Access to safe and clean drinking water remains a critical public health issue in Karachi, where water quality from both groundwater sources and treated supplies varies widely. This study presents a comprehensive comparative analysis of 172 water samples collected from various locations across the city, including 119 samples from RO treatment plants and 53 from bore wells. The samples were tested for essential physicochemical parameters such as pH, TDS, turbidity, electrical conductivity, TSS, chloride, and hardness, which are vital indicators of water safety and potability. Using the WQI method, the results showed that a significant portion of bore water approximately 68% was unsuitable for drinking due to high levels of dissolved salts, microbial contamination, or other pollutants, whereas over 91% of the RO-treated water samples were classified as having excellent or good quality. Interestingly, the analysis also revealed no significant correlation between the cost of RO water and its quality, indicating that higher prices do not necessarily guarantee safer or better-quality water. These findings highlight the effectiveness of RO systems in improving water safety but also emphasize the need for consistent monitoring, proper maintenance, and regulatory oversight to ensure ongoing water quality. Ultimately, the study underscores the importance of public awareness and policy interventions to provide affordable, safe drinking water for Karachi’s growing population and dispels the misconception that higher treatment costs automatically equate to better water quality.