Assessment of groundwater quality using water quality index (WQI): A case study of a hard rock terrain in Sri Lanka

Chronic Kidney Disease of uncertain etiology (CKDu) is a widespread health issue in rural dry zone regions in Sri Lanka. Monaragala region, located in eastern Sri Lanka is one of the hardest hit areas with CKDu. In order to investigate the possible relationship between the incidence of CKDu and drinking water quality, 99 groundwater samples from deep boreholes and shallow wells in hard rock aquifers in the Monaragala region, were collected and analysed for major cations and anions, and some selected trace element contents. The results revealed that over 65% of the groundwater samples from Monaragala area were alkaline. The anions in groundwater varied as HCO3- > Cl- > SO42- > F- while cations varied in the order of Na > Ca > Mg > K. The Majority of the samples (75%) belong to the Ca2+-Mg2+ - HCO3 type. Among the studied parameters, electrical conductivity, chloride, sulphate, hardness, fluoride exceeded the WHO recommended values for drinking water in most cases. For instance, 76% of wells in the study area showed fluoride levels higher than the recommended levels (0.5 mg/L) for Sri Lanka. The higher ion contents in groundwater were mainly due to dissolution of aquifer minerals and a higher rate of evaporation. The calculation of Water Quality Index (WQI) indicated that over 50% of groundwater samples of the study area are poor in quality. The higher values of WQI also overlap with high prevalence areas of CKDu. This work revealed that groundwater quality has a direct effect on the etiology of CKDu in the region.