2. Introduction: Quantity ofWater
Why to study aboutQuantity ofWater?
Toestimate the water demand for the community
Todesign the water supply system with long term benefits
Todetermine the capacity of the reservoir used in water supply system
Tofind the suitable water resources that can meet the
demand.
3. 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.
4. Various Quantities need to be assessed
• Total annual volume (V) in liters or ML
• Annual average rate of draft in lit/day i.eV/365
• Annual avg. rate of draft in lit/day/person called per capita
demand
• Average rate of draft in lit/day per service i.e. (V/365) X (1/No.
of services)
• Fluctuations in flows expressed in terms of percentage ratios of
maximum or minimum yearly, monthly, daily or hourly rates to
their corresponding average values.
5. Factors to be known before Designing Water
Supply System
Population
PerCapita
Demand ofWater
Base and Design
period
6. Determining quantity of water
The quantity of water required for a city can be tackled by twofactors:
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 calculated.
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 forecastmethod.
7. 1. Domestic water demand
2. Industrial water demand
3. Institution and commercial water demand
4. Demand for public uses
5. Fire demand
6. Water required to compensate losses in wastes and thefts
Types of water demands
9. This includes the water requirement of people for drinking, cooking,
bathing, lawn sprinkling, gardening, sanitary purposes, etc.
The domestic consumption completely depends upon the economic
status of the people:
200 lit/head/day for rich living
135 lit/head/day for middle class living
•The total domestic demand is equal to 50-60% of the total water
consumption.
10. Use Consumption in litres per
head per day
Drinking 5
Cooking 5
Bathing 75
Washing clothes 25
Washing of utensils 15
Washing and cleaning of
houses and residences
15
Lawn watering and gardening 15
Flushing of water closets, etc. 45
TOTAL 200
11. Use Consumption in litres per
head per day
Drinking 5
Cooking 5
Bathing 55
Washing clothes 20
Washing of utensils 10
Washing and cleaning of houses
and residences
10
Flushing of water closets, etc. 30
TOTAL 135
Minimum Domestic water consumption for weaker sections and
LIG colonies in small Indian towns and cities
12. The quantity of industrial water demand will vary with the type and
number of industries.
In industrial cities the per capita water demand computed as 450
l/h/day for high scale industrial zones and as 50 l/h/day for small scale
industrial zones.
13. S. No. Name of industry
and product
Unit of production or
raw material used
Appropriate quantity of
water required per unit of
production or raw material
in kilo litres
1 Auto mobiles vehicle 40
2 Distillery (Alcohol) Kilo litre 122-170
3 Fertilizer Tonne 80-200
4 Leather (tanned) Tonne 40
5 Paper Tonne 200-400
6 Special quality paper Tonne 400-1000
7 Petroleum refinery Tonne 1-2
8 Steel Tonne 200-250
9 Sugar Tonne 1-2
10 Textile Tonne 80-140
14. The water requirements of institutions, hospitals, hotels,
restaurants, schools, offices, etc. come under this category.
The quantity will vary with the nature of the city and with the number
and type of commercial establishments.
On an average, a per capita demand of 20-50 l/h/day is usually
considered for such demand.
15. Indivisual water requirement
S.
No.
Type of Institution or Commercial establishment Avg demand in l/h/d
1 offices 45-90
2 Hostels 135-180
3 Restaurants 70 per seat
4 schools a) day school 45-90
b) Residential 135-225
5 Factories a) Where bath rooms are provided 45-90
b) No bath rooms provided 30-60
6 Hospitals ( Including laundry) a) beds less than 100 340 per bed
b) beds more than 100 450 per bed
7 Nurses homes & medical quarters 135-225
8 Cinema hall 15
9 Airports 70
10 Railway station 23-70
16. This includes the quantity
of water required for
public utility purposes,
such as
Watering of
public parks
Gardening
Washing and
sprinkling
on roads
Use in
public
fountains,
etc.
A figure of 10 l/h/day is
usually considered for this
demand.
17. PurposeWater
Public parks
Street washing
Sewer cleaning
Requirements
1.4 litres/m2/day
1.0-1.5 litres/m2/day
4.5 litres/head/day
The requirements of water for public utility shall be taken as…
18. In thickly populated and industrial areas, fires generally break out and
may lead to serious damages, if not controlled effectively.
There fore, a provision should be made in modern water supply
schemes for fighting fires.
The quantity of water for extinguishing fires, should be easily available
and kept always in storage reservoirs.
Fire demand
19. Kuichling’s formula:
Q = 3182 √𝑃
where, P = Population
Q = Quantity of water demand
Freeman’s formula:
10
Q = 1136 𝑃
+ 10
where, P = Population
Q = Quantity of water demand
20. National Board of Fire Under Writer’s formula
Population < 2,00,000
Q = 4637 sq.rt.(P)[1-0.01sq.rt.(p)]
Population > 2,00,000
Q = 54,600 l/min and more 9600 to
36400 l/min
21. Loses and wastes
• Losses due to defective pipe joints, cracked and broken
pipes, faulty valves and fittings.
• Losses due to, continuous wastage of water.
• Losses due to unauthorised and illegal connections.
• While estimating the total quantity of water of a town;
allowance of 15% of total quantity of water is made to
compensate for losses, thefts and wastage of water.
22. Water Consumption forVarious Purposes
Types of Normal Average %
Consumption Range
(lit/capita/da
y)
1 Domestic
Consumption 65-300 160 35
2 Industrial and
Commercial
Demand
45-450 135 30
3 Public Uses
including Fire
Demand
20-90 45 10
4 Losses and
Waste 45-150 62 25
38
23. Per Capita Demand ofWater
• Average quantity of water consumption or water demand for various
purposes per person per day
• Usually expressed in liters per capita per day(lpcd)
V
P ×365
• Per Capita demand in lpcd =
Where,
V= total quantity required per year in litres
P= population
It varies from person to person, place to place and time to time
• Water demands in liters/d= Per capita demand ×Population
24. Break up of Per Capita Demand for an Average Indian City
USE Demand in l/h/d
Domestic use 200
Industrial use 50
Commercial use 20
Civic use or public use 10
Wastes & thefts, etc 55
Total 335 = per capita Demand (q)
25. Factors affecting per capita demand
1. Size of the city: Per capita demand for big cities is generally
large as compared to that for smaller towns .
2. Presence of industries & commercial activities
3. Climatic conditions
4. Habits of people and their economic status
5. Pressure in the distribution system
6. Quality of water supplied
7. Development of sewerage facility
8. System of supply
9. Cost of water
10. policy of metering & Method of charging
26. 11. Quality of water: If water is aesthetically & medically
safe, the consumption will increase
12. Efficiency of water works administration: Leaks in
water mains and services; and unauthorized use of
water can be kept to a minimum by surveys.
13.Cost of water.
14. Policy of metering and charging method: Water tax
is charged in two different ways: on the basis of meter
reading and on the basis of certain fixed monthly rate.
27. FACTORE AFFECTINGTHEWATER DEMAND
Big city
• Size of the city
Small towns
Example: Delhi 244 l/c/d Vijayawada 135 l/c/d
• Climate condition
less in winter
more in summer
• Cost of water
rate demand rate demand
28. • Supply system
Bad Supply
• Distribution System
Good supply
demand
Pressure
high
Pressure
low
demand
demand demand
29. • Industry
• Quality of water
good demand demand
bad
demand demand
industry
industry
• Habit of people
EWS demand MIG demand
(Living style)
30. Variations in demand and its effects on design of components of
water supply scheme
• Variations in demand :
• Seasonal variation :
• Water Consumption :Winter , Summer, Rainy season
• DailyVariations
• Household & industrial activity.
• Water consumption – more holidays
• Hourly variations:
• Assessment of normal variations : to design supply pipes , service reservoirs , distributary
pipes etc..
31. Design Periods & Population Forecast
This quantity should be worked out with due provision for the
estimated requirements of the future .
The future period for which a provision is made in the water supply
scheme is known as the design period.
It is suggested that the construction of sewage treatment plant may
be carried out in phases with an initial design period ranging from 5
to 10 years excluding the construction period.
32. Design period is estimated based on the following:
•Useful life of the component, considering obsolescence, wear, tear, etc.
•Expandability aspect.
•Anticipated rate of growth of population, including industrial,
commercial developments & migration-immigration.
•Available resources.
•Performance of the system during initial period.
33.
34. Population forecasting
Design of water supply and sanitation scheme is based on the projected
population ofa particular city, estimated for the design period.
Any underestimated value will make system inadequate for the purpose
intended; similarly overestimated value will make it costly.
Changes in the population of the city over the years occur, and the system
should be designed taking into account of the population at the end of the
design period.
Factors affecting changes in population are:
increase due to births
decrease due to deaths
increase/ decrease due to migration
36. ARITHMETIC INCREASE METHOD
This method is suitable for large and old city with considerable development.
If it is used for small, average or comparatively new cities, it will give lower population
estimate than actual value.
In this method the average increase in population per decade is calculated from the past
census reports.
This increase is added to the present population to find out the population of the next
decade.Thus, it is assumed that the population is increasing at constantrate.
Hence, dP/dt = C i.e., rate of change of population with respect to time is constant.
Therefore, Population after nth decade will be Pn= Po+ n.x
Where, Pn is the population after ‘n’ decades and ‘P’ is present population
42. GRAPHICAL METHOD
In this method, the populations of last few decades are correctly
plotted to a suitable scale on graph. The population curve is
smoothly extended for getting future population. This extension
should be done carefully and it requires proper experience and
judgment. The best way of applying this method is to extend the
curve by comparing with population curve of some other similar
cities having the similar growth condition.
45. MASTER PLAN METHOD
• The big and metropolitan cities are generally not developed in haphazard
manner, but are planned and regulated by local bodies according to master
plan.
• The master plan is prepared for next 25 to 30 years for the city.
• According to the master plan the city is divided into various zones
such as residence, commerce and industry.
• The population densities are fixed for various zones in the master plan. From
this population density total water demand and wastewater generation for
that zone can be worked out. By this method it is very easy to access
precisely the design population.
46. LOGISTIC CURVE METHOD
• This method is used when the growth rate of population due to births,
deaths and migrations takes place under normal situation and it is not
subjected to any extraordinary changes like epidemic, war, earth quake or
any natural disaster, etc.,
• and the population follows the growth curve characteristics of living things
within limited space and economic opportunity.
• If the population of a city is plotted with respect to time, the curve so
obtained under normal condition looks like S-shaped curve and is known
as logistic curve.
