<p>This study evaluated seasonal groundwater quality variations and suitability for drinking and irrigation during wet and dry seasons in Ubungo Municipality, Tanzania. Residents in Ubungo Municipality mainly depend on groundwater for domestic and irrigation use, but face challenges like poor quality, declining levels, seasonal variations, saltwater intrusion, and groundwater degradation. Water quality index (WQI), sodium adsorption ratio (SAR), sodium saturation percentage (SSP% %), magnesium hazard (MH) and permeability index (PI) were used to evaluate the suitability of water for drinking and irrigation purposes. Pearson correlation, Piper diagram, and multivariate analysis were used to assess groundwater and shallow well water quality. Findings indicated that groundwater in both wet and dry seasons is predominantly of the Na–Cl water type, with the wet season showing slight mixing with other hydrochemical facies, while the dry season exhibits a more pronounced and concentrated Na–Cl signature. In most cases, shallow wells had elevated concentrations of ions and microbes compared to boreholes. Boreholes which were suitable for drinking in wet and dry seasons were 34 and 92%, respectively, while all shallow wells were unsuitable for drinking during the wet season. Most of the groundwater sources were suitable for irrigation purposes in both seasons. The study recommends regular monitoring and treatment of water sources to ensure safe drinking water supply and sustainable irrigation practices in Ubungo Municipality.</p>