To overcome the deficiencies of the existing water quality indices, a re-designed quality index based on the Canadian Drinking Water Quality Index was developed as “Modified Water Quality Index” (MWQI) and applied for evaluating the groundwater quality in the drinking water sources of Bommanahalli area in Bangalore. The main modification that was made while developing the MWQI was allocating appropriate weight factors for the critical water quality input parameters. In the process of developing the revised/modified index, 30 groundwater samples were identified in the study area, 10 quality parameters, and the corresponding Bureau of Indian standards with respect to permissible drinking standards for water quality were chosen as the input quality parameters and corresponding benchmarks. This study was carried out both during the pre- and post-monsoon seasons of 2018. The results of the quality analysis interpreted that MWQI in the groundwater resources was 39.71 and 39.10, respectively, in the pre- and post-monsoon seasons. Based on the quality rank, the water quality scenario, is seen to be poor. As per MWQI value, 93.33% of the groundwater samples violate the quality index norms, that is, exceed the prescribed permissible values, failing the test. This study clearly illustrated that the MWQI explained the complete picture of water quality in a simple and extremely reliable manner and hence shows enormous promise for its application and large suitability across the globe.