This document discusses water consumption rates and factors that affect demand. It provides the following information: 1. Domestic use accounts for 35% of water consumption on average at 160 liters/person/day. Industrial and commercial use accounts for 30% at 135 liters/person/day. 2. Total average daily consumption is estimated at 270 liters/person/day. Peak demand is estimated to be 2.7 times the average daily rate. 3. Fire demand is calculated using various formulas that take population size into account. The rate of fire demand is very high even if total volume is low.

1. LECTURE NO.9-10

2. WATER CONSUMPTION RATE
 It is very difficult to precisely assess the quantity of
water demanded by the public, since there are many
variable factors affecting water consumption. The
various types of water demands, which a city may have,
may be broken into following classes:

3. Types of
Consumption
Normal
Range
(lit/capita
/day)
Avera
ge
%
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
WATER CONSUMPTION RATE

4. WATER CONSUMPTION RATE
 Domestic purpose
 Industrial use
 Public use
 Fire demand
 Losses, Wastage and
thefts
Total
135 l/capita/day
40 l/capita/day
25 l/capita/day
15 l/capita/day
55 l/capita/day
270 l/capita/day

5. FIRE DEMAND
 The per capita fire demand is very less on an average
basis but the rate at which the water is required is very
large. The rate of fire demand is sometimes treated as
a function of population .

6. FIRE DEMAND
Authority Formulae (P in thousand) Q for 1 lakh
Population)
1
American Insurance
Association
Q (L/min)=4637 P (1-0.01 P) 41760
2
Kuchling's Formula Q (L/min)=3182 P 31800
3
Freeman's Formula Q (L/min)= 1136.5(P/5+10) 35050
4
Ministry of Urban
Development Manual
Formula
Q (kilo liters/d)=100 P for P>50000 31623

7. LOSSES AND WASTES
 All the water which goes into the distribution pipes does
not reach the consumers because of the following reasons:
 Losses due to defective pipe joints, cracked and broken
pipes, faulty valves and fittings.
 Losses due to consumers keep open their taps even when
they are not using the water and allow the continuous
wastage of water
 Losses due to unauthorized 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

8. AVERAGE DAILY PER CAPITA DEMAND
 Average Daily Per Capita Demand
= Quantity Required in 12 Months/ (365 x
Population)
= Q/(365xP)
 If this average demand is supplied at all the times, it will
not be sufficient to meet the fluctuations.
 Per capita demand of the town depends on various factors
like standard of living, number and type of commercial
places in a town.

9. FLUCTUATIONS IN THE RATE OF
DEMAND
 Seasonal variation: The demand peaks during summer.
Firebreak outs are generally more in summer, increasing
demand. So, there is seasonal variation .
 Daily variation: This demand depends on the activity. People
draw out more water on Sundays and Festival days, thus
increasing demand on these days.
 Hourly variations are very important as they have a wide range.
During active household working hours i.e. from six to ten in the
morning and four to eight in the evening, the bulk of the daily
requirement is taken. During other hours the requirement is
negligible. Moreover, if a fire breaks out, a huge quantity of water
is required to be supplied during short duration, necessitating
the need for a maximum rate of hourly supply.

10. FLUCTUATIONS IN THE RATE OF
DEMAND
 Adequate quantity of water must be available to
meet the peak demand. To meet all the
fluctuations, the supply pipes, service reservoirs
and distribution pipes must be properly
proportioned. The water is supplied by pumping
directly and the pumps and distribution system
must be designed to meet the peak demand. The
effect of monthly variation influences the design
of storage reservoirs and the hourly variations
influences the design of pumps and service
reservoirs. As the population decreases, the
fluctuation rate increases.

11. GOODRICH FORMULA
 Estimates maximum demand (expressed as daily water
demand based on time period for which maximum
water demand is desired) for community when given
annual average per capita daily water use rate:
p= 180. t -0.10
 where p = percentage of average annual rate
(volume/day) used in period of time of interest
t = length of period for which peak demand is
required (days) (valid time period 2 hrs. to 360
days)

12. PEAKING FACTORS
 Water use varies with the time of year and the time of
day. To account for these variations, peaking factors
are commonly used in evaluating water system
operating characteristics. Peaking factors are
multipliers that are applied to the average day demand
to approximate other peak water demands. Peaking
factors are often estimated because of the lack of
detailed water use data. Peak water demands and
associated peaking factors are important in evaluating
water system

13. PEAKING FACTORS
 Peaking factors are applied to the Average Daily
Demand (ADD)to estimate the other peak demands.
 The maximum day demand (MDD) is the highest daily
water use rate during the year. The MDD peaking
factor is the ratio of MDD to ADD.
 The maximum hour demand (MHD) is the highest
hourly water use rate during the year. The MHD
peaking factor is the ratio of MHD to ADD. This factor
is usually estimated based on engineering judgment,
since it is difficult to determine the actual maximum
hour demand in the system.

14. MAXIMUM DAILY DEMAND
 Maximum daily consumption is taken as 180% of the
average daily consumption
 Maximum daily demand = 1.8 x average daily demand
 Consumption rate for max week = 148% of the annual
average daily consumption
 Consumption rate for max month = 128% of the annual
average daily consumption

15. PEAK DEMAND
 The maximum hourly consumption is likely to be about
150% of the average of that day or maximum day or 270% of
the annual average daily consumption
 Maximum hourly demand of maximum day i.e. Peak
demand
= 1.5 x average hourly demand
= 1.5 x Maximum daily demand/24
= 1.5 x (1.8 x average daily demand)/24
= 2.7 x average daily demand/24
= 2.7 x annual average hourly demand


16. DESIGN PERIODS
 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.
 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.

17. DESIGN PERIODS
COMPONENTS DESIGN PERIODS
Storage by Dams 50 years
Wells 5 years
Pipe lines from the source 25 years or more
Water Treatment Plant 10-15 years
Pumping plant
(1) Pump house 30 years
(2) Electric motors and pumps 10 -15 years
Distribution system 30 years

18. DESIGN REQUIREMENTS
 Filters and pumps are designed for 1.50 to 2 times the average
daily demand.
 Pipe mains are designed for the maximum daily demand.
 Intake structures are designed for maximum daily demand
 Treatment plants are designed for the maximum daily
demand.
 Distribution system is designed for the maximum hourly
flow including fire demand

19. SURFACE WATER SOURCES
NATURAL PONDS AND LAKES
 In mountains at some places natural basin’s are formed
with impervious bed by springs and streams are known as
“lakes”. The quality of water in the natural ponds and lakes
depends upon the basin’s capacity, catchment area, annual
rainfall, porosity of ground etc. But lakes and ponds
situated at higher altitudes contain almost pure water
which can be used without any treatment. But ponds
formed due to construction of houses, road, railways
contains large amount of impurities and therefore cannot
be used for water supply purposes.

20. SURFACE WATER SOURCES
STREAMS AND RIVERS
Rivers and streams are the main source of surface source of water. In summer ,
quality of river water is better than m0nsoon because in rainy season the run-
off water also carries clay, sand, silt etc. .which make the water turbid. So river
and stream water require special treatments. Some rivers are snow fed and
perennial and have water throughout the year and therefore they do not require
any arrangements to hold the water. But some rivers dry up wholly or partially
in summer. So they require special arrangements to meet the water demand
during hot weather. Mostly all the cities are situated near the rivers discharge
their used water of sewage in the rivers, therefore much care should be taken
while drawing water from the river.

21. SURFACE WATER SOURCES
 IMPOUNDING RESERVOIRS
 In some rivers the flow becomes very small and cannot meet the requirements
of hot weather. In such cases, the water can be stored by constructing a bund, a
weir or a dam across the river at such places where minimum area of land is
submerged in the water and max. quantity of water to be stored. In lakes and
reservoirs, suspended impurities settle down in the bottom, but in their beds
algae, weeds, vegetable and organic growth takes place which produce bad
smell, taste and colour in water. Therefore this water should be used after
purification. When water is stored for long time in reservoirs it should be
aerated and chlorinated to kill the microscopic organisms which are born in
water.

22. INTAKES FOR COLLECTING
SURFACE WATER:
 The main function of the intakes works is to collect
water from the surface source and then discharge
water so collected, by means of pumps or directly to
the treatment plant. Intakes are structures which
essentially consists of opening, grating or strainer
through which the raw water from river, canal or
reservoir enters and carried to the sump well by means
of conduits water from the sump well is pumped
through the rising mains to the treatment plant.

23. INTAKES FOR COLLECTING
SURFACE WATER
The following points should be kept in mind while selecting a site for intake works.
 Where the best quality of water available so that water is purified economically in
less time.
 At site there should not be heavy current of water, which may damage the intake
structure.
 The intake can draw sufficient quantity of water even in the worst condition, when
the discharge of the source is minimum.
 The site of the work should be easily approachable without any obstruction
 The site should not be located in navigation channels
 The intake should be near the treatment plant so that conveyance cost is reduced from
source to the water works
 The intake should not be located in the vicinity of the point of sewage disposal for
avoiding the pollution of water.
 At the site sufficient quantity should be available for the future expansion of the
water-works.

24. TYPES OF INTAKE STRUCTURES
 Depending upon the source of water the intake works
are classified as following
 Lake Intake
 Reservoir Intake
 River Intake
 Canal Intake

25. LAKE INTAKE
 For obtaining water from lakes mostly submersible
intakes are used. These intakes are constructed in the
bed of the lake below the water level; so as to draw
water in dry season also. These intakes have so many
advantages such as no obstruction to the navigation,
no danger from the floating bodies and no trouble due
to ice. As these intakes draw small quantity of water,
these are not used in big water supply schemes or on
rivers or reservoirs. The main reason being that they
are not easily approachable for maintenance.

27. RIVER INTAKES
 Water from the rivers is always drawn from the
upstream side, because it is free from the
contamination caused by the disposal of sewage in it.
It is circular masonary tower of 4 to 7 m in diameter
constructed along the bank of the river at such place
from where required quantity of water can be obtained
even in the dry period. The water enters in the lower
portion of the intake known as sump well from
penstocks.

29. RESERVOIR INTAKE
 It consists of an intake well, which is placed near the
dam and connected to the top of dam by foot bridge.
The intake pipes are located at different levels with
common vertical pipe. The valves of intake pipes are
operated from the top and they are installed in a valve
room. Each intake pipe is provided with bell mouth
entry with perforations of fine screen on its surface.
The outlet pipe is taken out through the body of dam.
The outlet pipe should be suitably supported. The
location of intake pipes at different levels ensures
supply of water from a level lower than the surface
level of water.

31. CANAL INTAKE
 The intake chamber is constructed in the canal
section. This results in the reduction of water way
which increases the velocity of flow. It therefore
becomes necessary to provide pitching on the
downstream and upstream portion of canal intake.
The entry of water in the intake chamber takes
through coarse screen and the top of outlet pipe is
provided with fine screen. The inlet to outlet pipe is of
bell-mouth shape with perforations of the fine screen
on its surface. The outlet valve is operated from the top
and it controls the entry of water into the outlet pipe
from where it is taken to thetreatment plant.

33. RESERVOIRS
 Reservoirs are structures that store water.
 In general, we observe high flow in winter and low flow in
summer, and very high values in spring months or
snowmelt seasons in Northern Hemisphere. On the other
hand, the water demand is high in summer and low in
winter .Therefore, the regulation of the stream flow is
required meet the demands.
 This regulation is possible by constructing reservoirs in
the stream.

34. IMPORTANT DEFINITIONS
 NORMAL POOL LEVEL
It is the maximum elevation to which the reservoir
surface will rise during ordinary operating conditions
 MINIMUM POOL LEVEL
It is the lowest elevation to which pool is to be drawn
under normal conditions
 USEFUL STORAGE
The storage volume is between minimum and normal
pool level

35. IMPORTANT DEFINITIONS
 DEAD STORAGE
Water held below minimum pool level is dead storage
 SURCHARGE STORAGE
It is normally uncontrolled i.e. it exists only while
flood is occurring and it cannot be retained for later
use.
 VALLEY STORAGE
The volume of water in a natural stream channel at
any instant

36. IMPORTANT DEFINITIONS
 SAFE YIELD (FIRM YIELD)
The amount of water that is supplied for a critical
period. It is a guarantied amount during the critical
period
 CRITICAL PERIOD:
The duration of lowest flow observed in the records of
the stream.
 SECONDARY YIELD
During the periods of high flow there will be extra
available water, more than the safe yield which is called
secondary yield

37.  AVERAGE YIELD: The arithmetic average of the safe
and secondary yields over a long period.
 TARGET YIELD: The yield determined based on the
estimated demands for a reservoir.

39. PURPOSES OF CONSTRUCTING
RESERVOIRS
 There are number of purposes of constructing reservoirs
 Irrigation,
 Sediment accumulation,
 Transportation,
 Electricity generation,
 Water supply (municipal and industrial)
 Flood control, and
 Recreational.
They are also used to supply emergency water like fire
fighting or stabilize pressures in the network.

40. RESERVOIRS
 When the total supply of water (ΣS) is sufficient to
meet the total demand (ΣD) during a specified period
of time, the water storage is required when S<D.