---
title: "Planning of distribution; intermittent supply"
subject: "Water Supply Engineering"
chapter: 7
key: "semester_5/water_supply_engineering:distribution-planning-intermittent"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/distribution-planning-intermittent
site: BCT Engineering
---

# Planning of distribution; intermittent supply

Water Supply Engineering · Chapter 7: Reservoirs and Distribution System

- Asked in: 2075 Chaitra, 8 marks
- Video: [24×7 Water Supply Projects in India | How Cities Get Continuous Water Supply? | Explained](https://www.youtube.com/watch?v=XRoj-vwf3jA) — The Civil Mentor 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/distribution-planning-intermittent
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-7

## Question

What are the general considerations to be observed in the planning of distribution system? Under what condition would you recommend the use of intermittent system of water supply? What are its drawbacks?

## Short answer

General considerations include demand, source, layout, pressure, velocity, reservoir, appurtenances, quality. Intermittent system is used when source yield is limited or pumping is costly; drawbacks include water quality issues, larger pipes, and supply interruptions.

## Answer

#### General considerations in planning a distribution system
1. **Demand:** population and demand for the design period, with peak factors and fire demand.
2. **Source and topography:** position of the source and reservoir, and ground levels, to decide between gravity, pumping or a combination.
3. **Layout:** choose dead end, grid iron, ring or radial layout to suit the roads and the town plan.
4. **Pressure:** keep the residual head at least 10–15 m at the tap (7–10 m for rural stand posts) and the maximum pressure about 60–70 m, using zoning or BPT if more.
5. **Velocity:** 0.6–3 m/s in the pipes.
6. **Reservoir:** provide balancing, emergency and fire storage at a suitable high point close to the demand.
7. **Appurtenances:** sectional valves, air valves, scour valves at low points and dead ends, and hydrants.
8. **Quality protection:** avoid dead ends, cross connections and low spots where water stagnates.
9. **Materials and cost:** pipe material, class and cost; ease of operation and maintenance; future expansion.

#### When intermittent supply is recommended
1. When the source yield is limited and cannot provide for the continuous 24 h supply (for example in dry-season springs).
2. When the pumping is costly or the power supply is available only for a few hours.
3. When the head available in the system is small and only part of the area can be given water at a time (zone-by-zone rotation).
4. When the treatment capacity is small, or in the early years when the network is incomplete.
5. In small or rural towns where consumers can store water without difficulty.

#### Drawbacks of the intermittent system
1. Pipes are empty during the off period, so polluted water can be sucked in through leaks, and quality is poor.
2. Larger pipes, valves and meters are required, because the whole day's demand is delivered in a few hours.
3. Consumers must store water, which wastes space and can become contaminated.
4. No water for fire fighting during the off period.
5. Frequent pressure change and wet–dry cycles cause corrosion and pipe damage; air in the pipes distorts meter readings.
6. Supply is unfair to people at the far ends or on high ground.

## Check yourself

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

1. Which is a general planning consideration for a distribution system?
   A. Colour of pipes
   B. Demand with peak factors, source and topography, layout, pressure and velocity limits, reservoir and appurtenances
   C. Number of consumers who own tanks only
   D. Colour of water
   Answer: B. These technical factors decide the layout and design. (Key point: Planning factors)

2. When is an intermittent supply recommended?
   A. When the source yield is large and power is unlimited
   B. When source yield is limited or power is available only for a few hours
   C. When fire demand is high
   D. When the town is fully planned with continuous pumping
   Answer: B. Limited yield, costly or short power supply, or small available head favour intermittent supply. (Key point: When intermittent)

3. Why is water quality poor in an intermittent system?
   A. Chlorine is overdosed
   B. Empty pipes can suck in polluted water through leaks during the off period
   C. Pipes are too large
   D. The water is too cold
   Answer: B. Pressure is lost in the off period, so contaminants enter through leaks. (Key point: Contamination)

4. Why does an intermittent system need larger pipes, valves and meters?
   A. Because pressure is lower
   B. Because the whole day's demand is delivered in a few hours
   C. Because velocity must be below 0.6 m/s
   D. Because of fire demand only
   Answer: B. Delivering 24 h demand in a few hours needs higher flow rates. (Key point: Pipe size)

## Related in Water Supply Engineering

- [Balancing reservoir, intermittent supply 7-10 and 17-20](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ares-c74) — Water Supply Engineering, chapter 7
- [Continuous vs intermittent supply](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Acontinuous-vs-intermittent) — Water Supply Engineering, chapter 7, asked 5×
- [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
- [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×
- [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×
- [Protection and maintenance of water supply](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aws-maintenance-types) — Water Supply Engineering, chapter 7, asked 4×

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