---
title: "Short note: Water supply and distribution system"
subject: "Building Technology"
chapter: 12
key: "semester_6/building_technology:water-distribution-short"
source: https://www.bctengineer.com/q/semester_6/building_technology/water-distribution-short
site: BCT Engineering
---

# Short note: Water supply and distribution system

Building Technology · Chapter 12: Other services in building

- Asked in: 2065 Shrawan (old course), 4 marks; 2062 Baisakh (old course), 4 marks (asked 2 times)
- Video: [Water Distribution | System Design and Layout](https://www.youtube.com/watch?v=f2faanH0_Ww) — American Water College
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/water-distribution-short
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-12

## Question

Write a short note on water supply (distribution) system and its design.

## Short answer

Water distribution systems include direct up-feed from mains, indirect down-feed with sump, pump and overhead tank (common in Nepal), combined, and hydropneumatic. Design considers daily demand (e.g., 135 L/person), storage sizing, pipe sizing using Hazen-Williams for velocity 0.9-2.4 m/s, and minimum residual head 3-5 m.

## Answer

**Water supply in buildings** brings treated water from the public main (or a well/tank) to taps and fixtures in adequate quantity and at adequate pressure.

#### Systems of distribution
1. **Direct (up-feed) system:** water comes straight from the main to the fixtures; used where mains pressure is sufficient and supply is continuous. Cheap, but there is no storage and the pressure varies.
2. **Indirect (down-feed) system:** water is first stored in an underground sump, pumped to an overhead tank on the roof, and distributed by gravity. Used in multistorey buildings and where supply is intermittent (usual in Nepal).
3. **Combined system:** a mix of both; ground-floor taps are fed directly, upper floors via the tank.
4. **Hydropneumatic system:** a pressure vessel and pump, with no overhead tank.

```text
 Main -> [sump] -> pump -> [overhead tank] -> down pipes
                                   |-> floors / fixtures
```

#### Design
1. **Demand:** 135 L/person/day for residences (NBC/IS 1172); offices 45 L; schools 45 L; hospitals about 340 L per bed.
2. **Storage:** overhead tank about 1/3 of the daily demand; underground sump 1/2 to 1 day's demand.
3. **Pipes:** sizes chosen from demand and velocity (0.9-2.4 m/s); pressure loss computed by the Hazen-Williams equation; minimum residual head at the highest tap about 3-5 m.
4. **Layout:** short, straight runs; valves on branches; pipes (GI/HDPE/PVC/CPVC) in ducts, not under foundations; provision of air release and drain valves.

## Check yourself

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

1. Why is the indirect (down-feed) system usual in Nepal?
   A. Supply is intermittent, so water is stored in a sump and overhead tank
   B. Mains pressure is always high
   C. Storage is not allowed
   D. Pumps are unnecessary
   Answer: A. Water is pumped to an overhead tank and distributed by gravity. (Key point: Indirect system)

2. Direct system suits:
   A. Continuous supply with sufficient mains pressure
   B. Intermittent supply
   C. Very tall buildings
   D. Low pressure
   Answer: A. It has no storage. (Key point: Direct system)

3. Residential demand is about:
   A. 45 L
   B. 135 L/person/day
   C. 340 L
   D. 10 L
   Answer: B. Offices and schools 45 L. (Key point: Demand)

4. Typical storage sizing:
   A. Overhead 3 days
   B. No sump
   C. Overhead tank about 1/3 daily demand; sump 1/2 to 1 day
   D. Sump 1 hour
   Answer: C. As per design guidelines. (Key point: Storage)

## Related in Building Technology

- [Principles of laying out water supply system](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awater-supply-principles) — Building Technology, chapter 12
- [Water supply and sanitation management](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awater-supply-sanitation) — Building Technology, chapter 12
- [Domestic water supply and drainage systems](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awater-supply-drainage) — Building Technology, chapter 12
- [Domestic water supply; septic tank and soak pit](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awater-supply-septic-067as) — Building Technology, chapter 12

## Related in other subjects

- [Design steps and criteria of distribution system](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adistribution-design-steps) — Water Supply Engineering, chapter 7, asked 3×
- [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×
- [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
- [Planning of distribution; intermittent supply](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adistribution-planning-intermittent) — Water Supply Engineering, chapter 7