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Despite high annual rainfall, Malaysia continues to face challenges in water quality and sustainable usage. Rainwater in urban areas is often acidic due to atmospheric pollutants. Thus, this study presents the development and evaluation of a residential rainwater harvesting and filtration system. Two collector models—Model A and Model B—were constructed to assess collection efficiency. Model B, designed with an integrated drainage system, collected 150 cm³ of rainwater in a shorter time, outperforming Model A. To address rainwater acidity, six filtration systems were tested using various ratios of activated carbon and limestone. Water quality parameters, including pH, conductivity, and Total Dissolved Solids (TDS), were measured before and after filtration. Initial pH values of collected rainwater ranged from 4.06 to 4.31, confirming its acidic nature. All filtration systems improved pH, with limestone-containing filters demonstrating the most significant changes. The 50:50 combination of activated carbon and limestone (Set 4) was the most effective, raising the pH to a near-neutral level of 7.11 and producing water with a TDS of 136 ppm. Although both conductivity and TDS increased slightly after filtration, all values remained within safe and acceptable limits, improving mineral content and water taste. The system was further tested under real-world conditions in Taman Nilam, Pontian, Johor. Filtered rainwater in this setting showed a pH increase from 6.33 to 7.74, with conductivity and TDS staying below recommended thresholds. These results confirm the system’s effectiveness in reducing rainwater acidity while ensuring water remains safe and palatable for household use. This study demonstrates that a rainwater harvesting system with a balanced filtration mix of activated carbon and limestone offers a sustainable, efficient, and practical solution for improving residential water quality in urban environments.