Integrated hydrochemical evaluation, quality assessment, mineral speciation, and irrigation suitability of surface waters in Ondo City, Southwestern Nigeria

Access to safe water is essential for public health, agriculture, and sustainable development. This study is carried out to garner information on the hydrochemical characteristics of surface waters in Ondo City, Southwest Nigeria, which have not been investigated. In this study, twenty surfacewater samples were collected and analyzed to determine physicochemical quality, and dominant hydrochemical processes. Standard analytical methods were used, while geochemical processes were interpreted through statistical tools and hydrochemical plots. Saturation indices were modeled using PH Redox EQuilibrium Code (PHREEQC) software. Results showed that pH (6.9–7.6) and temperature (29–33 °C) are within permissible limits. Electrical conductivity (152–2902 µS/cm) and total dissolved solids (77–1446 mg/L) indicated that most waters are excellent to good. Average concentrations (mg/l) of major ions, including: calcium, magnesium, sodium, potassium, chloride, sulphate, bicarbonate, and nitrate are 44.94, 17.21, 13.47, 8.68, 42.06, 22.00, 169.00, and 4.46 respectively were below World Health Organization guideline values. Correlation analysis revealed strong associations between parameters, suggesting contributions from both natural geological sources and human activities. Piper plots showed that most samples belong to the Ca–Mg–HCO₃ water type, reflecting recent recharge and carbonate weathering. Despite favorable chemical characteristics, the Water Quality Index revealed that about 90% of samples are poor and unsuitable for drinking. In contrast, irrigation indices showed that over 90% of the samples are suitable for agricultural use.