<p>Groundwater quality assessment is a critical component of sustainable water resource management, particularly in coastal semi-arid regions where groundwater constitutes the primary source of supply. Despite numerous hydrochemical studies conducted worldwide, many have not fully addressed irrigation suitability in such vulnerable settings by integrating both geochemical processes and irrigation water quality indices. This study aims to evaluate the groundwater quality of the Aousaja-Ghar El Melh aquifer in northern Tunisia with a focus on its suitability for irrigation. A comprehensive hydrochemical approach was employed, combining major ion chemistry, facies classification, geochemical process identification, and multiple irrigation quality indices. Results reveal that most samples belong to the Ca-Mg-SO₄ facies, characterized by permanent hardness, while the remaining samples correspond to Na-Cl facies types. Groundwater chemistry is primarily governed by evaporation and water–rock interaction mechanisms: evaporite dissolution and reverse cation exchange. Irrigation Water Quality Index (IWQI) values are between 44.2 and 91.3, revealing that 58% of the samples belong to the moderate restriction class (suitable for medium and high permeability soils requiring moderate leaching for salt-tolerant crops), 34% to the low restriction (appropriate for light textured soils) and 3% to the high restriction class (not recommended for irrigation purposes). These findings are further supported by Wilcox and USSL diagrams, which highlight the predominance of acceptable irrigation water but also emphasize significant salinity hazards. The findings provide a robust and integrative evaluation of irrigation water quality, offering a valuable decision-support framework for sustainable groundwater management in semi-arid coastal aquifers.</p>