Freshwater scarcity continues to intensify the need for low-cost, sustainable desalination technologies. Passive solar stills offer a simple, renewable solution, but their practical use is limited by low productivity due to weak heat transfer in the basin water. This study experimentally investigates the use of an Al2O3-CuO hybrid nanofluid to improve the performance of a conventional single-slope solar still. Four systems were fabricated and tested: a conventional solar still without a hybrid nanofluid (SS1), and three modified solar stills containing 0.1 wt.% (SS2), 0.2 wt.% (SS3), and 0.3 wt.% (SS4) Al2O3-CuO hybrid nanofluid in the basin water. The systems were evaluated in terms of distillate yield, heat-transfer behavior, energy, exergy, economic, environmental, exergo-economic, enviro-economic, life-cycle conversion efficiency (LCCE), and sustainability performance. The results indicate that SS4 achieved the highest thermal efficiency of 48.1%, followed by SS3 (44.1%), SS2 (41.9%), and SS1 (38%). Similarly, exergy efficiency improved across the configurations, with values of 6.23% for SS1, 7.8% for SS2, 7.93% for SS3, and 8.1% for SS4. Over its lifetime, configuration SS4 demonstrated 28% greater CO2 mitigation than the SS1 system, along with a minimum energy payback time of 1.34 years (energy basis) and 16.1 years (exergy basis). SS4 also showed the highest lifetime CO2 mitigation of 8.872 tons, a carbon credit gain of 120.28 $, an energy-based life-cycle conversion efficiency of 9.24%, and a sustainability index improvement of 2.6% compared with SS1. Overall, the results indicate that 0.3 wt.% Al2O3-CuO hybrid nanofluid is the best-performing concentration within the tested range and can significantly improve the thermodynamic, economic, environmental, and sustainability performance of passive solar stills.