The 800 m^3 total demand includes losses. What is the first step?

Divide by 1.15 to get the net demand

How is the design-year population obtained from the net demand?

Subtract the non-domestic demands, then divide the domestic demand by 110 lpcd

Divide the net demand by 110 directly

Divide the other demands by 110

Multiply the domestic demand by 110

Asked 2/30
2073 Shrawan · 8 marks

Population in survey year from design demand 800 m3

Short answer

Work backwards from 800 m3/d including 15% losses: net demand 695652 l/d; non-domestic demand 250500 l/d, so domestic demand 445152 l/d at 110 lpcd gives design population 4047 in 2038. Back to 2016 at 1.9% for 22 years gives 2675.

Data obtained from a baseline survey of a newly formed municipality in year 2016 A.D are as follows. No. of day students in school = 2500, No. of big animals = 4000, No. of small animals = 6400. There are twenty offices, one hospital with 50 beds. The total water demand of municipality in design year with base period of 2 years and design period of 20 years is 800 $\mathrm{m^3}$ . The population growth rate of that community is 1.9% per annum. Determine the population in survey year.

This is a reverse problem: the total design demand is known, so the design population is found first and then brought back to the survey year.

Assumed rates: domestic 110 lpcd (municipality), day scholar 5 l/d, big animal 45 l/d, small animal 5 l/d, office staff 45 l/d (10 staff per office), hospital 340 l/bed/d, losses and wastage 15% of net demand. The total demand of 800 m $^3$ is taken per day, with losses included.

Step 1: demand other than domestic

Demand	Quantity	Rate	l/day
Day students	2,500	5	12,500
Big animals	4,000	45	180,000
Small animals	6,400	5	32,000
Offices (10 staff each)	200	45	9,000
Hospital (50 beds)	50	340	17,000
Other demands			250,500

Step 2: domestic demand in the design year

Net demand $= \dfrac{800{,}000}{1.15} = 695{,}652$ l/day

Domestic demand $= 695{,}652 - 250{,}500 = 445{,}152$ l/day

P_{2038} = \frac{445{,}152}{110} = 4{,}047

Step 3: population in the survey year

The design year is $2016+2+20 = 2038$ , so $n = 22$ years.

P_{2038} = P_{2016}(1+r)^{n} \Rightarrow P_{2016} = \frac{4{,}047}{(1.019)^{22}} = 2{,}675

Answer: Population in the survey year (2016) = 2,675 (about 2,670); design year population = 4,047.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Population in survey year from design demand 800 m3

Step 1: demand other than domestic

Step 2: domestic demand in the design year

Step 3: population in the survey year

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