This presentation discusses water demand and population forecasting methods. It defines water demand as the rate of water required for a town or city to carry out daily activities. There are different types of water demand including domestic, industrial, institutional, and fire demand. Population is a key factor in determining water demand, and there are several methods discussed for forecasting future population, including arithmetical increase, geometrical increase, and incremental increase methods. The presentation provides details on each of these population forecasting techniques.

1. PRESENTATION ON:
WATER DEMAND.

2. PRESENTED BY:
 SHAIKH MOHD. AMIR N. 150860106062
 PRAJAPATI RIYA P. 150860106054
 BHANDARI NEENAD H. 150860106006
 RATHOD NEHA M. 150860106055

3. Content
o Water demand
o Determining quantity of water
o Types of water demand
o Factors affecting water demand
o Population forecasting method
o Types of population forecasting methid

4. Water Demand
 The rate of water required for a particular town or a
city to successfully carry out its day to day activities is
known as water demand.
While designing the water supply scheme for a town
or city, it is necessary to determine the total quantity
of water required. As a matter it is a first duty of an
engineer to determine water demand and then to find
a probable source from where the demand can be met.

5. Determining quantity of water
The quantity of water required for a city can be tackled
by two factors:
1. Rate of demand: The requirements of water for
various uses are properly analyzed and ultimately,
the rate of consumption per capita per day is worked
out.
2. Population: The population to be served by the
water supply scheme is estimated and estimate of
future population is worked out with help of
population forecast method.

6. Types of water demand
The types of water demand of a city or a town:
Domestic water demand
Industrial water demand
Institutional and commercial water demand
Demand for public uses
Fire demand
Compensate losses demand

7. Factors affecting water demand
Following are the main factors that affect water demand
1. Size of the city
2. Living standard of the people
3. Climatic conditions
4. Quality of water
5. Industrial and commercial activities
6. Pressure in the distribution system
7. System of sanitation
8. Cost of water
9. System of supply
10. Metering and method of charging

8. Population forecasting method
 Two types of population estimates are needed for the
operation and the design of the water supply
i. Short term estimates in the range 1-10 years
ii. Long term estimates in the range 10-50 years or
more.
 The population is increased by births, decreased by
deaths, increased by migration and increased by
annexation.

9. Types of population forecasting methods
1. Arithmetical increase method
2. Geometrical increase method
3. Incremental increase method
4. Decreasing rate of growth method
5. Simple graphical method
6. Comparative graphical method
7. Zoning method or master plan method

10. Arithmetical increase
method
 This is the most simple method of
population forecast and is based on the
assumption that the population is
increasing from decade to decade at a
constant rate.
 dp/dt = C
Where,
dp/dt is the rate of change of population.
 The population at the end on ‘n’ decades
is given by:
Pn= P + ni
Where,
Pn = population after ‘n’ decades.
P = Present population
i = average increase per decade
n = number of decades
Geometrical increase
method
 In this method it is assumed that the
percentage increase in population from
decade to decade is constant. From the
population data of previous three to four
decades, the percentage increase on
population is found and its average is
found.
 The population at the end on ‘n’ decades
is given by:
Pn= P [1+(r/100)]n
Where,
Pn = population after ‘n’ decades.
P = Present population
r = average incremental increase
n = number of decades

11. Incremental
Increase method
 The average increase in
population is determined by
the arithmetical increase
method and to this as added
the average of the net
incremental increase once for
each future decade.
 The population at the end on ‘n’
decades is given by:
Pn = P + ni + [{n(n+1)r}/2]
Where,
Pn = population after ‘n’ decades.
P = Present population
i = average increase per decade
r = average incremental increase
n = number of decades
Decreasing rate of
growth method
 In this method, the average
decrease in the percentage
increase is worked out , and is
then subtracted from the least
percentage increase for each
successive decades.
Simple graphical method
 In this method, a curve is
plotted between the population
p and time T, with the help of of
census data of previous few
decades. The curve is smoothly
extended to forecast the future
population.

12. Graphical comparison method
 In this method, the cities having conditions and
characteristics similar to the city whose future population
is to be determined are first of all selected. It is then
assumed that the city under consideration will develop as
the selected similar cities have developed in the past.
Zoning method or master plan method
 The city and town are divided into various zones such as
commercial, industrial, residential etc. The future
expansion of cities is strictly regulated by various bye-laws
of corporation and other local bodies.
 The population of a particular zone is fixed and according
to that the water supply schemes are designed.

13. Thank you…