Rural village demand for 2092 BS, incremental method

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.

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).