements (BOD5), chemical oxygen requirements (COD), nitrate (NO3). sulfate (SO4) dissolved solids (TDS), suspended solids (TSS), and some heavy metals such as copper (Cu) and zinc (Zn). In this study, the authors suggested a new approach for calibrating WQI values using the multiple linear regression (MLR) model and coefficients analysis The results showed that the (MLR) model is acceptable, the multiple linear regression analysis (MLP) was applicable to calibrate WQI values, and new WQI equation with four variables was developed (SO4, BOD5, TSS and TDS), The results showed that the MLR model has a coefficient of R2 equal to (0.859), which indicates that 85.9% of the variance of the data was explained as well as obtaining significance values greater than 0.05 for each of the absolute WQI value. According to analysis, SO4 is the parameter that has the greatest effect on WQI.