Hydrogeochemical characterisation and evaluation of groundwater suitability for domestic and agricultural use in the Ugumany watershed, Omo-Gibe Basin, Ethiopia

Groundwater is a crucial freshwater resource for domestic and agricultural use in Ethiopia’s semi-arid regions, but limited baseline hydrogeochemical data impede effective quality assessment, sustainable management, and public health protection. This study presents a comprehensive hydrogeochemical assessment of groundwater in the Ugumany watershed, Omo-Gibe Basin, Ethiopia, to determine its suitability for drinking and irrigation. Ten groundwater samples from springs, hand-dug wells, and pump wells were collected during the dry and wet seasons (2023–2024) and analysed for major ions and physicochemical parameters. Hydrochemical facies and controlling geochemical processes were evaluated using Piper and Gibbs diagrams, while irrigation suitability was assessed using SAR, RSC, MAR, RSBC, SSP, Kelly’s Index, and the Irrigation Water Quality Index (IWQI). The results showed seasonal fluctuations in water chemistry, with higher TDS (up to 405 mg/L) and turbidity (up to 80 NTU) during the wet season due to enhanced mineral dissolution and runoff. Fluoride exceeded the WHO limit (1.5 mg/L) in 30% of samples, with a maximum concentration of 2.65 mg/L and indicating localised health risks. Gibbs diagrams show rock–water interaction as the dominant control on groundwater chemistry. Most irrigation indices indicate suitable groundwater for irrigation; however, elevated RSC (>13 meq/L) and MAR (>80%) in some dry-season samples suggest localised soil sodicity and salinisation risks under prolonged irrigation. Groundwater in the Ugumany watershed is generally fit for domestic and irrigation purposes, although fluoride enrichment and seasonal salinity-related risks require targeted monitoring, protection of shallow sources, and appropriate fluoride mitigation strategies to ensure sustainable water use.