---
title: "Major sources and selection factors"
subject: "Water Supply Engineering"
chapter: 2
key: "semester_5/water_supply_engineering:sources-and-selection-factors"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/sources-and-selection-factors
site: BCT Engineering
---

# Major sources and selection factors

Water Supply Engineering · Chapter 2: Sources of Water

- Asked in: 2078 Kartik, 3+3 marks; 2080 Baisakh, 2+2 marks (asked 2 times)
- Video: [Unit:2 | Criteria for the Selection of Source of Water | Diffe betn Ground Source & Surface Source |](https://www.youtube.com/watch?v=W-9Mrb5yeRw) — Prashant YT
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/sources-and-selection-factors
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-2

## Question

Discuss/list the major sources of water with respect to quantity and quality, briefly describing them with examples. What are the key factors to be considered while selecting a water source?

## Short answer

Major sources are rain, rivers, lakes, reservoirs, springs, wells, and infiltration galleries; surface sources are plentiful but need treatment, ground sources have limited yield but better quality. Selection depends on dry-season quantity, quality, distance and elevation for gravity flow, cost, reliability, protection, water rights, social acceptance, and environmental effects.

## Answer

#### Major sources of water
| Source | Quantity | Quality | Example |
|---|---|---|---|
| Rain water | Limited; seasonal | Fairly pure and soft but slightly acidic; picks up dust from roofs | Roof catchment tanks |
| Rivers and streams | Large, fluctuating | Turbid, soft, polluted downstream | Bagmati, Trishuli, Seti |
| Lakes and ponds | Moderate to large | Clear but may have algae | Phewa Lake (Pokhara) |
| Impounded reservoirs | Large and controlled | Good after settling | Kulekhani reservoir (Indra Sarovar) |
| Springs | Small to moderate | Clear, bacteriologically safe | Hill springs, dhunge dhara |
| Wells (shallow/deep) | Small to large | Hard, clear; shallow wells may be polluted | Tube wells in the Terai |
| Infiltration gallery | Small to moderate | Naturally filtered | River banks in the Kathmandu valley |

Surface sources are plentiful but need treatment; ground sources give better quality but their yield is limited.

#### Factors for selection of a source
1. **Quantity:** the yield in the dry season must satisfy the demand at the end of the design period.
2. **Quality:** wholesome, or easily treatable at low cost.
3. **Distance and elevation:** a short pipeline and a higher level for gravity flow, avoiding pumping.
4. **Cost:** construction, operation and maintenance.
5. **Reliability and protection:** perennial, and safe from pollution, floods and landslides.
6. **Water rights and social acceptance:** no conflict with existing users.
7. **Environmental effect:** minimum effect on downstream flow and ecology.

## Check yourself

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

1. Rain water as a source is:
   A. Large and constant
   B. Limited and seasonal; pure but soft and may pick up dust
   C. Hard and turbid
   D. Always polluted
   Answer: B. Rain water is limited, seasonal and soft. (Key point: Rain water)

2. Which generalisation is correct?
   A. Ground sources are plentiful but need treatment
   B. Surface sources are plentiful but need treatment; ground sources are better quality but limited
   C. Both have same quality
   D. Surface sources are always clean
   Answer: B. Surface water is plentiful but needs treatment while ground water has better quality but limited yield. (Key point: Surface vs ground)

3. Which is a key selection factor?
   A. Colour of the source
   B. Name of the river
   C. Dry-season yield meeting demand at end of design period
   D. Number of visitors
   Answer: C. Dry-season quantity is the first factor. (Key point: Selection factor)

## 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×
- [Criteria for selecting a water source](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aselection-criteria-water-source) — Water Supply Engineering, chapter 2, asked 5×
- [Pipe material selection factors; PPR pipes](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-material-factors-ppr) — Water Supply Engineering, chapter 8
- [Reservoir intake and site selection factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-intake-site-factors) — Water Supply Engineering, chapter 5, asked 2×
- [Convincing community on water source disputes](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apre-feasibility-water-disputes) — Water Supply Engineering, chapter 2

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