---
title: "Balancing tank: village 80000 L/day, spring 0.8 lps"
subject: "Water Supply Engineering"
chapter: 7
key: "semester_5/water_supply_engineering:res-b79"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/res-b79
site: BCT Engineering
---

# Balancing tank: village 80000 L/day, spring 0.8 lps

Water Supply Engineering · Chapter 7: Reservoirs and Distribution System

- Asked in: 2079 Bhadra, 8 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/res-b79
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-7

## Question

A village has a design year demand of 80000 liter per day. This demand is to meet by continuous system of supply from a spring source with safe yield 0.8 lps. The consumption pattern is as follows:

| Time: hour | Consumption % |
|---|---|
| 5.00 - 7.00 | 20 |
| 7.00 - 12.00 | 30 |
| 12.00 - 17.00 | 20 |
| 17.00 - 19.00 | 25 |
| 19.00 - 5.00 | 5 |

Is a balancing storage tank necessary? Calculate its capacity if necessary.

## Short answer

Daily demand 80 m3, spring yield 69.12 m3/day (deficit). Assuming inflow = demand/24 = 3.33 m3/h, peak rates exceed inflow. Balancing capacity by mass curve = 29.33 m3 (adopt 30 m3).

## Answer

#### Given data
- Daily demand = 80,000 L = 80 m³/day
- Spring safe yield = 0.8 lps = 0.8 × 86,400 = 69,120 L/day = 69.12 m³/day (2.88 m³/h)
- Demand: 5–7 h 20%, 7–12 h 30%, 12–17 h 20%, 17–19 h 25%, 19–5 h 5%

#### Check of source and need of storage
The yield (69.12 m³/day) is **less** than the demand (80 m³/day), a shortage of 10.88 m³/day (13.6%). A storage tank cannot remove this shortage; another source or a reduced demand is needed. To balance the hourly variation, the inflow is taken equal to the demand (80/24 = 3.33 m³/h). The demand rate is 8 m³/h in 5–7 h, 4.8 m³/h in 7–12 h and 10 m³/h in 17–19 h, all more than the inflow, so a balancing tank **is necessary**.


#### Mass-curve table (analytical method)
Inflow: 3.33 m³/h (daily demand spread over 24 h). Time is counted from the start of the first demand period; a positive cumulative value means surplus in the tank.

| Time | Demand (m³) | Inflow (m³) | Inflow − demand | Cumulative |
|---|---|---|---|---|
| 05:00–07:00 | 16.00 | 6.67 | -9.33 | -9.33 |
| 07:00–12:00 | 24.00 | 16.67 | -7.33 | -16.67 |
| 12:00–17:00 | 16.00 | 16.67 | +0.67 | -16.00 |
| 17:00–19:00 | 20.00 | 6.67 | -13.33 | -29.33 |
| 19:00–05:00 | 4.00 | 33.33 | +29.33 | 0.00 |

Total demand = 80.00 m³; total inflow = 80.00 m³.

#### Capacity
- Maximum cumulative surplus = 0.00 m³
- Maximum cumulative deficit = 29.33 m³
- Balancing capacity = max. surplus + max. deficit = 0.00 + 29.33 = **29.33 m³**

**Answer: A balancing tank is necessary; capacity ≈ 29.3 m³ (adopt 30 m³), provided the source shortage of 10.9 m³/day is made up.**

## Check yourself

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

1. How does the spring yield compare with demand?
   A. Yield 69.12 m3/day is less than the 80 m3/day demand
   B. Yield exceeds demand
   C. They are equal
   D. Yield is 0.8 m3/day
   Answer: A. 0.8 lps = 69.12 m3/day, a shortage of 10.88 m3/day that a tank cannot remove. (Key point: Source adequacy)

2. What inflow rate is used for balancing?
   A. 2.88 m3/h, the spring yield
   B. 3.33 m3/h, demand spread over 24 h
   C. 8 m3/h
   D. 5.33 m3/h
   Answer: B. 80/24 = 3.33 m3/h, because the shortage is assumed made up. (Key point: Inflow assumed)

3. What is the maximum cumulative deficit?
   A. 16.67 m3
   B. 29.33 m3
   C. 9.33 m3
   D. 13.33 m3
   Answer: B. After 17-19 h the cumulative reaches -29.33 m3. (Key point: Maximum deficit)

4. Since the max surplus is 0, what is the balancing capacity?
   A. 29.33 m3 (adopt 30 m3)
   B. 80 m3
   C. 10.88 m3
   D. 0 m3
   Answer: A. Capacity = 0 + 29.33 = 29.33 m3. (Key point: Capacity)

## Related in Water Supply Engineering

- [Is balancing tank necessary: 20000 L/day spring](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ares-k72) — Water Supply Engineering, chapter 7
- [Balancing reservoir: 500 population, spring 0.28 lps](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ares-a75) — Water Supply Engineering, chapter 7
- [Storage tank capacity and water level, 20000 L/day](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-level-river-20000) — Water Supply Engineering, chapter 7, asked 2×
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- [Is reservoir necessary: village of 800, spring 0.5 L/s](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ares-b81) — Water Supply Engineering, chapter 7

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