Impact of Rural Settlements on Groundwater Quality in the Semiarid Pishin Basin, Balochistan, Pakistan

Background and Objective: Groundwater is the main water source in the semiarid Pishin Basin, supporting drinking and agriculture. However, rural settlements with poor sanitation and waste management are increasingly degrading its quality. This study evaluates the hydrochemical characteristics and controlling mechanisms of groundwater in the Pishin Basin, a semi-arid alluvial aquifer system. Materials and Methods: Groundwater and agricultural soil samples were collected from the semiarid Pishin Basin, Pakistan, during October-November 2024. Physicochemical parameters, including major cations and anions, were analyzed using standard analytical methods in the Department of Geology, University of Karachi. All analyses were performed in triplicate with appropriate quality control and standardization procedures. Descriptive statistical analysis was conducted using SPSS 2022, and the obtained results were compared with WHO 2011 drinking water guidelines. Results: Groundwater is neutral to slightly alkaline (pH 7.4-8.0) and moderately warm (24.5-28.8°C), reflecting shallow circulation under semi-arid conditions. Total dissolved solids (177-2200 mg/L; mean 1032 mg/L) and hardness (340-1000 mg/L) indicate fresh to slightly saline water, with some samples exceeding WHO limits. The cation chemistry is dominated by Ca²⁺ and Mg²⁺ from carbonate weathering, while Na⁺ over Cl^– suggests silicate weathering and ion exchange. Bicarbonate is the main anion, with sulphate from gypsum and anhydrite dissolution. Elevated nitrate and potassium in selected locations indicate minor anthropogenic influence from fertilizers and organic waste. Conclusion: Groundwater chemistry in the Pishin Basin is primarily controlled by natural geochemical processes, including carbonate and silicate weathering, ion exchange reactions, and evaporation under semi-arid conditions, with minor anthropogenic impacts. While most parameters are within acceptable limits, localized exceedances of TDS, hardness, potassium, and nitrate highlight the need for continuous groundwater monitoring to ensure sustainable water quality management.