---
title: "Short note: Infiltration wells"
subject: "Water Supply Engineering"
chapter: 2
key: "semester_5/water_supply_engineering:infiltration-wells-note"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/infiltration-wells-note
site: BCT Engineering
---

# Short note: Infiltration wells

Water Supply Engineering · Chapter 2: Sources of Water

- Asked in: 2067 Asar (old course)
- Video: [Infiltration Wells | Water Supply Engineering | Civil Polytechnic / Diploma](https://www.youtube.com/watch?v=lcfDJvKOLfA) — Polytechnic Class (READBY) 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/infiltration-wells-note
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-2

## Question

Write a short note on infiltration wells.

## Short answer

Infiltration wells are shallow open wells dug in a river bed or bank to collect water filtered through sand and gravel, connected to a common sump well by pipes. They are cheap, yield moderate water, but clogging reduces yield over time, so periodic cleaning is needed; used for small town and rural supplies.

## Answer

**Infiltration wells** are shallow, open, circular wells dug in the bed or bank of a river (or near a lake) in permeable sand and gravel, to collect water that has been filtered through the bed or bank material. They are sunk in a group and joined to a common sump (jack) well by horizontal pipes or by a gallery, and the water is pumped from the sump.

#### Construction
- Wells of 3 to 4.5 m diameter are lined with brick masonry with open joints or with concrete rings having perforations (weep holes) in the lower part.
- The bottom is usually left open (not sealed) and covered with a graded gravel layer, so that water enters through the bottom as well as the sides. The wells are sunk a few metres below the water level.
- The top is covered above the highest flood level, with a manhole for access.
- Several wells are located in a line, 20 to 30 m apart, and connected to the collecting well by porous or siphon pipes.

```text
 river ~~~~~~~~~~~~~
 =========================  bank
  [W1]   [W2]   [W3]
    \     |     /   siphon/pipe
     \    |    /
       [Sump well] ---> pump
```

#### Features
- The water is cleaner and clearer than the river water because it is filtered by the bed and bank sand.
- The yield is moderate and depends on the permeability of the soil and on the river level.
- The wells are cheap to build, but clogging reduces the yield with time, so periodic cleaning or development is needed.
- Used for small town and rural supplies, mostly in the Terai and along rivers.

## Check yourself

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

1. What kind of water do infiltration wells collect?
   A. Water filtered through permeable sand and gravel of the river bank or bed
   B. Raw river water drawn directly from the surface
   C. Deep confined aquifer water under artesian pressure
   D. Rain water collected from the roof of the well
   Answer: A. They are sunk in permeable bank or bed material, so the water has been filtered through the sand and gravel before entering. (Key point: What infiltration wells collect)

2. How is water from a group of infiltration wells brought to the pump?
   A. Each well has its own pump
   B. The wells are joined to a common sump well by horizontal or siphon pipes or a gallery, and pumped from the sump
   C. The wells discharge directly into the river
   D. Water flows by gravity straight to the consumers
   Answer: B. Several wells are connected to one collecting sump well and the pump works from the sump. (Key point: Layout and collection)

3. Which statement about the construction of an infiltration well is correct?
   A. Lined with perforated rings in the upper part only and left open at the bottom
   B. Located 2 to 3 m apart in a single well
   C. Lined with perforated (weep hole) rings in the lower part, bottom plugged with concrete, top covered above highest flood level
   D. Built with a solid lining and no openings so water enters from the top
   Answer: C. Weep holes are in the lower part, the bottom is plugged with concrete, and the top is raised above flood level. (Key point: Construction details)

4. Why do infiltration wells need periodic cleaning or development?
   A. Clogging of the bank material reduces the yield with time
   B. The pumps wear out quickly
   C. The water becomes too clear
   D. The wells float up during floods
   Answer: A. Clogging reduces yield with time, so cleaning or development restores it. (Key point: Limitations)