Multivariate Assessment of Groundwater Hydrochemistry for Drinking and Irrigation in the Flood-Prone District Dadu, Sindh, Pakistan

Groundwater quality in the flood-prone District Dadu, Sindh, was evaluated through an integrated physicochemical, microbiological, irrigation, and multivariate assessment. A total of 159 groundwater samples from subdistrict Khairpur Nathan Shah were analyzed against the WHO, NDWQS, and international irrigation guidelines. Results showed that although pH remained within acceptable limits, severe salinity, hardness, and ion-exchange processes dominated the hydrochemistry, with TDS reaching 22,900 mg/L and chloride up to 6357 mg/L. Microbial contamination was widespread, with total coliforms detected in 87.4% of samples and <i>Escherichia coli</i> in 59.7%, including TNTC counts in 17% of sources. Irrigation indices (SAR, RSC, PI, MAR) were largely suitable, yet Na%, KI, SSP, and Cl^-/SO₄ ^2- ratios revealed elevated sodicity hazards, particularly in UC Parya. PCA identified five major hydrochemical processes, salinity-major ion mineralization, physicochemical interactions, microbial contamination, Fe-related redox processes, and As geochemical mobilization, explaining 76.7% of the variance. HCA grouped samples into four distinct water quality clusters consistent with these processes. QMRA indicated high infection probabilities for all population groups, while hazard quotient analyses highlighted elevated fluoride and arsenic risks, especially for infants and children. Overall, the study reveals that groundwater in Khairpur Nathan Shah is significantly impaired for drinking and variably suitable for irrigation, underscoring the urgent need for improved water supply, treatment interventions, and sustainable aquifer management in rural Sindh.