---
title: "Drinking water standards and WHO guidelines"
subject: "Water Supply Engineering"
chapter: 4
key: "semester_5/water_supply_engineering:who-guidelines-standards"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/who-guidelines-standards
site: BCT Engineering
---

# Drinking water standards and WHO guidelines

Water Supply Engineering · Chapter 4: Quality of Water

- Asked in: 2079 Bhadra, 4 marks; 2075 Asoj, 4 marks (asked 2 times)
- Video: [Drinking Water Standards: IS 10500 | Water Quality Parameters | Environmental Engg | Deependra Sir](https://www.youtube.com/watch?v=gk8Xd6Jc-v8) — Civil Yodha by Unacademy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/who-guidelines-standards
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-4

## Question

Define water quality standards for drinking purposes. Discuss the significance of WHO guidelines for drinking water quality.

## Short answer

Water quality standards are legally set maximum permissible levels of physical, chemical, and biological parameters to ensure safe drinking water. WHO guidelines provide health-based values, serve as a scientific basis for national standards, promote Water Safety Plans, and guide monitoring and treatment to protect public health.

## Answer

#### Water quality standards for drinking water
Water quality standards are the maximum (or minimum) permissible values of the physical, chemical and biological characteristics of drinking water that make it safe for human consumption. They are set by law so that water supplied to the public does not harm health and is acceptable to the user. In Nepal, the **National Drinking Water Quality Standards (NDWQS) 2062 BS** apply; many countries follow the WHO guidelines.

Examples (Nepal standard): turbidity 5 NTU (maximum 10), pH 6.5 to 8.5, TDS 1000 mg/l, hardness 500 mg/l, chloride 250 mg/l, iron 0.3 mg/l, arsenic 0.05 mg/l, nitrate 50 mg/l, residual chlorine 0.1 to 0.2 mg/l, and E. coli 0 per 100 ml.

#### Significance of WHO guidelines
1. **Scientific basis:** The WHO "Guidelines for Drinking-water Quality" give health-based guideline values drawn from toxicology and epidemiology reviews and are updated periodically.
2. **Basis for national standards:** Countries, including Nepal, adapt them to local conditions, cost and risks.
3. **Public health protection:** Guideline values for E. coli (zero per 100 ml), arsenic (0.01 mg/l), fluoride (1.5 mg/l), nitrate (50 mg/l), lead (0.01 mg/l) and other substances help prevent acute and chronic disease.
4. **Risk-based approach:** They promote Water Safety Plans, covering catchment to tap, instead of only end-product testing.
5. **Guides for monitoring and treatment:** They help in selecting treatment, monitoring frequency and emergency response.
6. **Basis for comparison and planning:** They permit comparison of supplies and set targets for developing countries.

## Check yourself

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

1. Drinking water quality standards are:
   A. permissible limits of physical, chemical and biological characteristics for safe consumption
   B. only taste preferences
   C. treatment plant designs
   D. rules for pipe diameters
   Answer: A. They are set by law to protect health. (Key point: Standards definition)

2. WHO guideline values are based on:
   A. local pipe costs only
   B. toxicology and epidemiology reviews, updated periodically
   C. taste surveys only
   D. nothing scientific
   Answer: B. They are health-based values. (Key point: WHO guideline basis)

3. Countries like Nepal use WHO guidelines to:
   A. copy without change
   B. ignore for monitoring
   C. adapt them into national standards for local conditions
   D. replace sanitation
   Answer: C. Local risks and costs shape national standards. (Key point: National use)

4. The risk-based approach promoted by WHO is:
   A. testing only the end product
   B. treating all water the same
   C. removing all minerals
   D. Water Safety Plans from catchment to tap
   Answer: D. This avoids relying only on final testing. (Key point: Risk approach)

## Related in Water Supply Engineering

- [Water sources: quality and quantity](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Asources-quality-quantity) — Water Supply Engineering, chapter 2, asked 3×
- [Aeration purposes; Fe/Mn removal; residual chlorine](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aaeration-iron-residual-chlorine) — Water Supply Engineering, chapter 6
- [Why groundwater; quality parameters](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Agroundwater-source-quality-parameters) — Water Supply Engineering, chapter 2
- [E-coli: harmful? why and how tested](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aecoli-harmful-tested) — Water Supply Engineering, chapter 4, asked 3×

## Related in other subjects

- [Water quality parameters and Nepal drinking water standards](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Anepal-drinking-water-quality-standards) — Environment and Pollution Control, chapter 4
- [Water fit for drinking; test on water](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awater-fit-for-drinking) — Concrete Technology and Masonry Structure, chapter 1
- [SQA plan and quality standards](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Asqa-plan-standards) — Software Engineering, chapter 9
- [Why quality standards are needed](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Aquality-standards-need) — Software Engineering, chapter 9