<p>Water resources are increasingly under pressure due to climate changes, recurring droughts, rising food demand, and increasing consumption from urban and industrial sectors. In response, seawater desalination systems have gained prominence as a potential solution. However, the negative environmental impacts of these systems raise significant concerns. Thus, the identification of environmentally optimal sites for desalination plants is critically important, particularly in the Sistan and Baluchestan Province as the case study. This study presents a framework that considers ecological and social factors, such as coral reef, seagrass beds, and nesting sites for the hawksbill sea turtle to address the optimal site selection for desalination power plants. The effect of expert judgment (weights) on the suitability of selected locations was investigated and compared to the case that taking into account the same weights. The key criteria was defined, and a GIS-based multi-criterion decision making (MCDM) was utilized. Various coastal, marine, and environmental factors were identified and overlaid to create a suitability map. The unweighted overlay showed different suitability patterns compared to the weighted overlay. The filed investigation was carried out to validate and ensure about the suitability of the proposed areas by overlaying. The field assessments confirmed that the weighted map aligned better with real-world observations, making it the final chosen map. It means moderately and highly suitable areas of this map which are the best areas to install desalination systems.</p>