The rising demand for water and the depletion of natural water resources, as well as the current environmental problems, have led to the need for the provision of additional quantities of water to enhance water resources and the sustainability of ecosystems. Water harvesting technologies are one of the most effective solutions to treat this issue. In this study, appropriate zones for rainwater harvesting in the Diyala Watershed were identified using the Geographic Information Systems-based multi-criteria analysis and fuzzy logic model. Seven criteria were selected: slope, stream order, rainfall, runoff, hydrological soil group, land use, and distance to roads. The map of suitability was categorized into five categories, ranging from very low to very high, and the map showed that the majority of high-suitability areas are situated in the southeast parts of the study area, while most of the regions of low suitability are located in the western and northern parts. Lastly, this study will contribute to the effective planning and administration of rainwater on a broader scale.