Drought stress is a major constraint in eggplant cultivation, limiting growth, physiological performance and yield. Solanum relatives may provide alleles for improving drought tolerance. The objective of this study was to evaluate the responses of cultivated, wild and interspecific eggplant genotypes under water stress to identify drought-tolerant genotypes. Four-week-old plants of three Greek eggplant cultivars—S. macrocarpon (cultivated), S. dasyphyllum (wild), and three S. melongena × S. dasyphyllum hybrids—were grown under full and deficit irrigation and assessed for 10 agronomic and 7 physiological traits. Genotype, irrigation level and their interaction significantly affected most traits. Eggplant showed greater sensitivity under water stress with reductions in 9 agronomical traits, such as leaf number (12.9–15.8%), plant height (15.4–25.1%), LAI (47.7–55.4%), root (32.1–46.6%) and plant biomass (31.4–38.6%). S. dasyphyllum and S. macrocarpon maintained relative growth and physiological stability through different mechanisms, indicating enhanced drought tolerance. S. dasyphyllum exhibited reduction only in leaf number (11.5%), plant height (17.8) and LAI (23.9%), while S. macrocarpon exhibited reduction only in leaf length (18.1%) and LAI (55.0%). Interspecific hybrids displayed intermediate responses and heterosis under control (−22.2 to 66.6%) and stress (−29.8 to 81.5%) conditions. These findings support the use of wild or cultivated germplasm in breeding drought-resilient eggplant cultivars and rootstocks and enhancing crop sustainability.