Hydrogeochemical and water quality study of Lower Bilate River Catchment, Southern Rift Valley of Ethiopia

The study area is located in Ethiopia's Main Rift Valley, where surface and groundwater are the primary sources for household and agricultural needs. The study aims to investigate the hydrochemistry and water quality of the area using graphical, multivariate, and Water Quality Index (WQI). The result shows that the order of the principal cation and anion distributions is Na⁺  > Ca²⁺  > K⁺  > Mg²⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > F⁻ > NO₃⁻, NH₄⁺, respectively. The primary water type is Na-HCO₃, which demonstrates the hydrolysis of sodium-rich silicate minerals and the evolution of groundwater. The WQI revealed that very poor water (34.2%) comprised most of the samples and was distributed throughout the study region. Following this, good water quality accounted for 21.05%, poor water quality also accounted for 21.05%, and excellent water quality represented 15.77% of the samples. The study's findings indicate that fluoride concentration, with an average value of 8.09 mg/l, is the main contributor to the region's poor drinking water quality. The problem with water quality worsens as it approaches the outlet of the catchment. In terms of irrigation water quality, the Sodium Absorption Ratio (SAR) demonstrates that surface water (Rivers) samples (average SAR value = 2.57) were very acceptable for irrigation to groundwater with an average SAR value of 22.4. The entire surface water sample's (rivers) sodium hazard vs. salinity hazard falls into category C1-S1, and both the electrical conductivity and sodium hazard index are quite low, making it appropriate for irrigation. The study findings will assist government agencies and water management authorities in safeguarding the local population against issues related to water quality.