To obtain an optimum irrigation management strategy, reaching lower water applications as well as highest possible yields, can be complex regarding various plant and environmental parameters along with various dominancy of each parameter. For this purpose, the relationship among the input irrigation factors (irrigation interval, water salinity, environment), moderate factors (evapotranspiration, soil salinity, plant parameters, fruit parameters, crop yield) and a response (WUE: water use efficiency) were carefully determined using a structural equation modeling according to the first year of experiments. The relations were improved using the dataset of the second year of experiments. The improved models were then used in two optimization methods, water cycle algorithm (WCA) and genetic algorithm (GA), to determine the best combination of irrigation factors and optimize eggplant cultivation. The structural equation modeling indicated that the irrigation interval negatively impacted WUE with a more dominant effect on plant parameters, while water salinity negatively impacted the WUE with a more dominant effect on soil salinity, crop yield and fruit parameters. Further, a low salinity level will be more important than full irrigation to optimize WUE. WCA appeared that the optimal ranges of irrigation interval and water salinity were 2.13‒5.23 day and 0.8‒2.21 ds/m cultivated in outdoor cultivation, resulting to optimize evapotranspiration, soil salinity, fruit parameters and crop yield in the ranges of 346.23‒738.19 mm, 4.16‒9.45 ds/m, 33.81‒35.12 cm and 1715.7‒2190.8 g/plant, respectively; and thus, increase WUE in the range of 3.08‒4.89 g/(plant-mm). WCA and GA presented very close optimal values.