Optimizing Reclaimed Water Allocation for Sustainable Crop Diversification and Agricultural Productivity in Water-Scarce Regions: Iraq as a Case Study

Extended drought and growing water scarcity have severely impacted agricultural productivity across many regions in Iraq. Reclaimed water (RW) presents a sustainable alternative to conventional freshwater sources. Beyond easing pressure on diminishing water supplies, RW can restore underutilized farmland and reduce environmental damage from the discharge of inadequately treated wastewater. This study develops an agricultural RW distribution optimization model aimed at maximizing individual farm net benefits by efficiently allocating RW to a variety of crops. The model evaluates the allocation of two reclaimed water types: RW A (tertiary-treated) and RW B (secondary-treated), under five irrigation efficiency (IE) levels ranging from 45% to 85%. Formulated as a mixed-integer nonlinear programming problem, the model considers 14 different crops, allowing up to four crops per farm across a network of 84 farms. Results show that RW B consistently provides higher total and per-hectare net benefits than RW A when equivalent water volumes and efficiencies are applied. This advantage is mainly due to RW B ’s lower treatment cost, which allows for more economically efficient crop combinations. Increasing IE yields substantial gains in net benefit and supports crop diversity, with minor improvements (i.e., 45% to 55%) generating individual farm benefit increases exceeding 25%. While the total cultivated area generally increases with water availability and IE, nonlinear trends reveal the model’s preference for maximizing economic return through selective crop allocation rather than maximizing land use. Overall, the model demonstrates that reclaimed water, especially RW B , can serve as a cost-effective and sustainable solution for irrigated agriculture near urban centers. The flexible framework supports strategic decision-making and is transferable to other arid and semiarid regions facing similar water constraints.