---
title: "Rural village demand for 2092 BS, incremental method"
subject: "Water Supply Engineering"
chapter: 3
key: "semester_5/water_supply_engineering:demand-k78"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/demand-k78
site: BCT Engineering
---

# Rural village demand for 2092 BS, incremental method

Water Supply Engineering · Chapter 3: Quantity of Water

- Asked in: 2078 Kartik, 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/demand-k78
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-3

## Question

Estimate the total water requirement for a rural village for the year 2092 BS by forecasting the population by incremental increase method with the following census data.

| Year (BS) | 2018 | 2028 | 2038 | 2048 | 2058 | 2068 |
|---|---|---|---|---|---|---|
| Population | 7200 | 8100 | 9300 | 11000 | 13000 | 16000 |

There are 3 schools (350 day and 50 boarder scholars), livestock (5000 chickens, 1500 goats and 60 cows), 2 health posts with 10 beds capacity and other offices with 100 staffs altogether. Neglect the fire demand for rural area.

## Short answer

Use incremental increase over 2.4 decades: design population in 2092 is 22,366. With domestic 45 lpcd and given institutional, livestock, and 15% losses, total water requirement is 1,181 m3/day, about 13.7 l/s.

## Answer

The design year is 2092 BS. The last census is 2068, so $n = (2092-2068)/10 = 2.4$ decades.

#### Population by incremental increase method
Increase per decade: 900, 1,200, 1,700, 2,000, 3,000; incremental increase: 300, 500, 300, 1,000.
$\bar x = 1{,}760.00$, $\bar y = 525.00$

$$
P_{2092} = P_n + n\bar x + \frac{n(n+1)}{2}\bar y = 16{,}000 + 2.4(1{,}760.00) + \frac{2.4(3.4)}{2}(525.00) = 22{,}366
$$


#### 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; big animal (cow, buffalo) 45 l/d; small animal (goat, pig) 5 l/d; poultry 0.2 l/d; losses and wastage 15% of net demand. Health post beds are taken at 100 l/bed/day. The 3 schools have 350 day scholars and 50 boarders in total, and the 2 health posts have 10 beds in total. Fire demand is neglected.

| Demand | Quantity | Rate | Demand (l/day) |
|---|---|---|---|
| Domestic (45 lpcd) | 22,366 | 45 l/c/d | 1,006,470 |
| Day scholars | 350 | 5 l/c/d | 1,750 |
| Boarders | 50 | 45 l/c/d | 2,250 |
| Chickens | 5,000 | 0.2 l/d | 1,000 |
| Goats | 1,500 | 5 l/d | 7,500 |
| Cows | 60 | 45 l/d | 2,700 |
| Health posts (10 beds in total) | 10 | 100 l/bed/d | 1,000 |
| Office staff | 100 | 45 l/staff | 4,500 |
| **Net demand** | | | **1,027,170** |

Losses and wastage $= 15\%$ of net demand $= 154{,}076$ l/day

$$
Q_{avg} = 1{,}027{,}170 + 154{,}076 = 1{,}181{,}246\ \text{l/day} = 1{,}181.25\ \mathrm{m^3/day} = 13.67\ \text{l/s}
$$

**Answer: Design population (2092 BS) = 22,366; total water requirement = 1,181 m$^3$/day (13.7 l/s).**

## Check yourself

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

1. Design year 2092 BS with last census 2068: n?
   A. 2.4 decades
   B. 24 decades
   C. 3.4 decades
   D. 2.0 decades
   Answer: A. (2092-2068)/10 = 2.4. (Key point: n value)

2. Which formula gives the population?
   A. Pn + n x
   B. Pn(1+r)^n
   C. Pn + n x + n(n+1)/2 y, with x = 1,760 and y = 525
   D. Pn + 2.4 x 525
   Answer: C. This is the incremental increase method result, 22,366. (Key point: Incremental formula)

3. Which component dominates the net demand?
   A. Livestock
   B. Schools
   C. Health posts
   D. Domestic demand at 45 lpcd (1,006,470 l/day)
   Answer: D. Domestic demand of 22,366 x 45 = 1,006,470 l/day is almost all of the net 1,027,170 l/day. (Key point: Largest component)

4. How are losses added?
   A. 15% of net demand added
   B. Subtracted from net demand
   C. Added only to domestic
   D. Not added in rural
   Answer: A. 15% of 1,027,170 = 154,076 l/day added, giving 1,181,246 l/day. (Key point: Losses)

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