---
title: "Water quality parameters and Nepal drinking water standards"
subject: "Environment and Pollution Control"
chapter: 4
key: "semester_7/environment_and_pollution_control:nepal-drinking-water-quality-standards"
source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/nepal-drinking-water-quality-standards
site: BCT Engineering
---

# Water quality parameters and Nepal drinking water standards

Environment and Pollution Control · Chapter 4: Water pollution

- Asked in: year not given, 4 marks
- Video: [Nepal Drinking Water Quality Standard | Different Parameters ,units & Concentration Limits | Nepali](https://www.youtube.com/watch?v=auW970qTYgo) — Civil Engineering Power
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/nepal-drinking-water-quality-standards
- Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-4

## Question

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.

## 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.

## Answer

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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why is the bacteriological test considered the most important?
   A. Pathogens cause immediate disease
   B. It is cheap only
   C. It measures taste
   D. Bacteria change pH
   Answer: A. Pathogens cause immediate disease, so faecal contamination must be absent. (Key point: Importance of bacteriological test)

2. The NDWQS limit for E. coli in drinking water is:
   A. 10 per 100 mL
   B. 0 per 100 mL
   C. 100 per 100 mL
   D. 50 per 100 mL
   Answer: B. Drinking water must have no E. coli or total coliform per 100 mL. (Key point: Coliform limit)

3. The NDWQS limits for pH and nitrate are:
   A. 6.5-8.5 and 50 mg/L
   B. 5-9 and 10 mg/L
   C. 6.5-8.5 and 500 mg/L
   D. 7 and 0 mg/L
   Answer: A. pH 6.5-8.5 and nitrate 50 mg/L (nitrate linked to blue baby syndrome). (Key point: pH and nitrate)

4. Coliforms are used as indicator organisms because:
   A. They are the only pathogens
   B. They are easy to detect and live in the human gut
   C. They are chemical
   D. They cause turbidity
   Answer: B. They are easy to test for and indicate faecal contamination. (Key point: Why coliforms)

## Related in Environment and Pollution Control

- [Physical and chemical characteristics of solid waste](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Asolid-waste-characteristics) — Environment and Pollution Control, chapter 5
- [Montreal Protocol and control of ODS in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Amontreal-protocol-nepal-ods-control) — Environment and Pollution Control, chapter 7

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