This study investigated the physico-chemical parameters of drinking water of Kathmandu Valley, Nepal, analyzing samples from tap water, tube-well water, and dug well water. A total of 720 samples were collected in 2021, comprising 240 samples each from tap water, tube well water, and dug wells water. The parameters tested included temperature, turbidity, color, pH, total alkalinity, total hardness, iron, ammonia, and chloride concentrations. The findings revealed variable water quality across different sources and seasons. Turbidity was highest in dug well water during summer (3.28±0.27 NTU) nephelometric turbidity unit and the lowest in tap water (2.07±0.32 NTU). Color intensity was greater in dug well water (2.65±0.22 TCU) true color units compared to tap water (1.3±0.25 TCU) during autumn. The pH values indicated that tube-well water was more alkaline in summer (8.2±0.28) and less in autumn (7.3±0.26). Alkalinity peaked in dug well water in summer (399.25±107.09 mg/L) and was lowest in tap water during winter (129±18.04 mg/L). Total hardness was significantly higher in dug well water during summer (294.75±169.65 mg/L) and lower in tap water in winter (135±36.72 mg/L). Iron content was substantially higher in dug well and tube well waters in summer (2.8±0.49 mg/L) compared to tap water (0.2±0.05 mg/L). Ammonia levels were alarmingly high in dug well water in winter (55.12±30.84 mg/L), but minimal in tap water during autumn and winter (0.85±0.32 mg/L). Chloride was found in high concentrations in dug well water in spring (75.86±9.45 mg/L) and lower in tap water during summer (25.16±10.98 mg/L). This study shows the variability and potential risks associated with drinking water quality in Kathmandu Valley, indicating the need for regular monitoring and water quality improvement measures