Water scarcity and the high energy demand of conventional desalination systems motivate the development of low-cost, low-carbon freshwater production technologies. Solar stills are attractive for remote and arid regions, but their productivity and efficiency are typically low. This work experimentally investigates a modified hemispherical solar still (MHSS) that integrates a parabolic dish collector, a hanging wick, a copper oxide nanofluid, a back reflector, and an external condenser. It evaluates its performance from a comprehensive 4E perspective (energy, exergy, economic, and environmental). Two identical hemispherical stills were constructed and tested under the climate of Kafr El-Sheikh, Egypt: a conventional hemispherical solar still (CHSS) and four MHSS configurations. The cases considered were: (1) dish-fed HSS with hanging wick, (2) case 1 plus CuO nanofluid, (3) case 2 plus back reflector, and (4) case 3 plus external condenser. Results show that the fully integrated system (case 4) increases daily freshwater productivity from 3.36 to 11.03 L/m2 compared with the CHSS, while the cumulative energy efficiency rises from about 31% to 66.35% and the exergy efficiency from about 1.8% to 5.92%. The annual freshwater yield increases from 1130 to 3752 L/year, reducing the specific water production cost from 0.0148 to 0.0099 $/L relative to the conventional still. From an environmental standpoint, the modified system avoids approximately 3.96 tons of COQ emissions over its lifetime compared with the CHSS. Overall, the proposed configuration substantially enhances thermal performance, water productivity, and economic and environmental indicators, demonstrating its potential as a sustainable option for solar desalination.