Assessment of Groundwater Quality for Drinking Purposes Using Water Quality Index (WQI) in Fianga Region, South-Western Chad

Abstract

Groundwater is an important source of water for domestic use in the town of Fianga, south-western Chad, but local information on its suitability for drinking remains limited. This study assessed groundwater quality using the Water Quality Index (WQI) approach and selected physicochemical parameters from 21 boreholes. The parameters considered were total dissolved solids, electrical conductivity, temperature, pH, Mg²⁺, Ca²⁺, K⁺, Na⁺, Cl⁻, HCO₃⁻, SO₄²⁻ and NO₃⁻. The results were compared with the drinking-water quality standards applied in the manuscript, and WQI values were calculated to classify the sampled boreholes. The borehole waters were generally acidic to neutral, and most measured parameters were within the recommended limits for drinking purposes. However, one borehole showed a nitrate concentration above the recommended threshold, indicating a possible localised influence of pollution. The WQI values ranged from 43.09 to 78.37. On the basis of the WQI classification, 57.14% of the sampled boreholes were classified as having excellent water quality, while 42.86% were classified as having good water quality. No borehole was classified as poor, very poor or unsuitable according to the WQI categories used in the study. These findings indicate that the groundwater sampled in Fianga is generally suitable for human consumption, although the borehole with elevated nitrate requires attention. The study provides baseline information for groundwater monitoring, planning and management in the area and highlights the need for continued assessment using a broader set of physicochemical parameters and a larger number of boreholes. The results can support local decision-making where groundwater is used for household supply.