Anthropogenic and agricultural activities are deteriorating drinking water quality of the Siling reservoir. Spatio-temporal variations and risk assessment of select heavy metals (Zn, Cu, Mn, Fe, Cr, Cd, and Pb) were investigated in water samples. During summer Mn (37.32 μg/L), Fe (41.0 μg/L), and Cd (1.18 μg/L) concentrations were higher in the water samples, while the concentrations of Zn (86.12 μg/L), Fe (42.0 μg/L), and Pb (30.82 μg/L) were dominant in winter. However, Cr exhibited elevated concentrations in both seasons. The health-risk assessment revealed that hazard quotient (HQ_ing) and hazard index (HI_ing) values were near to the acceptable limit, indicating non-carcinogenic risk to the recipient via oral intake of water. The calculated values for chronical daily intake (CDI) were found in the order of Cr > Fe > Mn > Zn > Cd in summer and Zn > Fe > Cr > Pb > Mn > Cu during winter. The carcinogenic risk (CR_ing) via ingestion route for Cr, Cd, and Pb were noted higher than the acceptable limit (10^-6). Multivariate statistical analysis such as cluster analysis (CA) and principal component analysis (PCA) results revealed that natural processes and anthropogenic activities were the main sources of water contamination. The data provided in this study are considered essential for reservoir remediation. The results suggested that quick action should be taken to protect the drinking water integrity of the Siling reservoir watershed from the different nonpoint pollution sources, especially the application of agricultural fertilizers.