This study investigates the hydrological processes driving groundwater recharge in the Avignon Plain (south‐eastern France) through a detailed analysis of the interactions between irrigation, rainfall and soil water using long‐term isotopic monitoring and lumped parameter modelling. More than 15 years of monthly isotopic data from rainwater, surface water, soil water and groundwater were analysed to quantify the contributions of gravity‐fed irrigation and natural rainfall to aquifer recharge. Our results show that gravity‐fed irrigation contributes about 85% of the recharge, highlighting the significant role of traditional agricultural practices in maintaining groundwater levels. Through isotopic tracing and modelling, we observed variations in transit times, with faster infiltration pathways associated with irrigation flows compared to more prolonged recharge from rainfall. This study not only demonstrates the effectiveness of isotopic techniques for assessing water sources in complex recharge scenarios but also provides insights into how irrigation practices affect groundwater sustainability. These results contribute to current thinking on sustainable water management and highlight the need for integrated approaches that reconcile agricultural water use efficiency and groundwater conservation.