---
title: "Design demand 2025, geometric method, rural village"
subject: "Water Supply Engineering"
chapter: 3
key: "semester_5/water_supply_engineering:demand-b66"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/demand-b66
site: BCT Engineering
---

# Design demand 2025, geometric method, rural village

Water Supply Engineering · Chapter 3: Quantity of Water

- Asked in: 2066 Bhadra (old course)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/demand-b66
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-3

## Question

Calculate the design water demand for the year 2025 for a rural village of Nepal. Use geometrical method for population forecasting. Census population is:

| Year | 1961 | 1971 | 1981 | 1991 | 2001 |
|---|---|---|---|---|---|
| Population | 8500 | 10050 | 14000 | 18400 | 22800 |

Take 1 school with 80 boarders and 300 day scholars. Consider live stock demand also.

## Short answer

Population in 2025 by geometric method: 41,214. Design water demand: 2,399 m3/day (27.8 l/s) including domestic, school, livestock, and 15% losses.

## Answer

The last census is 2001, so for 2025, $n = 2.4$ decades.

#### Population by geometrical increase method
**Geometrical increase method**

Average growth rate per decade (geometric mean): $r = \left(\dfrac{22{,}800}{8{,}500}\right)^{1/4}-1 = 27.976\%$

$$
P_{2025} = P_n(1+r)^n = 22{,}800\times(1+0.27976)^{2.4} = 41{,}214
$$


#### Water demand
**Design values assumed** (Nepal rural water supply practice): domestic 45 lpcd (public taps); day scholar 5 l/d; boarder 45 l/d; office staff 45 l/d with 10 staff per office; big animal (cow, buffalo) 45 l/d; small animal (goat, pig) 5 l/d; poultry 0.2 l/d; health post 1000 l/d; tea shop 500 l/d; losses and wastage 15% of net demand; maximum day factor 1.5 and peak hour factor 3. The number of animals is not given, so I assume one big animal per 10 persons and one small animal per 5 persons of the design population. Fire demand is neglected.

| Demand | Quantity | Rate | Demand (l/day) |
|---|---|---|---|
| Domestic (45 lpcd) | 41,214 | 45 l/c/d | 1,854,628 |
| Boarders | 80 | 45 l/c/d | 3,600 |
| Day scholars | 300 | 5 l/c/d | 1,500 |
| Big animals (1 per 10 persons) | 4,121 | 45 l/d | 185,463 |
| Small animals (1 per 5 persons) | 8,243 | 5 l/d | 41,214 |
| **Net demand** | | | **2,086,405** |

Losses and wastage $= 15\%$ of net demand $= 312{,}961$ l/day

$$
Q_{avg} = 2{,}086{,}405 + 312{,}961 = 2{,}399{,}366\ \text{l/day} = 2{,}399.37\ \mathrm{m^3/day} = 27.77\ \text{l/s}
$$

**Answer: Population in 2025 = 41,214; design water demand = 2,399 m$^3$/day (27.8 l/s).**

## Check yourself

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

1. For 2025 with last census 2001, n is
   A. 24 decades
   B. 2.4 decades
   C. 2.0 decades
   D. 0.24 decades
   Answer: B. (2025-2001)/10 = 2.4. (Key point: Value of n)

2. Which school demand is used for 80 boarders and 300 day scholars?
   A. 80 x 5 + 300 x 45
   B. 380 x 45
   C. 80 x 45 + 300 x 5 = 5,100 l/day
   D. 380 x 5
   Answer: C. Boarders use 45 l/d and day scholars 5 l/d. (Key point: School demand)

## Related in Water Supply Engineering

- [Population forecast 2021 census, 2024 base year](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apop-b81) — Water Supply Engineering, chapter 3
- [Rural village demand, survey 2070 BS, base year 2073](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ademand-as70) — Water Supply Engineering, chapter 3
- [Rural village demand for 2092 BS, incremental method](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ademand-k78) — Water Supply Engineering, chapter 3
- [Population forecast to 2040, geometric method](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apop-bk81) — Water Supply Engineering, chapter 3
- [Population 2088 by three methods, design year demand](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apop-k72) — Water Supply Engineering, chapter 3
- [Rural area demand 2025 AD, incremental increase](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ademand-bk68) — Water Supply Engineering, chapter 3

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