Source to Tap Assessment of Physicochemical and Microbiological Drinking Water Quality in Pokhara Metropolitan City, Nepal

Abstract

Ensuring the safety of drinking water requires not only expanded access but also sustained compliance with physicochemical and microbiological quality standards throughout the supply chain. This study presents a source-to-tap assessment of drinking water quality across major supply schemes serving wards 26–32 of Pokhara Metropolitan City, Nepal. A cross-sectional sampling design was adopted, covering surface and groundwater sources, reservoirs, and household taps operated under both centralized and community-managed systems. In total, 31 water samples (11 source, 5 reservoir, 15 household tap) were analysed for physical (pH, electrical conductivity, turbidity, total dissolved solids), chemical (total hardness, calcium, chloride, ammonia, iron, nitrate, arsenic, free residual chlorine), and microbiological (Escherichia coli, total coliform) parameters following Standard Methods for the Examination of Water and Wastewater (APHA, 24th ed.). Observed values were evaluated against the National Drinking Water Quality Standards (NDWQS, 2079) and WHO guidelines. Results indicate that most physicochemical parameters across schemes complied with national guideline values, reflecting generally acceptable chemical quality. Microbiological contamination was widespread: E. coli reached 51 CFU/100 mL at the LWSO surface intake, 18–22 CFU/100 mL at LWSO household taps, and was too numerous to count (TMTC) in the Chainapur and Malmul community schemes, while deep-borehole groundwater sources showed no detectable E. coli.In contrast, microbiological contamination was detected in several surface-water-based and community-managed schemes, with E. coli and total coliform counts exceeding permissible limits at multiple intake points and household taps. Free residual chlorine was detected only in the LWSO system and declined from ~0.34 mg/L in early distribution to undetectable at terminal taps; this decline was concurrent with higher microbial counts at consumer endpoints. Treated and groundwater-based supplies showed comparatively lower microbiological risk, underscoring the influence of source type, treatment, and distribution integrity on water safety.The findings highlight that compliance with physicochemical standards alone is insufficient to ensure safe drinking water in multi-scheme urban settings. Strengthening residual disinfection, protecting source waters, and prioritizing distribution-level monitoring are critical for reducing public health risks. This study provides localized evidence to support operational improvements and reinforces the importance of routine source-to-tap surveillance in heterogeneous water supply systems. This study provides localized evidence to support operational improvements and reinforces the importance of routine source-to-tap surveillance in heterogeneous water supply systems.