Water scarcity in arid and semi-arid regions increasingly stresses groundwater resources, compromising their availability and quality. In this context, desalinated seawater (DSW) represents a sustainable alternative when combined with conventional water sources and efficient irrigation systems. This study assessed the effect of three irrigation treatments on greenhouse-grown tomato crops in an open hydroponic system. The treatment T1 used only DSW, while T2 and T3 were mixtures of DSW and groundwater in different proportions to achieve electrical conductivities (EC) of 2.5 (T1), 3.5 (T2), and 5.5 dSm-1 (T3), respectively. Each treatment received the same fertilization level through fertigation, adjusted to the crop's nutritional needs. Experiments were conducted in duplicate in two greenhouse sectors (West and East). The data on yield, fruit quality, fertilizer use, and water consumption were analyzed. Results indicated that higher EC reduced marketable and total yield, decreased fertilizer use efficiency, and increased the combined cost of water and nutrients per unit of marketable fruit. Additionally, higher EC affected fruit weight and diameter, increased soluble solids, and altered dry matter content. These findings demonstrate that DSW can be an effective and environmentally sustainable irrigation strategy for greenhouse crops.