Evaluation of surface water and groundwater quality for drinking purposes using the water quality index: a case study of Kathmandu Valley, Nepal

ABSTRACT Surface water and groundwater are the two primary water supply sources for household purposes in Kathmandu Valley. This study is based on the assessment of physiochemical parameters and the determination of the water quality index (WQI) of 76 water sources (22 surface water and 54 groundwater) used for public water supply in Kathmandu Valley. Samples were collected during May–July 2024. Five physical properties (turbidity, pH, color, taste and odor, and electrical conductivity) and 12 chemical parameters (iron, manganese, arsenic, fluoride, ammonia, chloride, sulphate, nitrate, copper, zinc, aluminum, and total hardness) were analyzed. It was observed that 68.2% of surface water samples and 11.1% of groundwater samples were as per the standards. The WQI values ranged from 0.05 to 73.19 (surface water samples) and 0.58 to 872.08 (groundwater samples). Correlation analysis revealed strong correlation of WQI with iron (r = 0.94), turbidity (r = 0.81) and manganese (r = 0.8). The findings of this study suggest that water from these sources requires treatment, along with measures to protect sources from additional contamination risks.