---
title: "Shallow and deep wells"
subject: "Water Supply Engineering"
chapter: 2
key: "semester_5/water_supply_engineering:shallow-deep-wells"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/shallow-deep-wells
site: BCT Engineering
---

# Shallow and deep wells

Water Supply Engineering · Chapter 2: Sources of Water

- Asked in: 2080 Bhadra, 2+2 marks; 2076 Chaitra, 4 marks; 2073 Shrawan, 4 marks; 2071 Chaitra, 4 marks (asked 4 times)
- Video: [SOURCES OF WATER - "WELLS",PART 13, ENVIRONMENTAL ENGINEERING](https://www.youtube.com/watch?v=jJb7tfcDFJk) — Vidhya Focus-2020
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/shallow-deep-wells
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-2

## Question

Differentiate between shallow and deep wells (with neat sketches), and describe their characteristics/suitability with respect to water quality and quantity. (Which of them would you prefer for a public water supply scheme and why?)

## Short answer

Shallow wells tap the upper unconfined aquifer, are up to 15 m deep, have small variable yield and poor bacteriological quality; deep wells tap confined aquifers below impervious layers, are deeper, with large steady yield and good quality. For public supply, prefer a deep well because of its reliable yield and better water quality.

## Answer

A **well** is a hole or shaft sunk into the ground to reach water-bearing strata. Wells are classified as shallow or deep by the stratum they draw from.

#### Sketches
```text
  SHALLOW WELL            DEEP (TUBE) WELL
  |  |  ground level      |  | ground level
  |  |                    |  |
  |~~|~ water table       |  | unconfined layer
  |__|                    |==|== impervious layer
  /////  impervious       |  |
                          |__| confined aquifer
                          (strainer at bottom)
```

#### Differences
| Basis | Shallow well | Deep well |
|---|---|---|
| Depth | Up to about 10 to 15 m | 30 m to hundreds of metres |
| Tapped stratum | Top (unconfined) aquifer above the first impervious layer | Confined aquifer below an impervious layer |
| Construction | Dug, lined with masonry or concrete rings | Drilled/bored with casing and strainer |
| Yield | Small (about 1 to 5 lps), depends on rainfall | Large and steady |
| Quality | Poor; likely to be polluted by bacteria | Good, free from bacteria, constant; often harder and may contain iron |
| Variation | Dries in the dry season | Rarely fails |
| Cost | Low | High |
| Use | Household and small rural supply | Municipal and industrial supply |

#### Suitability
- Shallow well water is filtered only by a thin soil layer, so bacteriological pollution from latrines and surface drainage is likely. The quantity is limited and varies with the water table.
- Deep well water is naturally filtered through a long path in the soil and is protected by the impervious cover. The quantity is large and dependable, though the water can be hard or contain iron because it is in contact with minerals for a long time.

#### Preferred choice
For a public supply scheme a **deep well (tube well)** is preferred because of its larger and more reliable yield, better quality (less treatment) and long life. Shallow wells serve only individuals or very small groups.

## Check yourself

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

1. A deep well draws water from:
   A. The top unconfined aquifer
   B. A confined aquifer below an impervious layer
   C. Surface runoff
   D. Rainwater tanks
   Answer: B. Deep wells tap confined aquifers below an impervious layer. (Key point: Tapped stratum)

2. Why is shallow well water likely to be polluted?
   A. It is filtered only by a thin soil layer
   B. It is very deep
   C. It is under pressure
   D. It has no strata
   Answer: A. Thin filtration means bacteriological pollution from latrines and surface drainage is likely. (Key point: Shallow well quality)

3. For a public supply a deep well is preferred because:
   A. It is cheaper to build
   B. It dries in summer
   C. Of larger, reliable yield and better quality needing less treatment
   D. It is dug by hand
   Answer: C. Deep wells give large steady yield, good quality and long life. (Key point: Preferred choice)

## 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×
- [Necessity and impacts of water supply scheme](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Anecessity-impacts-ws) — Water Supply Engineering, chapter 1, asked 3×
- [Objectives of supply; wholesome water requirements](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aobjectives-requirements-wholesome) — Water Supply Engineering, chapter 1, asked 2×
- [Settling tank 20 m long, 3.5 m deep; 0.02 and 0.01 mm](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ased-b79) — Water Supply Engineering, chapter 6, asked 3×
- [Short note: Infiltration wells](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ainfiltration-wells-note) — Water Supply Engineering, chapter 2
- [Water supply system and historical development](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aws-historical-development) — Water Supply Engineering, chapter 1

## Related in other subjects

- [Classify shallow and deep foundations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aclassify-foundations-soil) — Foundation Engineering, chapter 1, asked 4×
- [Deep foundation types and use of shallow foundations](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adeep-shallow-types-079a) — Building Technology, chapter 2
- [Shallow versus deep foundation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Ashallow-vs-deep-foundation) — Foundation Engineering, chapter 1
- [Differentiate GVF, RVF and SVF with sketches](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Adifferentiate-gvf-rvf-svf-sketch) — Hydraulics, chapter 5, asked 5×