Assessment of the Physico-chemical Quality of Surface Water in the Bolo and Niouniourou Rivers for Drinking Water Supply in the City of Fresco, Côte d’Ivoire

Access to safe drinking water remains a critical challenge in coastal West African urban centers, particularly in resource-limited settings such as Fresco, Côte d'Ivoire. This study evaluates the potabilization potential of the Bolo and Niouniourou rivers to inform sustainable water supply strategies in hydrogeologically complex estuarine environments. Water samples were collected from 20 stations during the peak flood period (July 2025) and analyzed for 24 physico-chemical parameters. Results revealed contrasting hydrochemical patterns between the two rivers driven by differential hydrodynamic forcing. The Bolo River maintained a freshwater facies (mean conductivity: 1,141µS/cm; dissolved oxygen: 6.28mg/L) under fluvial dominance, where high flood discharge effectively repelled saltwater intrusion through hydraulic flushing mechanisms. Conversely, the Niouniourou River exhibited severe mineralization (conductivity: 3,308µS/cm; chlorides: 912mg/L), attributable to tidal inertia and saltwater trapping that persists despite elevated discharge during the monsoon season. Compliance assessment against WHO drinking water guidelines confirmed the Bolo River's suitability for conventional treatment pathways, whereas the Niouniourou River's chronic salinity burden renders it unsuitable for potabilization without prohibitively expensive desalination technologies. These findings underscore the fundamental importance of hydrodynamic forcing in governing coastal water resource quality and accessibility. The study demonstrates that site-specific hydrodynamic assessment is essential for evidence-based water supply planning in estuarine contexts.