Integrated hydrogeochemical assessment and groundwater quality mapping for irrigation suitability and health risk in Kandahar City, Afghanistan

This study evaluates groundwater quality in Kandahar City, Afghanistan, integrating hydrogeochemical characterization with water quality index (WQI), irrigation suitability assessment, and health risk zoning approaches. Groundwater is a critical drinking-water and irrigation resource in hard-rock aquifers, where quality is governed by complex rock-water interactions and can vary markedly across space. This study integrates hydrogeochemical characterization with a decision-oriented water-quality assessment to evaluate groundwater suitability for domestic consumption and agricultural use. Eighty groundwater samples were analyzed, and drinking-water quality was quantified using a Water Quality Index (WQI), complemented by irrigation hazard diagnostics including sodium percentage (Na%), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), permeability index (PI), Kelly's ratio (KR), and magnesium adsorption ratio (MAR). Spatial heterogeneity in groundwater quality was mapped using two interpolation approaches-Inverse Distance Weighting (IDW) and Ordinary Kriging-to contrast localized versus regional patterns and to identify priority zones for intervention. WQI classification indicates that most samples fall within the Excellent (38.75%) and Good (32.5%) categories, whereas 28.75% of samples are Poor to Undrinkable (15% Poor, 6.25% Very Poor, and 7.5% Undrinkable), highlighting discrete hotspots of degraded quality. Irrigation suitability is generally favorable, with uniformly low SAR (0-6.24; mean 0.91) and KR < 1 for all samples, while localized constraints are indicated by PI and MAR, and by elevated RSC in a subset of samples. A WHO-guideline exceedance-based health risk screening indicates that key concerns are associated with elevated total hardness (48.33% exceedance) and elevated chloride and TDS (40% each), with additional exceedances observed for sulphate (38.33%). Collectively, the findings demonstrate that coupling hydrogeochemical interpretation with WQI-based classification, irrigation indices, and geostatistical mapping provides an actionable framework for prioritizing treatment in high-risk zones, guiding safe allocation of sources for drinking, and sustaining agricultural water use through targeted management measures.