---
title: "Schematic diagram of rural gravity scheme"
subject: "Water Supply Engineering"
chapter: 1
key: "semester_5/water_supply_engineering:rural-gravity-scheme-diagram"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/rural-gravity-scheme-diagram
site: BCT Engineering
---

# Schematic diagram of rural gravity scheme

Water Supply Engineering · Chapter 1: Introduction

- Asked in: 2078 Kartik, 4 marks; 2080 Bhadra, 4 marks; 2079 Baisakh, 4 marks; 2073 Chaitra, 4 marks; 2075 Chaitra, 4 marks (asked 5 times)
- Video: [Unit:1 | Systematic Flow diagram of Rural Water Supply Scheme | Water Supply Eng | BE Civil |](https://www.youtube.com/watch?v=ZkDPytgnYFE) — 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/rural-gravity-scheme-diagram
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-1

## Question

Draw a schematic diagram of a typical gravity water supply system for a rural (hilly) area of Nepal and briefly describe the function of each component.

## Short answer

Gravity scheme: higher spring → spring box → sedimentation tank → reservoir (stores 33-50% daily demand, chlorination) → break pressure tank (if head >60m) → distribution pipes with valves → public tap stands. Functions: intake protects source, sedimentation removes silt, reservoir balances demand, BPT reduces pressure, valves release air and drain sediment.

## Answer

A gravity water supply system uses the natural fall of the ground from a high-level source to carry water to the village without pumping. It is the most common, cheapest and most reliable scheme in the hills of Nepal.

#### Schematic diagram
```text
  Spring (high level)
       |
  [Spring box / Intake]
       |  pipe (GI/HDPE)
  [Sedimentation tank]
       |
  [Valve + Reservoir tank] <- chlorination
       |
  [Break pressure tank] (if head > 60 m)
       |
  Distribution pipes with air/wash valves
       |
  [Tap stands / Public standposts]
```

#### Function of components
1. **Source (spring/stream):** gives the required yield throughout the year and is usually at a higher level than the village.
2. **Intake / spring box:** collects the spring water, protects it from pollution, has an overflow and a washout, and controls the flow into the pipe.
3. **Transmission pipeline:** carries water by gravity to the tank. Pipes are laid below ground where possible.
4. **Sedimentation tank:** settles silt and sand, especially for stream sources, before the water enters the reservoir tank.
5. **Reservoir (storage) tank:** stores water to balance the continuous inflow against the variable demand, commonly 33 to 50 percent of the daily demand. Disinfection (chlorination) is usually done here.
6. **Break pressure tank (BPT):** reduces the static head to atmospheric pressure so that pipes and fittings are not overstressed.
7. **Valves (air, wash-out, sluice, reflux):** release trapped air at high points, drain sediment at low points, control the flow and prevent back flow.
8. **Distribution pipes:** carry water from the tank to the settlements.
9. **Tap stands / public standposts:** the points where users collect water, with a soak pit for waste water.

## Check yourself

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

1. What makes a gravity water supply system cheap and reliable in the hills?
   A. Electric pumps lift water uphill
   B. Natural fall from a high-level source carries water without pumping
   C. Water is treated by full coagulation and filtration
   D. Water is stored only in underground tanks
   Answer: B. The natural fall of ground from a high source carries water to the village without pumping. (Key point: Gravity system principle)

2. What is the role of air valves and wash-out valves in the pipeline?
   A. Air valves drain sediment; wash-out valves release air
   B. Both increase the flow rate
   C. Air valves release trapped air at high points; wash-outs drain sediment at low points
   D. Both prevent back flow
   Answer: C. Air valves release trapped air at high points and wash-outs drain sediments at low points; reflux valves prevent back flow. (Key point: Valves)

3. The reservoir tank in a rural scheme is provided mainly to:
   A. Meet the difference between continuous inflow and variable demand
   B. Reduce static head to atmospheric pressure
   C. Settle silt from stream water
   D. Collect water from the spring
   Answer: A. It stores water to balance continuous inflow against variable demand, commonly 33 to 50 percent of daily demand. (Key point: Reservoir tank capacity)

## Related in Water Supply Engineering

- [Rural and urban scheme layout diagram](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Arural-urban-scheme-diagram) — Water Supply Engineering, chapter 1, asked 6×
- [Typical water supply system and components](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Atypical-ws-system-components) — Water Supply Engineering, chapter 1, asked 4×
- [Intake type for hilly area of Nepal](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aintake-for-hilly-area) — Water Supply Engineering, chapter 5, asked 2×
- [Rural area 22000 L/day river supply (question text cut)](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ares-a76) — Water Supply Engineering, chapter 7
- [Sources for hilly rural areas; river vs spring](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahilly-rural-sources-river-spring) — Water Supply Engineering, chapter 2
- [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×

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