The objectives of this study are to analyze the underground water quality of Bommanahalli zone by water quality index. Eleven physico-chemical parameters such as pH, Electrical Conductivity Calcium, Magnesium, Chloride, Sulphate, Total Hardness, Fluoride, Nitrate, Total Dissolved Solids, Iron and Alkalinity collected from 10 different locations in a pre-monsoon period of 2017. In this study 90% water samples were found poor quality and only 10% water samples falls under moderately good category. The water quality index ranges from 39.03to 453.90. Therefore there is a need of some treatment before usage and also required to protect that area from contamination.