We’re pleased to highlight this publication which investigates the reliability of using radon-222 (²²²Rn) as a tracer for groundwater age in alluvial aquifers. Accurate estimations of groundwater residence time (GRT)—the time since water infiltrated from the surface—are critical for effective water resource management, especially in systems that rely on bank filtration near rivers for drinking water supply. While ²²²Rn has long been employed as a natural tracer due to its radioactive decay properties and elevated concentrations in groundwater, most traditional models assume spatially uniform ²²²Rn production and purely advective flow— assumptions that rarely hold in real-world aquifers.