An integrated master plan to enhance agricultural water reuse at irrigation basin scale

In Mediterranean regions, irrigation demand is rising while conventional water resources are becoming less reliable due to recurrent droughts, competing uses, and environmental constraints. Treated urban wastewater (TWW) is therefore gaining increasing attention as an unconventional resource capable of supplementing conventional irrigation supplies and supporting climate-change adaptation strategies. However, moving from isolated pilot schemes to implementation across large irrigation basins is complex. Reuse at this scale isn't a single pipeline linking one wastewater treatment plant (WWTP) to one field. Instead, it's part of a large, distributed, dynamic irrigation system serving many agricultural fields with varied crops and methods. Numerous, dispersed WWTPs produce TWW of varying quality, and the irrigation network conveys and mixes flows under different conditions.

The key planning challenge is therefore to integrate TWW with conventional sources within a single allocation and operations framework that considers both water quantity and quality. Quantitatively, planners must synchronise TWW and conventional supplies by matching seasonal availability to spatially variable irrigation demand across multiple districts, often under pronounced temporal mismatches that make storage and operational regulation essential. Qualitatively, TWW may contain pathogens and chemical contaminants, requiring preventive risk management throughout conveyance, distribution, and on-farm application. In the European Union, Regulation (EU) 2020/741 formalises these requirements by mandating a site-specific Risk Management Plan (RMP) and defining four reclaimed-water quality classes (A–D) linked to minimum quality standards and intended agricultural uses. Basin-scale planning must integrate volumetric allocation, infrastructure, and compliance considerations across diverse crop–irrigation setups with varying quality-class requirements. Current assessments often treat TWW as isolated; a unified framework combining these aspects is missing.

This study presents a novel, EU-aligned comprehensive methodology to assess and optimise the potential for agricultural reuse of treated wastewater in large, multi-district irrigation basins. The approach is designed to be generally applicable and adaptable to specific case studies, using routinely available stakeholder datasets integrated within a GIS-enabled framework. The methodology comprises six interconnected phases: (i) identification and spatial characterisation of areas suitable for reuse; (ii) area-specific resource–demand water balances (available resources versus irrigation requirements); (iii) assessment of current WWTP effluent quality according to Regulation (EU) 2020/741; (iv) determination of the reclaimed-water quality class required by currently irrigated surfaces based on crop type, irrigation method, and consumption mode; (v) definition of intervention scenarios to maximise reuse potential considering territorial and infrastructural constraints and irrigation needs; and (vi) identification of structural and operational measures prioritised over time to achieve sustainable, efficient, and EU-compliant outcomes.

The methodology was applied in Northern Italy within the Consorzio della Bonifica Renana (CBR) multi-district irrigation system, in collaboration with the local water utility (HERA). The application demonstrates how the framework transforms accessible information into decision-ready priorities, identifying candidate districts, WWTP clusters, and phased intervention portfolios and clarifies key barriers (infrastructure, storage, management, monitoring capacity, and quality-class constraints) while outlining actionable pathways to enable safe, Regulation (EU) 2020/741 compliant reuse at basin scale.