The development of drought-tolerant varieties is one of the most effective approaches to preventing yield and quality losses in agricultural production. Therefore, in this study, 20 Altınbaş melon inbred-line genotypes, 2 standard, and 2 hybrid varieties were evaluated in an open field test to investigate the changes in their leaf pigments, photosynthetic activity, and nutrient contents under full irrigation (I<inf>100</inf>) and 50% water stress (I<inf>50</inf>) conditions for 2 years (2023–2024). The results indicated an increase in leaf pigment contents and leaf temperature (T Leaf) but a decrease in stomatal conductance (gs) and actual photosystem II (PSII) efficiency under water stress. Moreover, the applied water stress significantly restricted the uptake of nutrients. The results of principal component analysis (PCA) revealed significant differences in chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoid (Car), iron (Fe), magnesium (Mg), and manganese (Mn) under the I<inf>50</inf> treatment. The evaluation of the genotypes found that genotype number 61 showed tolerance to water stress, while genotypes 5, 22, and 37 were sensitive. It is suggested that leaf pigments and some nutrient elements are the main criteria for identifying genotypes that are tolerant to water stress and provide significant insights into screening large gene pools.