Assessment of Groundwater Hydrochemistry and Suitability for Drinking and Irrigation in Bauchi State

Groundwater is the principal source of drinking water and irrigation supply in Bauchi State, North East Nigeria, yet its hydrochemical characteristics, which determine suitability for different uses, are poorly documented across many of the state's local government areas. This study assessed the hydrochemistry of groundwater from forty-eight boreholes and hand-dug wells distributed across six local government areas in Bauchi State. Water samples were analysed for nineteen chemical parameters including major cations, major anions, trace elements, and derived hydrochemical indices. Hydrochemical facies were classified using Piper trilinear and Schoeller diagrams. Water suitability for drinking was evaluated against WHO 2022 guidelines, and suitability for irrigation was assessed using sodium adsorption ratio, sodium percentage, Wilcox classification, and residual sodium carbonate. Bicarbonate-calcium-magnesium type was the dominant hydrochemical facies, indicating carbonate weathering as the primary geochemical control. Fluoride exceeded 1.5 mg/L in 23 percent of samples from granitic terrain zones. Nitrate exceeded 50 mg/L in 18 percent of samples, predominantly near settled areas. Manganese exceeded 0.4 mg/L in 15 percent of samples. Sodium adsorption ratios were below 10 in all samples, indicating low sodicity risk for irrigation. Thirty-one percent of samples were unsuitable for drinking based on fluoride, nitrate, or manganese exceedances. These findings provide an evidence base for water source selection and treatment design in Bauchi State and recommend targeted fluoride mapping and community-level defluoridation interventions.

Keywords: groundwater hydrochemistry, Piper diagram, fluoride, irrigation suitability, Bauchi State