The COVID-19 pandemic has generated an unprecedented surge in disposable face mask waste, with an estimated 3.4 billion masks discarded daily, exacerbating global plastic pollution while urban agriculture faces water scarcity challenges, particularly in arid regions. This study addresses both issues by developing a circular solution that repurposes surgical masks into hydrogel-enhanced growth substrates for water-efficient urban farming. Sterilized masks were shredded and blended with cross-linked cellulose hydrogels (15% v/v) to create a water-retentive medium, tested in rooftop gardens under arid conditions over 90 days using IoT-monitored irrigation. Results demonstrated a 42% reduction in water use compared to conventional soil, while maintaining 95% crop survival rates (vs. 68% in controls) and increasing tomato yields by 27% due to stable moisture retention. Each square meter of substrate recycled ~35 masks, preventing 1.2 kg CO₂e emission from incineration. The methodology aligns with ecological engineering principles, leveraging mask-derived polypropylene fibers as a structural base for hydrogels, which also reduced microplastic leakage by 89% compared to untreated mask waste. This approach not only diverts PPE from landfills but also enhances urban food security in water-stressed areas. This study concludes that scaling this innovation could mitigate pandemic-era plastic pollution while supporting SDGs 2 (Zero Hunger), 6 (Clean Water), and 12 (Responsible Consumption), with future research needed to optimize hydrogel formulations for diverse crops and climates.