Monitoring and assessment of groundwater suitability for drinking and irrigation in the granary region of central-west Bangladesh using entropy index

Introduction: This study assesses groundwater suitability for drinking and irrigation in central-west Bangladesh’s granary region. Using the entropy water quality index (EWQI) and conventional irrigation indices, it evaluates water quality essential for public health and sustainable agriculture. Materials and methods: Groundwater samples from multiple sites were analyzed for major physicochemical parameters. Drinking suitability was assessed using EWQI, while irrigation suitability was evaluated through USSL, Wilcox, and Doneen indices. Hydrochemical facies and geochemical processes were interpreted using Piper, Gibbs, and bivariate analyses. Results and discussion: Groundwater in the study area is neutral to alkaline in nature and is dominated by calcium (Ca2+) and bicarbonate (HCO3-), characterizing a Ca-Mg-HCO3 water type. This composition reflects calcite dissolution and ion-exchange processes. Gibbs plots and bivariate relationships indicate that rock weathering, particularly of calcite, dolomite, and silicate minerals, largely governs the groundwater chemistry. The EWQI and WQI results reveal that 96.67 % of the samples are unsuitable for drinking, with 76.67 % classified as poor quality. PCA results indicate that the dissolved constituents are primarily of geogenic origin, with minor anthropogenic influence. For irrigation purposes, the USSL diagram suggests low to medium alkali hazards, Wilcox ratings range from permissible to excellent, and Doneen’s classification places the samples in Class I, indicating high permeability. Conclusion: Groundwater is generally unsuitable for drinking but remains acceptable for irrigation. Regular monitoring and effective management are essential to prevent further degradation and ensure long-term water sustainability.