water supply and Treatment (2).pptx

Water Supply & Treatment
Tutorial class for HWRE
GC students
January 2023

Course Objectives
◦ Learning objectives can be formulated as:
🞄 The objective of this course is to give students a broad
understanding of population forecasting, water demand, water
source, collection, and distribution of water.
🞄The general idea about water supply and water treatment
techniques

1.QUANTITY OF WATER
 Introduction
 In the design of any water work projects, it is
necessary to estimate the amount of water that is required.
This involves:
served
– Determination of people who will be
– per capita water consumption
– Analysis of the factors

1.2 Types of demands
 Various Types of Demands
 Domestic water demand
 Industrial and commercial water demand
 Demand for public use
 Fire demand
 Water required to compensate losses in wastes

Water Demand
Domestic water demand
• This includes the water required in private buildings for
drinking, cooking, bathing, gardening, sanitary purposes, etc.
• The total domestic consumption generally amounts to 55 to 60%
of the total water consumption.
Industrial & commercial water demand
• This includes the quantity of water required to be supplied to
offices, factories, different industries, big hotels, hospitals, etc.
20 to 25% of the total water consumption.

Water Demand
 Demand for public use
• This includes the quantity of water required for public
utility purposes, such as watering of public parks,
gardening, washing and sprinkling on the roads, use in
public fountains and etc.
 Fire demand
• The quantity of water required to fight fire. There are
formulas to estimate Fire demand ,

a. National board of fire underwriter formulas.
Q = 64 √ P (1 – 0.01√P)
Where Q = rate of flow of water in l/sec
P = Population in thousand
b. Freeman formula.
Q = 1135.5 ((P⁄ 10) + 10)
Where Q is in lit/min
c.Kuichling formula.
Q = 3182 √P
Where Q is in lit / min
P is in thousands
Fire demand cont.…

Water Demand
 Water required to compensate losses in
wastes
– this includes the water lost in leakage due to
bad plumbing or damage meters, stolen water
due to unauthorized water connections and
other losses.
– Generally ,allowance of 15 – 20% of total quantity of water is
made to compensate for the losses.

Factors Affecting Water Demand
o Size of the city
o Climatic condition
o Characteristics of population
o Quality of water supplies
o Pressure in distribution system
o Cost of water
o System of supply
o Policy of metering and method of charging

Factors Affecting water demand
 Size of City
The per capita water demand of the town, will
increase with the size of the town, because more
water will be required in street washing, running of
sewers, maintenance of parks and gardens
 Climatic condition
The quantity of water required in hotter and dry
places is more due to use sprinkling of water in
garden, washing of clothes and bathing.

Factors Affecting Water Demand
 Living standard of the people
The per capita demand of the town increase with the
standard of living of the people. The people will start using
room coolers, use of flush latrines, use of automatic dish
washing and others.
 pressure in the distribution system
the rate of water consumption increases with the increase in
the pressure of the distribution system. The water reaches the
upper storey of the building only if it is released with the
required pressure.
If the pressure ⭡- more water loss due to leakage, wastage

Variation in rate of consumption
 Per capita demand: means the annual consumption of water. It was
therefore, defined as the annual average daily consumption per
person.
per capita Demand = Q / P*365
Where Q: – is the total quantity of water required by a town per
year in liter.
P: - The population of the town
 seasonal variation:
Large amount of water uses in summer season, and lesser user in winter.

Design Period and Population
Forecasting
 Design period
 The number of years for which the designs of water
works have been done is known as design period.
These period should neither be too short or too long.
 Mostly water works are designed for design period of
20 – 30 years.

Factor, which should be kept in view while fixing
the design period:
 Fund
 The life of the material used in project (pipes,
structural materials )
 Anticipated expansion of the town
 The rate of interest on the loan taken

Population Forecasting
 When the design period is fixed the next step is to
determine the population in various periods, because
the population of the towns generally goes on
increasing.
 There are three major factors which affect change in
population:
– Birth
– Death
– Migration

Population forecasting
 Methods of population forecasting
 Arithmetical increase method
 Geometrical increase method
 Incremental increase method
 Decreasing rate method
 Logistic Curve method
 Simple graphical method
 Master plan method
 CSA method

Arithmetical increase method
Pn = Po + nK
Where; Pn = population at n decades or years
Po = present/initial population at the base year
n = decade or year
K= arithmetic increase
This method is generally applicable to large and old cities.

o Geometrical increase method
⚫ In this method it is assumed that the percentage increase in
population from decade to decade remains constant.
⚫ If the present population is Po and average percentage growth is
k, the population at the end of n decade will be:
Pn = po (1 + k)n
where po = initial population ,Pn = popn at n decades ,n = Decades &
k = Percentage (geometric) increase
 This method is mostly applicable for growing towns and cities having vast
scope of expansion.

 Incremental increase method
This method is the combination of the above two methods
and, therefore gives the advantages of both arithmetic and
geometric increase methods and gives satisfactory results.
Decreasing rate method
 In this method, the average decrease in the percentage
increase is worked out and is then subtracted from the late
percentage increase for each successive decades.
 This method is applicable to average size cities growing
under normal condition

Logistic Curve method
When the population of a town is plotted
with respect time the curve so obtained
under normal condition is s – shaped
curve and is known as logistic curve.

CSA method
Pn  Po * e kn
Where,
Pn = population at n decades or years
Po = initial population
n = decade or year
k = growth rate in percentage
Is a Method used by the Ethiopian statistic Authority
for population forecasting

Water Sources
 Sources of Water Supply
– The origin of all water is rainfall
– Water can be collected
 as it falls
 as rain before it reaches the ground
 as surface water when it flows over the ground
 as ground water when it percolates in to the ground

Water Sources
 All the sources of water can be broadly
divided into:
– Surfaces sources and
– Sub surface sources
 Surfaces Sources
The surface sources further divided into
– Streams and rivers
– Ponds and Lakes
– Impounding reservoirs etc.

 Subsurface Sources
These are further divided into
– Infiltration galleries
– Infiltration wells
– Springs
 Gravity Springs
 Surface Spring
 Artesian Spring
– Wells

Water Sources
 Wells
– A well is defined as an artificial hole or pit made in
the ground for the purpose of tapping water
– types of wells
 Shallow wells
 Deep wells
 Tube wells
 Artesian wells

Intakes for Collecting Surface Water
 The main function of the intakes works is to
collect water from the surface source
 Intakes are structures which essentially
consist of opening, grating or strainer
through which the raw water from river, canal
or reservoir enters

Intakes for Collecting Surface Water
 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
–

Lake Intake
 These intakes are constructed in the bed of
the lake below the water level; so as to draw
water in dry season also

River Intake
 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

Reservoir Intake
 It consists of an intake well, which is placed
near the dam and connected to the top of
dam by Foot Bridge

Canal Intake
 An intake chamber is constructed in the
canal section

Water Sources Selection Criteria
 Location: The sources of water should be as near as to
the town as possible.
 Quantity of water: the source of water should have
sufficient quantity of water to meet up all the water
demand through out the design period.
 Quality of water: The quality of water should be good
which can be easily and cheaply treated.
 Cost: The cost of the units of the water supply schemes
should be minimum.

Water quality and pollution
 Absolutely pure water is never found in
nature and contains number of impurities in
varying amounts
 The rainwater which is originally pure also
absorbs various gases, dust and other
impurities while falling
 The water supplied to the public should be
strictly according to the standards laid down
from time to time

Water Quality Characteristics
 impurities present in water may be divided
into the following three categories
– Physical Characteristics
– Chemical Characteristics
– Biological Characteristics

 Physical characteristics
– Turbidity
– Color
– Taste and odor
– Temperature

 Chemical characteristics
– Total solids
– Alkalinity
– pH
– Dissolved oxygen
– BOD, COD
– Nitrogen
– Hardness (calcium & Magnesium)

 biological characteristics
– Bacterium
– Viruses
– Algae
– protozoa

Water quality standards
Parameter WHO guideline Recommended for
Ethiopia
pH 6.5-8.5 5.0-9.5
Total solids, mg/L 1000 2000
Total hardness, mg/L 500 600
Chloride, mg/L 250 800
Sulphate, mg/L 400 600
Fluoride, mg/L 1.5 4
Iron, mg/L 0.3 3
E. Coli, MPN/100 ml 10 30
Nitrate , mg/L 10 40

Sources of Water Pollution
 Following are the main sources of water
pollution.
– Domestic sewage
– Industrial wastes
– Agricultural areas
– Distribution system

WATER TREATMENT
 The process of removing the impurities from
water is called water treatment and the
treated water is called wholesome water
 The surface sources generally contains large
amount of impurities therefore they requires
sedimentation, filtration and chlorination as
treatment
 Groundwater which is usually clear may
require only disinfection

Water Treatment
 Methods of Water Treatment
– Aeration
– Screening and grit removal
– Plain sedimentation
– Coagulation and flocculation
– Secondary sedimentation
– Filtration
– Adsorption
– Softening
– Disinfections

Aeration
 It is the process of bringing water in intimate
contact with air, while doing so water
absorbs oxygen from the air
 Aeration may be used to remove undesirable
gases dissolved in water i.e. Co2, H2S,
 Different types of aerators are available
– Gravity Aerator
– Spray aerator
– Air diffuser
– Mechanical Aerator

Aerators
 Gravity aerators
A. Cascade towers
Inlet
chamber
Collection
Chamber

Aerators
B. Inclined apron possibly shaded with plates
Inlet chamber
Collection
Chamber

Aerators
C. Tray aerator
– In tray aerator water falls through a series of trays
perforated with small holes, 5 - 12mm diameter
and 25 - 75mm spacing center to center

Aerators
 Spray aerators
– spray droplets of water into the air from stationary or
moving orifices or nozzles
– Water is pumped through pressure nozzles to spray in
the open air as in fountain to a height of about 2.5m

Aerators
 Air diffuser
– Compressed air is forced into this system through
the diffusers
– This air bubbles up through the water, mixing
water and air and introducing oxygen into the
water

Aerators
 Mechanical Aerator
– These aerators work by vigorously agitating the
water with mechanical mixers

Screening
 Screening usually involves a simple
screening or straining operation to remove
large solids and floating matter as leaves,
dead animals, fish etc.
– Bar screens - with openings of about 75mm
– Mesh screens - with opening of 5 - 20mm

Plain Sedimentation
 Sedimentation is the removal of particles (silt,
sand, clay, etc.) through gravity settling in
basins
 No chemicals is added to enhance the
sedimentation process
 Principle of plain sedimentation - Discrete
particles

sedimentation
vc: critical velocity, m/h
Q: flow rate, m3/h
Td: detention time, h
A: area of top of basin settling zone, m2
SOR: surface overflow rate, m3/m2.h

Sedimentation Tank
 The velocity of flow can be reduced by increasing the
length of travel and by detaining the particle for a
longer time in the sedimentation basin
 The size and the shape of the particles can be
altered by the addition of certain chemicals in water
(coagulants)
 Sedimentation Tanks are generally made of
reinforced concrete and may be rectangular or
circular in plan
 Long narrow rectangular tanks with horizontal flow
are generally preferred to the circular tanks with
radial or spiral flow

Inlet zone
 to distribute the water inside the tank
 to control the water's velocity as it enters the
basin
 A most suitable type of an inlet for a rectangular
settling tank is in the form of a channel extending
to full width of the tank with a submerged weir
type baffle wall

Out let zone
 Outlet arrangement consists of
– weir, notches or orifices
– effluent trough or launder
– outlet pipe

Design parameters of sedimentation tank
1. Detention period ….. 3 to 4 hours for plain settling
2 to 2.5 hours for coagulant settling
1 to 1.5 hours for vertical flow type
2. Overflow rate ……… 15 - 30 m3/m2/day for plain settling
30 - 40m3/m2/day for horizontal flow
40 - 50m3/m2/day for vertical flow
3. Velocity of flow…….. 0.5 to 1.0 cm/sec
4.Weir loading………... 300m3/m/day
5. L:W ………………….. 3:1 to 5:1
Breadth of tank…….. (10 to 12m) to 30 to 50m
6. Depth of tank………. 2.5 to 5m (with a preferred value of 3m)
7. Diameter of circular tank…. up to 60m
8. Solids removal efficiency….. 50%
9. Turbidity of water after sedimentation – 15 to 20 NTU.
10. Inlet and Outlet zones………. 0.75 to 1.0m
11. Free board…………………… 0.5m
12. Sludge Zone…………………. 0.5m

What is Coagulation?
 Coagulation is the destabilization of colloids by
addition of chemicals that neutralize the negative
charges
 The chemicals are known as coagulants, usually
higher valence cationic salts (Al3+, Fe3+ etc.)
 Coagulation is essentially a chemical process

Coagulation (Coagulation Aided with
Sedimentation)
 To remove very fine particles from the water
 Adding of this chemical process is called
coagulation and the chemical used in the
process is called coagulant
 Objective, to form a flocs

Typical coagulants
 Aluminum sulfate: Al2(SO4)3.14 H2O
 Iron salt- Ferric sulfate: Fe2(SO4)
 Iron salt- Ferric chloride: Fe2Cl3
 Polyaluminum chloride (PAC): Al2(OH)3Cl3

Colloid Destabilization
be destabilized by charge
 Colloids can
neutralization
 Positively charges ions (Na+, Mg2+, Al3+,
Fe3+ etc.) neutralize the colloidal negative
charges and thus destabilize them.
 With destabilization, colloids aggregate in
size and start to settle
99

Jar Tests
 The jar test – a laboratory procedure to
determine the optimum pH and the optimum
coagulant dose
 A jar test simulates the coagulation and
flocculation processes

Jar Tests
 Determination of optimum pH
 Fill the jars with raw water sample
(500 or 1000 mL) – usually 6 jars
 Adjust pH of the jars while mixing
using H2SO4 or NaOH/lime
(pH: 5.0; 5.5; 6.0; 6.5; 7.0; 7.5)
Add same dose of the selected
coagulant (alum or iron) to each jar
(Coagulant dose: 5 or 10 mg/L)
Jar Test

Determination of optimum pH
 Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid mix
helps to disperse the coagulant throughout each container
Reduce the stirring speed to 25 to 30 rpm
and continue mixing for 15 to 20 mins.
This slower mixing speed helps
promote floc formation by
enhancing particle collisions,
which lead to larger flocs
 Turn off the mixers and allow
flocs to settle for 30 to 45 mins
 Measure the final residual
turbidity in each jar
 Plot residual turbidity against pH

Jar Tests – optimum pH
Optimum pH: 6.3

Optimum coagulant dose
 Repeat all the previous steps
 This time adjust pH of all jars at
optimum (6.3 found from first test)
while mixing using H2SO4 or
NaOH/lime
Add different doses of the selected
coagulant (alum or iron) to each jar
(Coagulant dose: 5; 7; 10; 12; 15; 20 mg/L)
 Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid
mix helps to disperse the coagulant throughout each container
 Reduce the stirring speed to 25 to 30 rpm for 15 to 20 mins

Optimum coagulant dose
 Turn off the mixers and allow flocs to settle for 30 to 45 mins
 Then measure the final residual turbidity in each jar
 Plot residual turbidity
against coagulant dose
The coagulant dose with
the lowest residual
turbidity will be the
optimum coagulant dose
Coagulant Dose mg/L
Optimum coagulant dose: 12.5 mg/L

Filtration
 Removal of colloidal (usually destabilized)
and suspended material from water by
passage through layers of porous media.

Types of Granular Filters
 Based on filter media
– Slow sand filtration
– Rapid filtration
– High-rate filters
 Based on driving force
– Gravity filters
– Pressure filters
 Based on flow direction
– Down flow filters
– Up flow filters

Particle Removal Mechanisms in
Filters

Filter media size parameters
– Effective size (d10): the size of standard sieve
opening that will pass 10% by weight of the media
– Uniformity coefficient (UC): the ratio of the
standard sieve opening that will pass 60% by
weight of the media (d60) to its effective size.
10
60
d

d
UC

 Slow sand filter consists of concrete/brick work
rectangular basin containing carefully selected graded
sand supported on gravel and stones.
Slow Sand Filter

Mechanisms of impurities removal in
SSF
 Physical:Mechanical straining/sedimentation
 Chemical: Oxidation of organic matter by
aerobic bacteria
 Biological: Occurs through Schmutzdecke
or “Vital layer”. Schmutzdecke is a layer of
dirt, debris, and microorganisms build up on
the top of the sand

Slow Sand Filter Cleaning
 Periodic raking and cleaning of
the filter by removing the top
two inches of sand. After a
few cleanings, new sand must
be added to replace the
removed sand.
 After a cleaning the filter must
be operated for two weeks,
with the filtered water sent to
waste, to allow the
schmutzdecke layer to rebuild.
 Two slow sand filters should
be provided for continuous
operation.

Advantages and Disadvantages of SSF
 Advantages:
– Simple to construct and operate
– Cost of construction cheaper than rapid sand filter
– Do not usually require coagulation/flocculation before
filtration
– Bacterial count reduction is 99.9% to 99.99% and E.coli
reduction is 99% to 99.9%
 Disadvantages:
– Initial cost is low but maintenance cost is much more than
rapid sand filter
– These filters need a lot of space

Design criteria for slow sand filters
Parameter Recommended level
Design life 10-15 year
Period of operation 24 h/day
Filtration rate 0.1 – 0.2 m/h
Filter bed area 5-200 m2/filter
Height of filter bed
Initial 0.8-0.9 m
Minimum 0.5-0.6 m
Effective size 0.15-0.3 mm
Uniformity coefficient < 3
Height of under drains including 0.3-0.5 m
gravel layer
Height of supernatant water 1 m

Disinfection
 Treatment used for destruction or removal of
pathogens
 Widely used disinfectants
– Oxidizing agents (halogens, halogen compounds, ozone)
– Physical agents (Ultraviolet radiation)
 Factors that affect efficiency of disinfection
– Type and concentration of microorganisms
– Type and concentration of disinfectant
– Contact time provided
– Character and temperature of the water

Characteristics of an Ideal Disinfectant
 Kill or disable pathogens
 Nontoxic to consumers
 Cheap and easy to use
 Fast acting and long lasting
 Improve water aesthetics

Disinfectants in common use
 Chlorine (Cl2)
 Chloramines (NH2Cl, NHCl2)
 Chlorine dioxide (ClO2)
 Ozone (O3)
 Ultraviolet (UV) radiation.

Chlorination
 Widely used disinfectant
 Advantages: readily available as gas, liquid
or solid; cheap; easy to apply; toxic to most
microorganisms; provides protection in the
distribution system
 Disadvantages: Fatal at high
concentrations; Toxic; Irritant; Corrosive;
Formation of harmful disinfection by-products
(DBPs) like Trihalomethanes (THMs)

Chloramines
 Advantages
– Less corrosive
– Less toxicity and chemical hazards
– Relatively tolerable to inorganic and organic loads
– No known formation of DBP
– Relatively long-lasting residuals
 Disadvantages
– Not so effective against viruses, protozoan cysts,
and bacterial spores

Hypochlorites
 Less pure and dangerous than chlorine gas
 Strength decreases with time while in storage
 Safer to handle but expensive
 Types:
– Sodium hypochlorite (NaOCl) solution
– Calcium hypochlorite (CaO(Cl)2)
 Reactions:
Ca(OCl)2 + 2 H2O  2 HOCl + Ca(OH)2
NaOCl + H2O  HOCl + NaOH

UV Disinfection
 Physical method of inactivating pathogens.
 Mechanism of UV Disinfection:
– Radiation with an wavelength of around 260 nm
penetrates the cell wall and cell membrane of
microorganisms and is absorbed by cell material
such as DNA and RNA and promotes changes
that prevents replication to occur

Miscellaneous Water Treatment Processes
 Removal of dissolved gases
 Removal of Iron and manganese
 Removal of silica
 Fluoridation
 Removal of oil
 Softening (refer the removal of hardness in
chapter three)

WATER DISTRIBUTION SYSTEM
 After treatment, water is to be stored
temporarily and supplied to the consumers
through the network of pipelines called
distribution system.
 The distribution system also includes
– pumps,
– reservoirs,
– pipe fittings,
– instruments for measurement of pressures, flow leak
detectors etc

Requirement of Distribution System
 The system should convey the treated water up to
consumers with the same degree of purity
 The system should be economical and easy to maintain
and operate
 It should safe against any future pollution. As per as
possible should not be laid below sewer lines.
 Water should be supplied without interruption even
when repairs are undertaken
 The system should be so designed that the supply
should meet maximum hourly demand

System of Distribution
 Depending upon the methods of distribution, the
distribution system is classified as the follows
– Gravity system
– Pumping system
– Dual system or combined gravity and pumping
system

Gravity System
 When some ground sufficiently high above the
city area is available

Pumping System
 Constant pressure
can be maintained
in the system by
direct pumping into
mains
 Supply can be
affected during
power failure and
breakdown of
pumps

Combined Pumping and Gravity System

Methods of Supply of Water
 Continuous System
– This is the best system and water is supplied for all
24 hours. This system is possible when there is
adequate quantity of water for supply.
 Intermittent System
– If plenty of water is not available, the supply of water
is divided into zones and each zone is supplied with
water for fixed hours in a day or on alternate days

 The system has following disadvantages:
– Consumers have to store water for non-supply hours.
– Bigger sized pipes are to be laid, because full day’s
supply is to be provided within few hours of supply.
– Pipelines are likely to rust faster due to alternate
wetting and drying. This increases the maintenance
cost.
– There is also pollution of water by ingress of polluted
water through leaks during non-flow periods.

Layouts of Distribution System
 Generally in practice there are four different
systems of distribution which are used. They
are:
– Dead End or Tree system
– Grid Iron system
– Circular or Ring system
– Radial system

Dead End or Tree System
 This system is suitable for irregular developed
towns or cities.

 Advantages:
– Discharge and pressure at any point in the
distribution system is calculated easily
– The valves required in this system of layout are
comparatively less in number.
– The diameter of pipes used are smaller and hence
the system is cheap and economical
– The laying of water pipes is used are simple.

 Disadvantages:
– There is stagnant water at dead ends of pipes
causing contamination.
– During repairs of pipes or valves at any point the
entire downstream end are deprived of supply
– The water available for firefighting will be limited in
quantity

Grid Iron System
 From the mains water enters the branches at all
junctions in either direction into sub-mains of
equal diameters.

Grid Iron System
 Advantages
– As water is supplied from both the sides at any point,
very small distribution area will be affected during
repair.
– Every point receives supply from two directions and
with higher pressure
– In case of fire, more quantity of water can be diverted
towards the affected area, by closing the valves of
nearby localities.
– There is free circulation of water and hence it is not
liable for pollution due to stagnation.

Grid Iron System
 Disadvantages:
– More length of pipes and number of valves are
needed and hence there is increased cost of
construction
– Calculation of sizes of pipes and working out
pressures at various points in the distribution system
is laborious, complicated and difficult.

Circular or Ring System
 Supply to the inner pipes is from the mains
around the boundary. It has the same
advantages as the grid-Iron system. Smaller
diameter pipes are needed. The advantages
and disadvantages are same as that of grid-Iron
system.

Radial System
 Water is pumped to the distribution reservoirs
and from the reservoirs it flows by gravity to the
tree system of pipes.
 The pressure calculations are easy in this
system. Layout of roads needs to be radial to
eliminate loss of head in bends. This is most
economical system also if combined pumping
and gravity flow is adopted.

Pressure in the Distribution System
 When the water enters in the distribution main,
the water head continuously is lost due to
friction in pipes, at the entrance of reducers, due
to valves, bends, meters etc till it reaches the
consumers tap
 The effective head available at the service
connection to a building is very important,
because the height up to which the water can
rise in the building will depend on this available
head only

The pressure in the distribution system
depends upon the factors as listed below:
– The height of highest building where water should
reach with adequate pressure, without boosting
– Pressure required for fire hydrant
– The distance of the locality from the distribution
reservoir.

The following pressures are considered
satisfactory in the case of multi-storied
buildings.
 One storey only 7m head
 Two storey building 12m head
 Three storey building 17m head
 3 to 6 storey heights 2.1 to 4.2kg/cm2 (21
to 42m)
 6 to 10 storey heights 4.2 to 5.2kg/cm2
 Above 10 storey 5.27 to 7kg/cm2

Service/Distribution Reservoirs
 A service reservoir has four main functions:
– To balance the fluctuating demand from the
distribution system, permitting the source to give
steady or differently phased output.
– Provide a supply during a failure or shutdown of
treatment plant, pumps or trunk main leading to the
reservoir.
– To give a suitable pressure for the distribution system
and reduce pressure fluctuations therein.
– To provide a reserve of water to meet fire and other
emergency demands.

Types of Service Reservoirs
 Generally, there are two types of service reservoirs:
– Surface reservoir (Ground Reservoir or Non-elevated)
– Elevated reservoir ( Over head Tank)

Accessories of Service Reservoirs
 Inlet Pipe : For the entry of water
 Ladder : To reach the top of the reservoir and
then to the bottom of the reservoir, for inspection
and cleaning
 Lightening Conductor : In case of elevated
reservoirs for the passage of lightening
 Manholes : For providing entry to the inside of
reservoir for inspection and cleaning
 Outlet pipe: For the exit of water

Cont’d
 Outflow Pipe : For the exit of water above full
supply level
 Vent pipes : For free circulation of air
 Washout pipe : For removing water after
cleaning of the reservoir
 Water level indicator: To know the level of
water inside the tank from outside.

Accessories of service reservoir
LIGHTENING CONDUCTOR
OUTLET PIPE
INFLOW PIPE
WATER LEVEL INDICATOR
WASH OUT PIPE
DITCH
OVER FLOW PIPE
MANHOLE
LADDER

Design Capacity of Service Reservoirs
 Analytically by finding out maximum cumulative
surplus during the stage when pumping rate is
higher than water consumption rate and adding
to this maximum cumulative deficit which occurs
during the period when the pumping rate is
lower than the demand rate of water

 By drawing mass curves (graphical method)
– A mass diagram is the plot of accumulated inflow (i.e.
supply) or outflow (i.e. demand) versus time. The
mass curve of supply (i.e. supply line) is, therefore,
first drawn and is superimposed by the demand
curve.

Example 1:
 A small town with a design population of 1600 is
to be supplied water at 150liters per capita per
day. The demand of water during different
periods is given in the following table:
Time
(hr)
0 - 3 3 - 6 6 - 9 9 - 12 12 - 15 15 - 18 18 - 21 21- 24
Demand
(1000lit
ers)
20 25 30 50 35 30 25 25
• Determine the capacity of a balancing reservoir if pumping is done 24 hours
at constant rate.

Solution:
 Per capita water consumption = 150l/c/d
 Total water demand = demand * population =
150*1600 = 240,000liters
 Rate of pumping = 240,000/24 = 10,000lit/hr =
30,000lit/3hr

Analytical Method
Time Pumping Demand Cum. Supply Cum. Demand Surplus Deficit
0 - 3 30,000 20,000 30,000 20,000 10,000
3 - 6 30,000 25,000 60,000 45,000 15,000
6 - 9 30,000 30,000 90,000 75,000 15,000
9 - 12 30,000 50,000 120,000 125,000 5,000
12 - 15 30,000 35,000 150,000 160,000 10,000
15 - 18 30,000 30,000 180,000 190,000 10,000
18 - 21 30,000 25,000 210,000 215,000 5,000
21 - 24 30,000 25,000 240,000 240,000 0 0

Cont’d
 Maximum cumulative surplus = 15,000 liters
 Maximum cumulative deficit = 10,000 liters
 Balancing storage = 15000 + 10000 = 25,000lit
= 25m3
If the reservoir is circular with depth, h = 3.0 m,
m
d 4
.
3
3
4
*
25




Example 2
Consider example 1, if the pumping is done for:
– Eight hours from 8 hrs to 16 hrs
– Eight hrs from 4 hrs to 8 hrs and again 16 hours to 20
hrs.
Calculate the capacity of the balancing reserve.
Solution:
 Total water demand = 240,000lit/hr
 Rate of pumping = 240,000/8 = 30,000l/h =
90,000lit/3hrs

Eight hours from 8 hrs to 16 hrs
A) Analytical Method
Time Pumping Demand
Cum.
Supply
Cum.
Demand
Surplus Deficit
0 - 3 0 20000 0 20000 20000
3 - 6 0 25000 0 45000 45000
6 - 8 0 20000 0 65000 65000
8 - 9 30000 10000 30000 75000 45000
9 - 12 90000 50000 120000 125000 5000
12 - 15 90000 35000 210000 160000 50000
15 - 16 30000 10000 240000 170000 70000
16 - 18 0 20000 240000 190000 50000
18 - 21 0 25000 240000 215000 25000
21 - 24 0 25000 240000 240000 0 0

Maximum cumulative surplus = 70,000
Maximum cumulative deficit = 65,000
Balancing storage, S = 135,000lit =
135m3

Depth and Shape of Service Reservoirs
 Depth
Size (m3) Depth of water
(m)
Up to 3500 2.5 to 3.5
3500 to 15,000 3.5 to 5.0
Over 15,000 5.0 to 7.0

Factors influencing depth for a given
storage are:
 Depth at which suitable foundation conditions are
encountered
 Depth at which the out let main must be laid
 Slope of ground, nature and type of back fill
 The need to make the quantity of excavated material
approximately equal to the amount required for backing,
so as to reduce unnecessary carting of surplus material
to tip.
 The shape and size of land available

Shape
 Circular reservoir is geometrically the most economical
shape, giving the least amount of walling for a given
volume and depth
 A rectangular reservoir with a length to width ratio 1.2 to
1.5

Pipes Used in the Water Distribution
System
Pipe Materials
 Pipe materials used in transmission and
distribution systems must have the following
characteristics
– Adequate tensile strength and bending strength to withstand
external loads.
– High bursting strength to withstand internal water pressure
– Ability to resist impact loads to water flow suitable for handling
and joining facilities
– Resistance to both internal and external corrosion

The types of pipes used for distributing
water include:
 Cast iron pipe
 Steel pipe
 Concrete pipe
 Plastic pipe
 Asbestos cement pipe
 Copper pipe
 Lead pipe

A pipe material is selected based on
various conditions:
 Cost
 Type of water to be conveyed
 Carrying capacity of the pipe
 Maintenance cost
 Durability, etc.

Cast iron pipes
 Advantages:
– The cost is moderate
– The pipes are easily joined
– The pipes aren’t subjected to corrosion
– The pipes are strong and durable
– Service connections can be made easily
– Disadvantage:
– The breakage of this pipe is large
– Carrying capacity decreases with increase in life
– The pipes become heavy and uneconomical when their sizes
increase (especially beyond 1200mm)
Advantages:

Galvanized Iron Pipes
 Advantages:
– The pipes are cheap
– Light in weight and easy to handle and transport
– Easy to join
 Disadvantage:
– These pipes are liable to incrustation (due to
deposition of some materials inside part of pipe)
– Can be easily affected by acidic or alkaline water
– Short useful life

Plastic Pipes
 Advantages:
– The pipes are cheap
– The pipes are flexible and possess low hydraulic
resistance (less friction)
– They are free from corrosion
– The pipes are light in weight and it is easy to bend,
join and install them
– The pipes up to certain sizes are available in coils
and therefore it becomes easy to transport

 Disadvantage:
– The coefficient of expansion for plastics is high, the
pipes are less resistant to heat
– Some types of plastics may impart taste to the water

Appurtenances in the Distribution System
 The various devices fixed along the water
distribution system are known as
appurtenances.
 The following are the some of the fixtures used
in the distribution system.
– Valves
– Fire hydrants and
– Water meter

Types of Valves
 The following are the various types of valves
named to suit their function
– Sluice valves
– Check valves or reflex valves
– Air valves
– Drain valves or Blow off valves
– Scour valve

Valves
Sluice valves
– These are also known as gate-valves or stop valves.
– These valves control the flow of water through pipes.
Check Valve or Reflux Valve
– These valves are also known as non-return valves. A
reflux valve is an automatic device which allows
water to go in one direction only

Air Valves
 These are automatic valves and are of two types
namely
– Air inlet valves
– Air relief valves
 Air Inlet Valves
– These valves open automatically and allow air to
enter into the pipeline so that the development of
negative pressure can be avoided in the pipelines.

– The vacuum pressure created in the down
streamside in pipelines due to sudden closure of
sluice valves
– This situation can be avoided by using the air inlet
valves.
 Air Relief Valves
– Sometimes air is accumulated at the summit of
pipelines and blocks the flow of water due to air lock.
In such cases the accumulated air has to be removed
from the pipe lines.

 Drain Valves or Blow off Valves
– These are also called wash out valves they are
provided at all dead ends and depression of pipelines
to drain out the waste water.

Water Meter
 These are the devices which are installed on the
pipes to measure the quantity of water flowing at
a particular point along the pipe.
 The readings obtained from the meters help in
working out the quantity of water supplied and
thus the consumers can be charged accordingly.

Fire Hydrants
 A hydrant is an outlet provided in water pipe for
tapping water mainly in case of fire.
 They are located at 100 to 150 m a part along
the roads and also at junction roads.

Determination of Pipe Sizes
 Permissible velocities for best results for
different pipe sized pipes are within the range of
0.3 to 2m/s.
 Once the velocity of flow is established loss of
head due to friction, bends and other reasons
can be computed
 The head required to develop a particular
velocity in a particular sized pipe is then
calculated.

 The size of the pipe used in the water
distribution system or the velocity of flow
through the pipe can be determined by one of
the following formulas:
 Darcy –Weisbach formula:
 Hazen-Williams formula:
 Manning’s Formula:
gD
fLV
hf
2
2

L
h
S
S
CD
Q f

 ,
278
.
0 54
.
0
63
.
2
n
S
AR
Q
2
/
1
3
/
2


 The most common pipe flow formula used in
design and evaluation of a water distribution
system is the Hazen-Williams’ formula.
L
h
S
S
CD
Q f

 ,
278
.
0 54
.
0
63
.
2

Water supply pipes sizes commercially available are given
in the following table:
Metric
sizes (mm)
10 20 25 30 40 50 60 80 100 150 200 250 300
English
(In)
½ 3/4 1 11/4 11/4 2 21/2 3 4 6 8 10 12
Metric
sizes
(mm)
350 375 400 450 500 525 600 675 750 900 950 1050
English
(In)
14 15 16 18 20 21 24 27 30 36 38 42

Example 1:
 Given
– Total population of a town = 80,000
– Average daily consumption of water =
150liters/capita/day
– If the flow velocity of an outlet pipe from intake = 1.5
m/s, determine the diameter of the outlet pipe.

Exp. Cont’d..
 Solution
 Total flow, Q = Demand* Population =
150*80,000 = 12x106 lit/day
 Required pipe area,
 But the pipe size available on the market is
300mm & 350mm, then take D = 350mm
mm
V
Q
D
V
Q
D
V
Q
A 343
*
5
.
1
4
*
1389
.
0
4
4
4
2










Example 2:
 A town has a population of 100,000 persons. It
is to be supplied with water from a reservoir
situated at a distance of 6.44km. It is stipulated
that one-half of the daily supply of 140lit/capita
should be delivered in 6 hours. If the loss of
head is estimated to be 15m, calculate the size
of pipe. Assume f = 0.04.

Exp. Cont’d..
Solution
 Total daily supply =
 Since half of this quantity is required in 6 hours
 Maximum flow =
 According to the Darcy-Weisbach formula:
Where, hf = 15m, f = 0.04, L = 6440m
3
3
000
,
14
10
000
,
100
*
140
m

s
m /
324
.
0
)
60
*
60
*
6
*
2
(
000
,
14 3

5
2
1
.
12 d
fLQ
hf 

 But available pipe sizes 675mm & 750mm, take
750mm diameter pipe
mm
m
d
d
683
683
.
0
10
.
12
*
15
)
324
.
0
(
*
6440
*
04
.
0
*
1
.
12
)
0324
(
*
6440
*
04
.
0
15
2
5
2






Energy Losses in Pipes
 The major energy loss (head loss) in pipes can
be found by one of the three formulas:
 Darcy-Weisbach
Where, hf = head loss (m)
f = friction factor (which is related to the relative
roughness of the pipe material & the fluid flow
characteristics)
L = length of pipe (m)
gD
fLV
hf
2
2


 Hazen-Williams formula
Where, C = Coefficient that depends on the material and
age of the pipe
S = Hydraulic gradient (m/m)
L
h
S
S
CD
Q
f

 ,
278
.
0 54
.
0
63
.
2

 Table - Values of C for the Hazen-Williams
formula
Pipe Material C
Asbestos Cement 140
Cast Iron
 Cement lined
 New, unlined
 5years-old, unlined
 20 years old, unlined
130 – 150
130
120
100
Concrete 130
Copper 130 - 140
Plastic 140 - 150
New welded Steel 120
New riveted Steel 100

 Nomographs solve the equation for C = 100.
Given any two of the parameters (Q, D, hf or V)
the remaining can be determined from the
intersections along a straight line drawn across
the nomograph.
 Manning’s Formula
, R = D/4, S = hf/L
n
S
AR
Q
2
/
1
3
/
2


 Where, n = Coefficient of roughness depending
on pipe material, usually
n = 0.013 GI pipes
n = 0.009  Plastic pipes
n = 0.015  Clay concrete pipes

Procedure of Analyzing Pipe Size and
Pressure
 Assume any internally consistent distribution of flow. The sum of the
flows entering any junction must equal the sum of the flows leaving
 Compute the head losses in each pipe by means of an equation or
diagram. Conventionally, clockwise flows are positive and produce
positive head losses.
 With due attention to sign, compute the total head loss around each
circuit: hL = KQn.
 Compute, without regard to sign, for the same circuit, the sum of:
KnQn-1.
 Apply the corrections obtained from equation to the flow in each
line. Lines common to two loops receive both corrections with due
attention to sign.

water supply and Treatment (2).pptx

water supply and Treatment (2).pptx

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to water supply and Treatment (2).pptx

Similar to water supply and Treatment (2).pptx (20)

Recently uploaded

Recently uploaded (20)

water supply and Treatment (2).pptx