Sarkar et al. 2022 — Drinking water quality in Kathmandu Valley, Nepal
This observational study measures bacterial and multi-metal chemical contamination across 35 drinking water sources in Nepal’s Kathmandu Valley, combined with a health and taste-preference survey of 146 households (603 individuals) using those sources. The study reports widespread bacterial contamination (94% of sources positive for total or fecal coliform) and exceedances of Nepal Drinking Water Quality Standards and WHO Drinking-Water Guidelines for aluminum, arsenic, iron, and manganese. Uranium is measured and reported but does not exceed WHO guideline values at these sites. The authors find that taste ratings by consumers are not correlated with iron or manganese concentrations, raising public-health concerns about WHO’s reliance on aesthetic criteria rather than formal health-based limits for these metals.
Key numbers
Sources sampled: n=35 (7 dug wells, 18 tube wells, 9 stone spouts, 1 municipal tap); all unfiltered to represent ingestion exposure including distribution-system contributions.
Metals analyzed by ICP/MS (EPA Method 200.8): Al, As (total), Ba, Be, B, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Tl, U, V, Zn. Iron by flame AAS. Note: arsenic reported as total As; speciation to iAs not performed.
Exceedances of Nepal or WHO guideline values:
- Aluminum: max 0.53 mg/L (WHO aesthetic guideline 0.2 mg/L)
- Arsenic: max 0.071 mg/L (WHO guideline 0.01 mg/L; Nepal standard 0.05 mg/L)
- Iron: max 7.22 mg/L (WHO aesthetic guideline 0.3 mg/L)
- Manganese: max 3.229 mg/L (WHO health-based guideline 0.08 mg/L; Nepal standard 0.2 mg/L)
No exceedances reported for Cd, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se, Tl, U, V, or Zn at these 35 sources.
Geographic pattern: high As, Fe, and Mn sources are associated with floodplain deposits (Gokarna Formation and recent alluvial sediments along the Bagmati and Manohara rivers), consistent with reductive dissolution of iron oxyhydroxides releasing adsorbed As and Mn in reducing aquifer conditions.
Consumer taste preference: no statistically significant correlation between household taste ratings and iron or manganese concentrations. Mixed-effects logistic regression: consumers of sources with both high and low Mn concentrations were less likely to have positive attitudes toward school than those with moderate Mn concentrations; education (years of schooling) was the strongest social predictor of individual health outcomes. Arsenic exposure at these levels was not yet associated with reported arsenicosis cases in the valley.
Methods (brief)
Analytical method: ICP/MS (PerkinElmer ELAN DRC II with ESI SC-4DX FAST injection) for metals per EPA Method 200.8; flame AAS for iron; ion-selective electrode for fluoride. Laboratory: Vermont Department of Health Laboratory (NELAP-accredited, SDWA-certified). Samples collected unfiltered in 250 mL glass bottles; preserved with concentrated HNO3 (pH <2) for chemical analyses; stored on ice during transport from Kathmandu to Vermont. QA/QC: known-addition standards, reagent blanks, duplicate samples. Bacterial analysis by membrane filtration at Tribhuvan University in Kathmandu (same-day analysis). Statistical analyses in R 4.0.4; mixed-effects logistic regression for health outcomes; Kruskal-Wallis tests for non-normal distributions. Sample size limited by post-earthquake road access constraints; partly based on a stratified random design overlapping with a 2012–2013 field study.
Implications
Certification: Drinking water is a direct exposure route for heavy metals in communities relying on groundwater. The As exceedances documented here (max 0.071 mg/L, more than 7× the WHO guideline) in a post-earthquake setting illustrate the vulnerability of groundwater-dependent populations. For HMT&C, this paper is more relevant as regulatory context and exposure background than as a direct product concentration source.
Courses: Strong case study for a drinking-water heavy metals module: the disconnect between taste perception and Mn/Fe concentration illustrates why aesthetic-based regulatory thresholds are insufficient protection; the floodplain geology–As/Mn association illustrates natural geogenic contamination pathways distinct from agricultural or industrial sources.
App: Not directly applicable to food ingredient contamination profiles. Relevant as background for an exposure-route section on drinking water contributions to total dietary metal intake, particularly for As, Mn, and Al.