- Practice · 4 marks
Water quality parameters and Nepal drinking water standards
Short answer
Drinking water quality is assessed by physical (turbidity ≤5 NTU), chemical (pH 6.5–8.5, TDS ≤1000 mg/L, nitrate ≤50 mg/L, arsenic ≤0.05 mg/L) and biological parameters (E. coli 0/100 mL). These Nepal standards ensure safety, with coliform absence being the most critical indicator of faecal contamination.
Describe the important physical, chemical and biological parameters used to assess water quality. Mention the typical limits of the National Drinking Water Quality Standards of Nepal.
Water quality is judged by comparing measured parameters with the standards for the intended use. Nepal's National Drinking Water Quality Standards (NDWQS, 2062 BS / 2005) give the maximum concentrations allowed in drinking water; the values below are the typical NDWQS limits. A value in brackets is acceptable only when no better alternative source is available.
| Group | Parameter | Significance | Nepal NDWQS limit |
|---|---|---|---|
| Physical | Turbidity | Cloudiness from suspended matter; shields microbes | 5 NTU (10) |
| Physical | Colour, taste, odour | Acceptability | 5 TCU (15) colour; no objectionable taste/odour |
| Physical | Temperature | Affects reaction rates, oxygen | - |
| Chemical | pH | Acidity/alkalinity, corrosion | 6.5-8.5 |
| Chemical | Total dissolved solids | Mineral content, taste | 1000 mg/L |
| Chemical | Chloride | Salinity, taste | 250 mg/L |
| Chemical | Nitrate | Blue baby syndrome | 50 mg/L |
| Chemical | Iron | Taste, staining | 0.3 mg/L (3) |
| Chemical | Arsenic | Toxic, carcinogenic | 0.05 mg/L |
| Chemical | Ammonia | Pollution indicator | 1.5 mg/L |
| Chemical | DO, BOD, COD | Organic pollution | - (stream standards) |
| Biological | E. coli / thermotolerant coliform | Faecal contamination indicator | 0 per 100 mL |
| Biological | Total coliform | General bacterial quality | 0 per 100 mL (in 95% of samples) |
The bacteriological test is the most important because pathogens cause immediate disease. Coliforms are used as indicator organisms because they are easy to detect and are present in large numbers in the human gut.
✓ Answer checked by Claude Opus 5.5 (high effort)
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