Northwest Tunisia is facing increasing pressure from overexploitation and human activities, resulting in serious groundwater quality issues, particularly salinization and nitrate pollution. This study aims to evaluate the spatial and seasonal variations in the hydrochemical characteristics of the Bulla Regia aquifer, assessing its suitability for both drinking and irrigation purposes. A total of 12 boreholes were sampled during both dry and wet seasons. Two indices were used to evaluate water quality: The Irrigation Water Quality Index (IWQI) and the Drinking Water Quality Index (DWQI). IWQI was calculated using parameters such as sodium percentage (Na%), electrical conductivity (EC), sodium adsorption ratio (SAR), magnesium hazard (MH), permeability index (PI), Kelly's ratio (KR), and soluble sodium percent (SSP). DWQI included measurements of pH, total dissolved solids (TDS), calcium, magnesium, sodium, chloride, sulfate, potassium, bicarbonate, and nitrate. The spatial distribution of groundwater quality parameters was mapped using GIS tools. The IWQI results showed that all samples from both seasons were classified as having a "Severe Restriction" for irrigation use. Regarding drinking water, DWQI results indicated that 27.17% of samples in the wet season and 25% in the dry season were rated as "poor", "very poor", or "unsuitable" for human consumption. These findings highlight a significant decline in water quality, rendering the groundwater largely unsuitable for irrigation, except for salt-tolerant crops, and unsafe for drinking. The degradation is due to both natural and human-induced factors. Our study can serve as a foundational database for informed planning, management, and protection of groundwater resources, and provide an overview for decision-making authorities in Tunisia and other arid regions to take necessary measures to improve water quality.Graphical AbstractThis graphical abstract presents a comprehensive visual overview of a study assessing the spatiotemporal suitability of groundwater for drinking and irrigation in Bulla Regia, Northwestern Tunisia, employing a GIS-based approach. The study integrates hydrochemical analyses and water quality indices, specifically the Drinking Water Quality Index (DWQI) and the Irrigation Water Quality Index (IWQI), to assess groundwater degradation driven by geogenic and anthropogenic influences. Organized into four main sections -Introduction, Methodology, Key Findings, and Conclusions - the graphical abstract ensures a logical flow of information. The study begins with a geographic contextualization of the study area and a simplified flowchart outlining the hydrochemical methodology employed. The central section highlights key findings, showing that most groundwater samples exceeded WHO limits for salinity-related parameters (Na+, Cl-), mainly due to halite dissolution. Visual comparisons between wet and dry seasons illustrate the seasonal variation in groundwater quality, revealing that only 9% of samples met potable standards in the dry season, compared to 25% in the wet season. For irrigation, all areas were under "Severe Restriction" as per the IWQI. The conclusion underscores the urgent need for sustainable groundwater management and the adoption of climate-smart agricultural practices in the studied region. Using consistent fonts and professional color palettes enhances readability, while including recommendation panels encourages policy-level action.