User-friendly tool for the assessment of groundwater contamination risks by long-term irrigation with reclaimed water

Using reclaimed water for crop irrigation is a vital practice to reduce water consumption, but introduces contaminants into soils that may leach to groundwater. Consequently, decision-makers worldwide must assess groundwater contamination risks under a range of site-specific conditions. We present a process-based and user-friendly prediction tool to assess long-term groundwater contamination risk from irrigation with micropollutant-containing waters. The tool condenses outputs from numerical simulations into a simplified Excel interface. A total of 6160 simulations were performed using Hydrus-1D to model coupled water and solute transport in a 2 m soil profile over 50 years. Hydrus-1D has become a standard tool for simulating water and solute fluxes in the vadose zone. Simulations covered 40 combinations of site-specific conditions, including five soil texture classes, two climate regimes (humid and semi-arid), two irrigation strategies (demand-based and all-season), and two plant uptake scenarios (none or passive). For each condition, 154 combinations of sorption coefficients (K _d ) and microbial degradation half-lives () were evaluated. Leaching percentages were fitted as a functions of log₁₀-transformed K _d and values using a parametric Fourier cosine series, which reproduced simulated outcomes with RMSE < 0.4%. The tool allows for initial, site-adaptable screening of groundwater contamination risks for substances whose fate in soils is sufficiently described by linear sorption and first‑order biodegradation. Practical use requires the selection of site scenarios and reaction parameters; we therefore provide guidance and literature anchors for parameterization and further discuss limitations of the tool (e.g., homogeneous profiles, fixed 2 m depth, free drainage, non-representation of preferential flow).