Development and application of a scalable multi-barrier framework for risk management in agricultural water reuse under the EU regulation

In the European Union, treated wastewater (TWW) is increasingly used to supplement agricultural irrigation. Implementation is governed by site-specific Risk Management Plans (RMPs) mandated by Regulation (EU) 2020/741, which require a risk-based approach to TWW reuse. A central instrument for managing microbiological risk is the multi-barrier approach. However, its application is hindered by heterogeneous crop–irrigation configurations and the lack of a unified operational method in existing guidance. Here, we present a rule-based attribution matrix that operationalises the multi-barrier approach using routinely available, georeferenced datasets. The matrix links crop use categories, edible-part height, irrigation methods, TWW quality classes at the wastewater treatment plant (WWTP) outlet, as well as accredited barriers to generate auditable field-level prescriptions (direct reuse, conditional reuse with a quantified number of barriers, or prohibition) and indicators at the level of individual irrigation districts. The method was applied through two complementary applications: (i) at water reuse system level in an irrigation district RMP to produce multi-year, plot-specific prescriptions; and (ii) a multi-irrigation district application, in which the same methodology is replicated across multiple irrigation districts and the results are aggregated to derive irrigation scenarios under alternative barrier configurations and TWW classes at the WWTP outlet. Analysis showed that, at water reuse system level, the mean irrigable share of the cultivated area increased progressively with barriers (from 46% to 61% under class D effluent) and with improved TWW quality classes, reaching full eligibility under class B. At multi-district scale, class C effluent combined with three accredited barriers achieved complete irrigability across all ten irrigation districts. By providing the first rule-based methodology to translate Regulation EU 2020/741 into auditable, plot-level prescriptions, the study bridges regulation and practice: it supports site-specific microbiological risk management within RMPs at the water reuse system scale, generates planning-scale indicators at the irrigation district level, and offers a reproducible, data-lean framework whose rule-base logic is transferable to any jurisdiction aligned with the WHO health-based targets.