Water supply Engineering Notes by Sudip Khadka.pdf

Water Supply Engineering
Prepared By:- Sudip Khadka
Engineering Students
Purbanchal University
Chapter 2: SOURCES OFWATER

1. Classificationof sourcesof water
2. Surfacesources
1. Rivers
2. Streams
3. Lakes
4. Ponds
5. Impounded reservoir
6. Numerical on capacity determination of impounded reservoir
3. Groundsources
1. Confined and unconfined aquifers
2. Springs
3. Wells
4. infiltrationgalleriesand wells
4. Selectionof water sources
Chapter-2SourcesofWater
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Chapter 2: SOURCES OFWATER

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Classification of sources ofwater
1. SurfaceSources
2. Groundsources
Sources of
water
Surface sources
1. Ponds/Lakes
2. Rivers/Streams
3. Oceans/Seas
4. Reservoirs
Sub-surface
(Ground) Sources
1. Infiltrationwells
2. Infiltrationgalleries
3. Wells/ Boreholes
4. Aquifers(confined/unconfined)

SurfaceSources
• “ The water which is available on the surface of earth is
known as surface water”
• Surface water is prone to contaminationfrom human
and animals
• Surface water needs purificationbefore use for drinking
and cooking purpose
• Examples:
• River/Stream
• Lake/Ponds
• Sea/Ocean
• Impounded reservoirs

Ponds
• A depressed land filled with water
• Can be natural or man-made,
stagnant water
• Purpose: fish farming, irrigation,
cattle bathing, swimming etc.
• Features:
• Quantity: limited
• Quality: large amount of impurities,
bacteria
• Treatment: sedimentation,
screening, filtration and many more
• Economic: uneconomical can’t be
used for drinking

Lakes
• Naturalbasin withimpervious
bed
• Collects water from rain,
spring, streamsand rivers
• Features:
• Quantity: depends upon capacity,
catchment area, rainfall, porosity
of land
• Quality: depends upon locality
• Treatment: primary or secondary
based on quality
• Economic: comparatively
expensive

Streams
• Startswithrainfalland destination is
a river
• Theymostlyoriginateduring rainy
season and will havegooddrainage
• Theywill haveless or even get dry on
other season
• Features:
• Quantity: good dischargein rainy season
• Quality: water is of good quality
• Treatment: minimum, screening and
sedimentationwill be sufficient
• Economic: rainy season- very
economical

River
• Startsfrom Run-off(origin may be: streams,
springs, glacier) and ends to sea/ocean/
reservoir
• Types:
• Perennial River: water is available
throughout the year. Used for water supply
• Non-perennial river: water is available on
certain period of the year and remains dry
on remaining interval.
• Features:
• Quantity/Feasibility: Reliable (based on
type)
• Quality: comparatively safe
• Origin: pure/safe
• With lengthand location may add impurities
• Economic: relatively economical
• Treatment: primary or secondary (self-
cleansing velocity)

ImpoundedReservoirs
• These are artificially lakes
constructed to store large
quantitiesof surface water
• They are usually of earthwork or
masonry structures
• These are created by constructing
dams, weirs, bund etc. across the
valleys cut by streams
• The area draininginto the
reservoir is called “catchment
area”
• They are constructedusually
when the river has insufficient
dischargeto meet demand
mainly during summer season

• Features:
• Quantity: sufficient to serve the demand
• Quality: depends upon quality of river water, fairly good quality,
clear, palatable and considered to be free from pathogenic
organisms
• Treatment: needed
• Economy: high construction cost + running cost
• Site selection criteria for reservoirs:
• Narrow river channel
• Higher elevation than treatment plant and distribution area
• Availability of sufficient water
• Accessible location with favorable topography
• Less polluted watershed and river bed

Capacity determinationof ImpoundedReservoir
1. Capacity depends on inflow(discharge) and demand
2. River Discharge > Demand (throughout the year) = No need of
reservoir
3. River discharge < Demand; during dry season
River Discharge is maximum in other period =
impounded reservoir
• Methods:
1. Graphical method or Mass Curve Method
2. Hydrographmethod
3. AnalyticalMethod

AnalyticalMethod
•Capacity of the reservoir is determined from the net
inflow and demand.
•Storage is required when the demand exceeds the net
inflow.
•The total storage required is equal to the sum of the
storage required during the various periods.
• Assumption: reservoir is full at the beginning of dry
season

Procedure:
1. Collect the streamflow dataat the reservoirsite during the
criticaldry period.Generally, the monthlyinflow rates are
required. However,for verylarge reservoirs,the annual
inflow rates maybe used.
2. Ascertainthe dischargeto be releaseddownstreamto satisfy
water rights or to honor the agreementbetweenthe states
or the cities.
3. Determine the direct precipitationvolume falling on the
reservoirduring the month.
4. Estimatethe evaporationlosses which wouldoccur from the
reservoir. The pan evaporationdata are normallyused for
the estimationof evaporationlosses during the month.
5. Ascertainthe demand during variousmonths.

6.Determine the adjustedinflow (I)during differentmonths
as follows:
Adjustedinflow(I)= Streaminflow + Precipitation-
Evaporation– DownstreamDischarge
7. Compute the storage capacityfor each months. Storage
required= Adjustedinflow(I)– Demand(O) If the value
is negative,deficiency(D)occurs.
If the value is positive,surplus(S)occurs.
8.Determine the totalstorage capacityof the reservoirby
adding the storagesrequiredfound in Step 7.
“If the totaldeficiencyis greaterthan totalsurplus,the
projectis not feasibledue to low inflow.” In other words,the
totalstorage capacityshould be positivefor the projectto be
feasible.

Q. 1
The yield of water from a catchment area is given
below. Determine analytically the minimum storage
capacity of impounded reservoir to maintain a
constant draft of 4.4 million 𝑚3of water per month.
Neglect all loses and wastages.
M
o
n
t
h Jan F
e
b M
a
r April M
a
y J
u
n
e July A
u
g Sept O
c
t N
o
v D
e
c
Inflowmillionm
3 1.5 2.0 2.5 5.0 6.0 8.2 9.0 7.5 5.0 3.5 3.1 2.0

Solution;
Month
Inflow
(million m^3)
"I"
Outflow
(million m^3)
"O"
Deficit
(million m^3)
"D"
Surplus
(million m^3)
"S"
Jan 1.5 4.4
Feb 2 4.4
March 2.5 4.4
April 5 4.4
May 6 4.4
June 8.2 4.4
July 9 4.4
August 7.5 4.4
Sept 5 4.4
Oct 3.5 4.4 Calculate( I-O), -ve is D and +ve is S
Nov 3.1 4.4
Dec 2 4.4
Total 55.3 52.8

Month
Inflow
"I"
Outflow
"O"
Deficit
"D"
Surplus
"S"
Jan 1.5 4.4 2.9
Feb 2 4.4 2.4
March 2.5 4.4 1.9
April 5 4.4 0.6
May 6 4.4 1.6
June 8.2 4.4 3.8
July 9 4.4 4.6
August 7.5 4.4 3.1
Sept 5 4.4 0.6
Oct 3.5 4.4 0.9
Nov 3.1 4.4 1.3
Dec 2 4.4 2.4
Total 55.3 52.8 11.8 14.3
Here, the total deficit is
less than total surplus.
So the project is feasible.
Thus,
required minimum
reservoir capacity= total
deficit
= 11.8 million 𝑚3

Q. 2
A city has a average water demand of 6202 million
liters per month. Calculate the capacity of
impounded reservoir.The flow in the river is shown
below:
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Inflow
(m^3/s) 2.97 1.99 1 0 0.51 1 2 3 4 5 4 2
1𝑚3/𝑠= 1000 liter/s=1000*60*60*24 liters/day=86.4*106 liters/day

Solution:
Month Days
Inflow
(m^3/
s)
Volume (I)
(million
litres)
Demand(O
)(million
litres)
Deficit (D)
(million
litres)
Surplus (S)
(million
litres)
Jan 31 2.97
=days*infl
ow*86.4 6202
I-O (-ve
values)
I-O (+ve
values )
Feb 28 1.99 6202
Mar 31 1.00 6202
Apr 30 0.00 6202
May 31 0.51 6202
Jun 30 1.00 6202
Jul 31 2.00 6202
Aug 31 3.00 6202
Sep 30 4.00 6202
Oct 31 5.00 6202
Nov 30 4.00 6202
Dec 31 2.80 6202
Total:
Sum of
defecit
Sum of
surplus

Solution:
Month Days
Inflow
(m^3/s)
Volume (I)
(million
litres)
Demand(O)
(million
litres)
Deficit (D)
(million
litres)
Surplus (S)
(million
litres)
Jan 31 2.97 7954.848 6202 1752.848
Feb 28 1.99 4814.208 6202 1387.792
Mar 31 1.00 2678.4 6202 3523.600
Apr 30 0.00 0 6202 6202.000
May 31 0.51 1365.984 6202 4836.016
Jun 30 1.00 2592 6202 3610.000
Jul 31 2.00 5356.8 6202 845.200
Aug 31 3.00 8035.2 6202 1833.200
Sep 30 4.00 10368 6202 4166.000
Oct 31 5.00 13392 6202 7190.000
Nov 30 4.00 10368 6202 4166.000
Dec 31 2.80 7499.52 6202 1297.520
Total: 20404.61 20405.57

Total deficit = 20404.61 million litres
Total surplus = 20405.57 million litres
Is total deficit < total surplus?
Yes, The project is feasible.
The required impounded reservoir capacity = total deficit
= 20404.61 million litres

Graphicalmethod; Mass inflow curve method
1. Prepare a mass inflow curve from the flow
hydrograph of the site for a number of consecutive
years including the most criticalyears (or the driest
years) when the discharge is low.
2. Prepare the mass demand curve corresponding to
the given rate of demand. If the rate of demand is
constant, the mass demand curve is a straight line.
The scale of the mass demand curve should be the
same as that of the mass inflow curve.

3.Draw the lines AB, FG, etc. such that (i) They are
parallel to the mass demand curve, and (ii) They are
tangential to the crests A, F,etc. of the mass curve.
4.Determine the vertical intercepts CD, HJ, etc.
between the tangential lines and the mass inflow
curve. These intercepts indicate the volumes by
which the inflow volumes fall short of demand.
Assuming that the reservoir is full at point A, the
inflow volume during the period AE is equal to
ordinate DE and the demand is equal to ordinate CE.
Thus the storagerequired is equal to the volume
indicated by the intercept CD.
5.Determine the largest of the vertical intercepts
found in Step (4). The largest vertical intercept
represents the storage capacity required.

The following points should be noted.
(i)The capacity obtained in the net storage capacity which
must be available to meet the demand. The gross capacity
of the reservoir will be more than the net storage capacity.
It is obtained by adding the evaporation and seepage losses
to the net storage capacity.
(ii)The tangential lines AB, FG; etc. when extended forward
must intersect the curve. This is necessary for the reservoir
to become full again, If these lines do not intersect the mass
curve, the reservoir will not be filled again. However,very
large reservoirs sometimes do not get refilledevery year. In
that case, they may become full after 2-3 years.
(iii)The vertical distance such as FL between the successive
tangents represents the volume of water spilled over the
spillway of the dam.

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Ground Sources ofWater
The water that is available/ found below the surface of
earth is known as ground water, and the source
containing that water is called ground source of water.
Quality of ground water is comparatively better as it
undergoes through various stratavia infiltrationand
percolation.

Types of ground sources ofwater
1. Springs
2. Infiltration galleries
3. Infiltration wells
4. Wells and borewells
5. Aquifers

Springs
• Types:
1. GravitySpring
i. Depression spring
ii. Surface or contact
spring
iii. Artesian spring
2. Non-gravitySpring

GravitySpring
Gravity Spring are formed when underground
water table is exposed on slopes of hills.
Types:
• Depression spring
• Surface spring
• Artesian spring

i. DepressionSpring
• Formed due to overflow of
water table where the ground
surface intersects the GWT
• When the ground water table
rise high then water overflows
out through the head of
natural valley
• Shallow and dependenton
precipitation.
• Quantity(Flow) varies with the
rise and fall of GWT

ii. Surface or ContactSpring
• Created when a permeable
water bearing formationis
overlayingover a less
permeable or impermeable
formation intersects the
ground surface.
• The quality of water
availablefrom such spring
is bit uncertain.

iii. Artesian spring
• These are formedunder
certain geological
condition.
• When the water stored in
two impervious strata
under pressure, overflows
to the ground surface, an
artesian spring is
observed.
• This type of spring has
capacity to produce
uniform quantity of water.

Non-gravity Spring
Non-gravity Spring are volcanic springs and fissure
springs which are formed either due to association of
volcanic rocks or due to fractures extending to a
greater depths in earth’s crust.
They are also known as hot springs and contain high
minerals and Sulphur.

Infiltration galleries
•Infiltrationgalleriesare horizontal
and nearlyhorizontaltunnel
constructedat shallowdepth (3 to
5m) along the bank of river
through the water bearing strata.
• Tocollectthe river water seeping
through their bottom.
• These wellsare constructedof
brick masonrywith open joints.
• Theyare generallycoveredat the
top and kept open at the bottom

Infiltration wells
• Vertical collection wells constructed
along the river/stream banks - water
infiltrates from both bottom and sides
• Suitable in areas with layer of sand and
porous material at least 2m in river bed
• A hand pump, windmill or power pump is
used to pump out water from the well
• Not affected by floods, silt/sand/gravel
loads, and extremely low waters in
rivers/streams
• Provides better quality water throughout
the year (filtration)
• The well can have radial porous pipes
(jack wells) Infiltration wells

Wells
It is a vertical structure dug in
ground for purpose of bringing
ground water to the earth’s
surface
Types of wells :
1. Open wells (Dug wells)
2. Tube wells

OpenWell
• These are the wells whichhave
comparativelylarge diameters
and lower discharges
• Usually they have discharge of
20 m³/hr but if constructed by
efficientplanning it gives
discharge of 200-300 m³/hr
• They are constructed of
diameter of about 1-10 m and
have depth of about 2-20m
• They are constructed by digging
therefore they are also known as
dug wells

Type of openwell
1. Shallow open well : These
are the wells resting on the
water bearing strataand
gets their supplies from the
surrounding materials
2. Deep open well : These are
the wells resting on the
impervious layerbeneath
which lies water bearing
pervious layer and gets their
supply from this layer

TUBEWELLS
A tube well is a long pipe
sunk in ground intercepting
one or more water bearing
strata.
As compared to open well
there diameter is less about
80-600 mm.
Depth of tube well range
from 330m (shallow tube
well) to 600m (deep tube
well)

Types of tubewell
• Strainertype Tube Well
• CavityTube Well
• Slottedtype Tube Well
• Perforated type TubeWell

Strainer type tubewell
• These is most commonly used tube
such that in general a tube well
means strainer tube well.
• In this type of well a strainer which
a wire mesh with small openings is
wrapped around the main pipe
which also has large openings such
that area of opening in strainer and
main pipe remains same.
• Annual space is left between two
strainer so that the open area of
pipe perforations is not reduced.
The type of flow is radial.

Cavity tube well:
• A cavity type tube well
consists of a pipe sunk in
ground up to the hardclay
layer .
• It draws water fromthe
bottom of well .
• In initial stages fine sand is
also pumped with water
and in such manner a
cavity is formed at the
bottom so the water enters
from the aquifer into the
well through this cavity

Slotted type tubewell
• When suitable strongroofing
layer is not available for the
construction of a cavity well.
• This well consists of a slotted
wrought iron tube penetrate
a highly pervious confine
aquifer.
• By developing the wellwith
the help of compressed air,
the sand surrounding the
gravel is freed from finer
particles.

Aquifers
• A natural storage reservoir which
holds water below the ground and
from where water can be
withdrawn.
• A saturated ,permeable , geologic
unit that can transmit a significant
amount of groundwater under an
ordinarily gradient.
• Aquifer is body of saturated rock or
sediment through which water can
move easily.
• Examples: sand stone,
conglomerate, well jointed
limestone, highly fractured rock etc.

Types of Aquifer
1. Confined aquifer:
This type of aquiferis confinedunder
pressure by overlayingimpermeable
strata.
Also known as artesian/pressure
aquifer.
Rechargesvery slowly
It occur where groundwateris confined
under pressuregreaterthan
atmosphericby overlyingrelatively
impermeable strata.

Types of Aquifer
2. Unconfined aquifer:
An aquifer that is bounded from above
by a phreatic surface is called a phreatic
or unconfined aquifer, or a water table
aquifer
Has a water table, and is only partly
filled with water.
Rapidly recharged by precipitation
infiltrating down to the saturated zone

ArtesianWells
• These type of wellshavewell
head below water table so
water flowsunder pressure
• Do not need externalpumping
to take water
• These wellsare createdwhen
a pervious stratum is enclosed
betweentwo impervious
strata with an opening so high
above the ground
• This are usuallyfoundinvalley
• Quality:similarto dug well

• Aquifer
• Aquifuge
• Aquitard
• Aquiclude
Technical terms
Name Holds
the
water
Transfers
thewater
Example
1. Aquifer yes Yes Sandy soil
2. Aquifuge No No Rock
3. Aquitard Partially Partially Silty Soil
4. Aquiclude Yes No Clay

Selection of watersources
• Quantity of water
• Quality of water
• Location
• Cost of water supply project
• Sustainable and safe
• Reliable

Thank you !!!
Sudip Khadka
Reference:
- Lecture Notes by Arun Prasad Parajuli
- P.N Modi
- B.C Punmia
- Various Google sites and Images
55
Visit:- sudipkhadka.com.np for more
notes and engineering materials

WaterSupplyEngineering
Prepared By:-Sudip Khadka
Engineering Student
Chapter 3: Quantity ofwater
Chapter- 3: QuantityofWater
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1

Content
1. Per capita demand of water
2. Design and base periods
1. Typical design and base periods
2. Selection basis
3. Design and base years
3. Types of water demand
1. Domestic demand
2. Livestock demand
3. Commercial demand
4. Public/municipal demand
5. industrial demand
6. Firefighting demand
4. Variationin demand of water
5. Peak factor
6.Factorsaffecting demand of
water
7. Population forecasting -
necessity and methods
1. Arithmetical increase method
2. Geometrical increase method
3. incremental increase method
4. Decrease rate of growth method
5.Numerical on population
forecasting and water demands
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Introduction: Quantity of Water
Why to study about Quantity of Water?
1. Toestimate the water demand for the community
2. Todesign the water supply system with long term benefits
3. Todetermine the capacity of the reservoir used in water supply
system
4. Tofind the suitable water resources that can meet the demand.
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Factors to be known before Designing WaterSupply System
Population
Base and
Design period
Per capita
demand of
water
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Per Capita Demand of Water
• Averagequantity of water consumption or waterdemand for various
purposes per person per day
• Usually expressed in liters per capita per day (lpcd)
• Per Capitademand in lpcd (q)= 𝑄
𝑃∗365
Where, Q= total quantity required per year in litresby city/ town
P= population of city/ town
• Water demands (liters/d)=Per capita demand (q) ×Population(P)
• It variesfrom person to person, place to place and time to time
• Per capita demand depends on:
• Standard of living
• Number and type of commercial areas
• Industry and climatic condition
• Quality of water
Chapter- 3: Quantityof Water
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Base and Design Periods:
Base period:
• Period required for the surveys, design and construction of a water supply system
• The base period of 2-3 years is normally adopted
Design Period:
• Number of years for which design of water works is carried out
• Future period for which a provision is made while planning and designing a water
supply project
• It is generally adopted as 15 to 20 years for rural water system and up to 30 years
for urban water system
• In communities with rapid development, low design period is adopted
• Should be realistic (neither long= financial overburden, nor Short= uneconomical)
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Selection Basis of DesignPeriod
Population
growthrate
Economical
development
Rate of
interest of
loan
Availability of
funds
Useful life of
components/
structures
Availability of
water
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1) Population Growth Rate:
 For high population growth rate shorter
design period is adopted and vice versa.
2) Development of Community:
 If the community is rapidly developing there
will be high population growth rate so
shorter design period is adopted.
3) Useful Life of Component Structures:
 The design period should not exceed the
useful life of the component structures
which depends on the quality and type of
materials used.
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4) Availability of Funds:
When limited funds are available shorter
design period is adopted and vice versa.
5) Rate of Interest on Borrowings:
If the money to be borrowed for a water
supply project is available at a lower rate of
interest, then a longer design period may be
economically justified and selected.
6) Availability of Water at Source:
When water available at the source is limited
shorter design period is adopted and vice
versa.
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Design and BaseYear:
Base Year:
The year in which water is actually delivered to the community by a water supply
system after the completion of its construction is known as base year
Survey year +Base period= Base year
Design Year:
The year for which a water supply system is designed is known as design year.
Base year +Design period =Design Year
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10

Question:
Should Water Supply System be designed only in the areas where there
is scarcity of Water or necessity to maintain the Water Demands?
The answer is No. Because water supply system doesn’t only helps to
maintain the water demands but also maintain the quality of water. It
helps to provide good quality of water suitable for drinking purpose
which is in accordance with WHO and National Drinking Water
Quality Standards
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Types of WaterDemand
Domestic demand
Livestock demand
Commercial demand
Public/ municipal demand
Industrial demand
Fire demand
Loss and wastage demand
Total water demand
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Domestic Water Demand
This includes the water requiredfor use in privateresidences apartment
houses.
• Drinking and cooking
• bathing and sanitary purposes
• washing of clothes, utensils, houses, etc.
Amount of waterconsumption depends upon:
 Living standard
 Habits
 Climatic conditions.
In Nepal, we use generallyuse following value:
 112 lcpd for fully plumbed houses
 65 lcpd for partly plumbed houses
 45lcpd for rural areas served by public stand posts.
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LivestockDemand
 Water consumed by domestic animals and birds
 Many of livestock utilize natural rivers, streams, and
ponds for the water during grazing.
 The livestock demand in Nepal is generally taken as
follows:
 Livestock demand should not be more than 20% of
domestic demand.
S.N. Types of animals Examples Demand
1 Big Animals Cow, Buffalo,Horse 45 litres/ animal/day
2 Medium Animals Sheep, Goat, Dog 20 litres/ animal/day
3 Small Animals Bird,Chicken, Ducks 20 litres/100 birds/day
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Question
Why is only 20% of domestic demand is considered for livestock
demand even if livestock demand>20% of domestic demand?
The reason behind this are:
 Many of the livestock will utilize natural rivers streams and ponds for water
during grazing.
 In urban areas the number of livestock is low and hence can be neglected.
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CommercialDemand
This includes the water demand of commercial establishment such as
educational institutions, offices, hotels, hospitals, restaurants, etc.
 The quantity of water required for this purpose will vary
considerably with nature and type of the commercial establishments.
The commercial demand should be considered for water supply
systems in both the rural and the urban areas.
The reason behind this is the presence of commercial establishments
both in rural and urban areas.
It covers 5-10% of total demand.
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The commercial water demand in Nepal is generally taken as:
S.N. Type Demand/day
1 Hospitals
i. With bed
ii. Without bed
500litres/bed
2500litres
2 School
i. Boarders
ii. Day scholar
65litres/pupil
10 litres/pupil
3 Hotel
i. With bed
ii. Without Bed
200litres/bed
500-1000 litres
4 Restaurants/ teastalls 500-1000 litres
5 Office 500-1000 litres
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Public/MunicipalDemand
This includes the water required for public or municipal utility
purposes.
A provision of 5 to10 % of total consumption is made for these
demands
Only considered in urban water supply system
S.N. Type Demand/day
1 Street washing 1-1.5litres/m^3
2 Sewer cleaning 4.5litres/ head
3 Parks 1.4litres/ m^3
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Uses:
 Washing and sprinkling on road
 Cleaning sewers
 Watering public parks/ gardens
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IndustrialDemand
It represents the water consumed by
the industries.
For a city with fans and factories, a
provision of 20 to 25% of total
consumption may be made for this
purpose.
The forecast for this demand will be
based on nature and magnitude of each
industry and the potential for its
expansion.
Considered for urban communities only.
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20

FireDemand
Quantity of water required for fire fighting purpose.
Provision should be made in modern public water supply
Water head is 10-15m of water
Diameter of pipe ranges from 10 to 15 cm
Demand is mostly for:
 Short circuiting
 Fire catching materials
 Explosion
 Bad intentional crimes
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FireDemand
Fire Demand is usually determined by using empirical formula:
1. Indian water supply manual and treatment formula
Q(kiloliters/day)=100√P
2. Buston's Formula
Q(liters/min)=5663√P
3. Kuichling’s Formula
Q(liters/min)=3182√P
4. Freeman’sFormula
Q(liters/min)=1136(P/5+10)
5. National Board of FireUnderwriters’ Formula
Q(liters/min)=4637√P(1-0.01√P)
Where, Q= Quantity of water
P= Population of service area in thousands
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Fire Demand(Continued…)
• DWSS design guideline recommends
Indian Water Supply Manual and
Treatment Formula in Nepal for the
determination of the water required for
the fire fighting purpose.
• Guideline recommends that Fire demand
should be less than one lpcd.
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Numerical
Calculatethe water required for firedemand in a city of population 100,000
using various formulae.
Solution:
Given; P=population in thousands=100
1. Indian water supply manual and treatment formula
Q= 100√P =100√100
=1000 kiloliters/day
2. Buston's Formula
Q=5663√P
Q=5663√100
=56630 liters/min
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3. Kuichling’s Formula
Q=3182√P =3182√100
=31820 liters/min
4. Freeman’s Formula
Q(liters/min)=1136(P/5+10)
=1136(100/5+10)
=34080liters/min
5. National Board of Fire Underwriters’ Formula
Q= 4637√P(1- 0.01√P)
=4637√100(1- 0.01√100)
=41733liters/min
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Loss and Wastage ofWater
Cause:
 due to leakage in mains, valves and other fittings,
worn or damaged meters,
theft of water through the various unauthorized connections, etc.
Cannot be precisely predicted.
Only considered in urban communities as the allowance for it has been
already made in domestic demand for ruralwater supply system.
In general,waterloss occurs at the following ways:
S.N. WaterSupply System Water Loss
1 Well maintained and fully metered supply 15% of total supply
system
2 Partly metered and partly unmetered water Up to 50% of total
supply system system
Chapter- 3: Quantityof Water
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Total waterDemand
Total Water Demand (TWD):
27

Minimum
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Variation in Demands ofWater
1. Seasonal variation
2. Hourly variation
3. Daily variation
4. Monthly variation
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Seasonal Variation
The rate of demand of water varies from season to season.
In summer people use more water compared to winter.
In Nepal, the variation in rate of demand due to season is very low, so
the seasonal variation is generally neglected in Nepal.
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑠𝑒𝑎𝑠𝑜𝑛𝑎𝑙 𝑑𝑒𝑚𝑎𝑛𝑑
= 𝑠𝑒𝑎𝑠𝑜𝑛𝑎𝑙 𝑝𝑒𝑎𝑘 𝑓𝑎𝑐𝑡𝑜𝑟 ∗ 𝑎𝑛𝑛𝑢𝑎𝑙 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑚𝑎𝑛𝑑
The seasonal peak factor is assumed as 1 in Nepal
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HourlyVariations
 Demand varies from hour to hour.
Demand is more in the morning and evening due to washing,
cleaning, bathing etc.
Maximumhourlydemand
=Hourlypeakfactor*Annualaveragedemand
The hourly peak factor of 2 to 4 is adopted in Nepal while the hourly
peak factor of 1.5 is generally adopted in India.
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Daily Variations
The demand of water varies from day to day.
This is due to change in the day to day climatic conditions, or due to
the festival day or due to the day being holiday.
The rate of demand on Saturday is more than other days because
more water is used for washing, bathing, etc.
Similarly, the rate of water demand will be more on festival day than
other days.
Maximumdailydemand
=Dailypeakfactor*Annualaverage demand
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MonthlyVariations
 Demand varies from month to month.
Monthly variation is not considered in Nepal.
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PeakFactor
Peak factor is the ratioof maximum or peak demand of water to that of
annual averagedemand of water.
𝑄 𝑝 𝑒𝑎 𝑘/𝑚 𝑎𝑥 𝑖𝑚 𝑢𝑚
Peak factor(PF) =
𝑄𝐴𝑣𝑒𝑟𝑎𝑔𝑒
In other words,the maximum or peak demand of water is calculated
multiplying the annual averagedemand of water by the peak factor.
𝑄𝑝𝑒𝑎𝑘/𝑚𝑎𝑥𝑖𝑚𝑢𝑚 = Peak factor PF ∗𝑄𝐴𝑣𝑒𝑟𝑎𝑔𝑒
For continuous distribution, PF= 2-4
For intermittentdistribution, PF=4-6
Peak factor= Seasonal peak factor * Daily peak factor * Hourly peakfactor
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Factors Affecting Demand ofWater
Size and type of community
Climatic conditions
Standard of living
Quality ofwater
Systemof supply
Pressure in the distribution system
Sewerage System
Metering
Cost of water
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Size and Type ofCommunity
In general, bigger is the
community, higher is the
demand of water
Large quantity of water is
required for public or municipal
purposes
Small community has less per
capita consumption of water
because there are limited uses.
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Climatic Conditions
Requirement of water is more in summer
than in winter.
Water requirement is more in communities
having hot and dry climates than in
communities having cold climates
Used for washing, bathing, air conditioning,
etc in communities with hot and dry climate
Taps are kept open to avoid the freezing of
pipes which increases the rate of
consumption.
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Standard ofLiving
Higher the standard of living,
greater the water demand
because people can afford luxury
and use more water.
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Quality ofWater
Water consumption will be more if the quality of water supplied is
good
Consumers will feel safe to use water and use it liberally
System of WaterSupply
 Two types of water supply system
 Continuous system
 Intermittent system
 Water demand is less in intermittent system due to limited water, storage requirement.
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Pressure in the DistributionSystem
Higher in the pressure,
loss of water is more
and demand is high
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Sewerage System
Sewerage system increases water demand.
Water is required for: flushing urinals, cleaning closets
Chapter- 3: Quantity ofWater
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Metering
Meters are fitted at the head of the individual house connections, which records
the quantity of water consumed.
 Consumption is less if consumers are charged for water consumed.
 To check loss and leakage of water.
 Also reduces water demand
44

Cost of Water
Higher the cost of water, less
is the demand of water
In Pokhara Valley, the
average cost of water is 15
per unit
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Population Forecasting
What is Forecasting?
Forecasting is the process of making
predictions of the future based on past and
present data and most commonly by
analysis of trends.
Forecastinghas applicationsin a wide range
of fields where estimatesof future
conditionsareuseful.
Not everything can be forecastedreliably, if
the factorsthat relateto what is being
forecast are known and well understood.
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Significance of populationforecasting
• Population of a certain area , either town or a village is always a
dynamic parameter. So, one need to consider the future demand of
water, most often the greater one, so as to avoid the subsequent
changes in water supply system that needs to be considered for a
dynamic population which may be uneconomic and unsustainable.
• Tocalculate water demand for present as well as future requirements.
• Information about the population of a city or town is obtained from
census.
• Census is conducted at an interval of 10 years.
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Factors affecting population growth rate
Birth rate
Death rate
Migration
Community life
Communication and information
Tourism
Unforeseen Factors
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Method Of Population Forecasting
1. Arithmetical Increase Method
2. Geometrical Increase Method
3. Decreased Rate Of Growth Method
4.Incremental Increase Method
Some other methods are:
5. Simple graphical method
6. Comparative Graphical Method
7. Master Plan Method
8. Logistic Curve Method
9. The AppropriateMethod
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Arithmetical Increase Method
Simplest method of population forecast that gives lower results.
 Increase in population from decade to decade is assumed constant.
Generally adopted for largeand old cities which have practically reached
their maximum development.
The future population 𝑃𝑛after n decades is given by the expression given
below.
𝑃𝑛= 𝑃0 + nC
Where, 𝑃𝑛= future population at the end of n decades
𝑃0= present population/ last known population
C = averageincreasein population for a decade
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Numerical
Estimate the population of a town for design year 2098 by arithmetical
increase methods. The census data are as follows.
Year Population
2038 8000
2048 12000
2058 17000
2068 22500
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Here, 𝑃0= present(2068) population = 22500
C = average increase in population per decade =
4000+5000+5500
3
= 4833
n = 2098−2068
= 3
10
We have, 𝑃𝑛= 𝑃0+ nC
𝑃2098= 22500 + 3*4833
= 36999
Year Population Increase in
population
2038 8000
2048 12000 12000-8000=4000
2058 17000 17000-12000=5000
2068 22500 22500-17000=5500
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Geometrical Increase Method
 Gives higher results.
 Percentage increase in population from decade to decade is assumed constant.
Generally adopted for new industrial town at the beginning of development for
only few decades.
 The future population 𝑃𝑛after n decades is given by the expression given below.
𝑛 0 100
𝑃 = 𝑃 (1 +
𝑟
)𝑛
𝑃0= present population
r = average percentage increase in population per decade
r =
𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑖𝑛 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
∗ 100
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
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Numerical
Estimate the population of a town for design year 2098 by geometrical
Year Population
2038 8000
2048 12000
2058 17000
2068 22500
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n =
2098−2068
= 3
50+41.7+32.4
3
=41.37%
We have, 𝑃𝑛= 𝑃0(1 + )
10
r = average % increase in population per decade =
𝑟 𝑛
𝑃2098=𝑃2068(1 +
100
)
100 𝑟 𝑛
2098 100
)
𝑃 = 22500(1 +
41.373
𝑃2098=63570
Year Population Increase in population % increase in population
2038 8000
2048 12000 12000-8000=4000 4000
8000
∗ 100 = 50
2058 17000 17000-12000=5000 5000
12000
∗ 100 =41.7
2068 22500 22500-17000=5500 4000
8000
∗ 100 = 32.4
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Incremental IncreaseMethod
Gives average results.
Suitable for an averagesize town under normal condition where the growth rate
is found to be in increasing order.
Incremental increase in population from decade to decade is calculatedwhich
may be either positive or negative.
The future population 𝑃𝑛after n decades is given by the expression given below.
n(n + 1)
2
𝑃𝑛 = 𝑃0 + nC + i
C = averageincrease in population per decade
i = averageincremental increase
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Numerical
Estimate the population of a town for design year 2098 by incremental
Year Population
2038 8000
2048 12000
2058 17000
2068 22500
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n = 2098−2068
= 3
10
C = average increase in population per decade =
4000+5000+5500
3
= 4833
i = average incremental increase in population per decade =
1000+500
2
= 750
2
We have, 𝑃𝑛= 𝑃0+ nC +
n(n + 1)
i
2
𝑃2098= 𝑃2068+ nC +
n(n + 1)
i
2
𝑃2098= 22500 + 3*4833 +
3(3 + 1)
750
𝑃2098=41499
Year Population Increase in population Incremental increase in population
2038 8000
2048 12000 12000-8000=4000
2058 17000 17000-12000=5000 5000 −4000 = 1000
2068 22500 22500-17000=5500 5500 −5000 = 500
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DecreasedRate of Growth Method
Also known as changing rate of increase method.
Decreasing value of the percentage increase in population from
decade to decade is assumed to be constant.
The future population 𝑃𝑛after n decades is given by the expression
given below.
𝑛 0
𝑃 =𝑃 (1 + 𝑟−1𝐷
) 1 + 1 +
100 100 100
𝑟 −2𝐷 𝑟 −3𝐷
𝑟 −𝑛 𝐷
… . (1 + )
100
Where , 𝑃𝑛= future population at the end of n decades
r = percentage increase in population in the last decade
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Numerical
Estimate the population of a town for design year 2098 by incremental
Year Population
2038 8000
2048 12000
2058 17000
2068 22500
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n = 2098−2068
= 3
10
r = % increase in population in last decade = 32.4
−8.3−9.3
2
D = average decrease in % increase in population per decade = =-8.8%
𝑛 0
We have, 𝑃 =𝑃 (1 +
𝑟−1𝐷
) 1 +
𝑟−2𝐷
100 100 100 100
1 + 𝑟−3𝐷
… . (1 +𝑟−𝑛𝐷
)
𝑃 =𝑃
2098 2068 (1 + 𝑟−1𝐷
) 1 + 𝑟−2𝐷
1 + 𝑟−3𝐷
100 100 100
𝑃2098 100
=22500(1 + 32.4+8.8
)1 + 32.4+2∗8.8
1 + 32.4+3∗8.8
100 100
𝑃2098=75676
Year Population Increase in population % increasein popln Decreasein % increase in popln
2038 8000
2048 12000 12000-8000=4000 4000
∗ 100=50
8000
2058 17000 17000-12000=5000 5000
∗ 100=41.7
12000
41.7-50=-8.3
2068 22500 22500-17000=5500 4000
∗ 100=32.4
8000
32.4-41.7=-9.3
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Numerical
Estimate the population of a town for design year 2050 AD by all four
methods. The census data are as follows.
Year Population
1990 40000
2000 45000
2010 55000
2020 62000
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Numerical Example

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Thank you !!!
Reference:-
- LectureNotesby ArunPrasadParajuli
- LectureSlidesby Er.Sabina Paudel
- P.NModi
- B.C Punmia
- VariousGooglesitesandImages
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Visit:- sudipkhadka.com.np for more
engineering notes and tutorials

PreparedBy:-Sudip Khadka
Engineering Student
Chapter 4: Quality ofwater

Content
• Impurities in water, their classificationand effects (suspended/ colloidal/
dissolved)
• Hardness and alkalinity(types, relationsand numerical)
• Living organism in water (Algae, Bacteria, Viruses, worms)
• Water related diseases
• Examination of water ( Physical,Chemical, Biological)
• Water quality standards for drinking water

Types ofWater
 Pure and impure water:
 Pure: Chemically pure, combination of
two parts of hydrogen, 1 part of oxygen
 Impure: two parts of hydrogen, 1 part of
oxygen with extra elements like salt,
minerals etc.
 Polluted and contaminated water
 Polluted: Water which contains harmful
substances, but does not contain pathogens
 Contaminated : Polluted water which contains
pathogens (disease containing bacteria)

Introduction
Water quality is the physical, chemical and
biological characteristics of water.
It is the measure of the condition of water
relative to the requirement of one or more
biotic species and or to any human need.
Parameters for water quality are determined
by the intended use:
 Human consumption
 Industrial use
 environment

Impurities in water
When we talk about impurities found in water,
we're typically referring to
the negative components dissolved in water.
These impurities in water are what we seek to
exclude from drinking water.
The types of impurities in water can include dust,
dirt, harmful chemicals, biological contaminants,
radiological contaminants, and total suspended
solids (TSS).
Total suspended solids are visible particles that can
make water appear cloudy or hazy.

Classification of impurities(State)
1. Suspended impurities
2. Dissolved impurities
3. Colloidal impurities

SuspendedImpurities
 Impurities which normally remain suspended
 They make water turbid, so are tested by turbidity test.
 They are removed by sedimentation or filtration.
 Effects:
Causes turbidity, diseases, foul odour
 Examples:
Sand, silt, clay, algae, fungi, floating leaves etc.

DissolvedImpurities
 Impurities which are not visible, but are dissolved
 These impurities generate foul smell, hardness and alkalinity
 They are mostly minerals and salts which are soluble in nature.
 Measured by: evaporation
 Treatment: distillation, precipitation, adsorption or extraction
 Effects: foul smell, hardness and alkalinity
 Example:
invisible organic compounds, inorganic salts and gases

Colloidal Impurities
These impurities are electrically charged, small particles which are unstable in
nature
These impurities are so small that they are not visible to naked eye and cannot be
separated by ordinary filters.
 Measured by: colour test
 Removed by: neutralization, chemical coagulation, sedimentation and filtration
 Effects: colour, acidity, produces bacteria
 Example:
organic matters containing bacteria

Classification of impurities(Characteristics)
1. Physical impurities:
Impurities that affect the physical characteristics of water such as colour, taste,
odour. The presence of these impurities makes water objectionable to drink.
Eg: algae, organic matter, sewage etc.
2. Chemical impurities:
Impurities which affect the chemical characteristics of water such as suspended
and dissolved solids, pH, hardness etc. its excess may lead to diseases when
consumed.
3. Bacteriological impurities:
Impurities which affect the bacteriological characteristics of water such as
pathogen and non-pathogenic microorganism.

Hardness and Alkalinity
Hardness:
 Characteristics of water which prevents the formation of sufficient lather.
It is due to presence of bicarbonates, sulphates, chlorides and nitrates of calcium,
magnesium and strontium.
 Effects of hardness:
 Hard to form lather so consume more soap
 Forms large scale of boilers
 Modifies colour in the dyeing industries
 Causes corrosion in pipes
 Makes food tasteless

Types ofHardness
 Temporary Hardness:
Hardness due to presence of bicarbonates of
calcium , magnesium and strontium
 Removed by: boiling
 Also known as carbonate hardness.
 Permanent Hardness:
Hardness caused by the presence of sulphates,
chlorides and nitrates of calcium, magnesium
and strontium
 Removed by: lime soda and zeolite method
 Also known as non-carbonate hardness

Determination ofHardness
Expressed in ppm or mg/l of 𝐶𝑎𝐶𝑂3 present inwater
3
Hardness in mg/l as 𝐶𝑎𝐶𝑂 =ion concentration ∗ 𝐸𝑄.𝑊𝑇.𝑜𝑓 𝐶 𝑎 𝐶
3
𝐸𝑄.𝑊𝑇.𝑜𝑓 𝑖𝑜𝑛
 𝐸𝑄. 𝑊𝑇.𝑜𝑓𝐶𝑎𝐶𝑂3=50
 𝐸𝑄. 𝑊𝑇.𝑜𝑓𝐶𝑎++=20
 𝐸𝑄. 𝑊𝑇.𝑜𝑓𝑀𝑔++=12.2
 𝐸𝑄. 𝑊𝑇.𝑜𝑓𝑆𝑟++= 43.8

Alkalinity:
It is a measure of ability of water to neutralize acid
It is due to the presence of those substances in water which has the
tendency to increase the concentration of 𝑂𝐻− 𝑖𝑜𝑛𝑠
pH >7
3 3
Alkalinity in water is due to presence of 𝐻𝐶𝑂−, 𝐶𝑂−− and 𝑂𝐻−

Determination ofalkalinity:
 Expressed in ppm or mg/l of 𝐶𝑎𝐶𝑂3
 Carbonate alkalinity in mg/l as 𝐶𝑎𝐶𝑂3 = 3
C𝑂−−ion concentration
0.6
 Bicarbonate alkalinity in mg/l as 𝐶𝑎𝐶𝑂3 = 3
𝐻𝐶𝑂−ion concentration
1.22
3
 Hydroxide alkalinity in mg/l as 𝐶𝑎𝐶𝑂 =
−
𝑂𝐻 ion concentration
0.34
 Hydroxide alkalinity and Bicarbonate alkalinity do not exist in the water together.
 Total Alkalinity= Carbonate alkalinity + Bicarbonate alkalinity
 Total Alkalinity= Carbonate alkalinity + Hydroxide alkalinity

Relation between hardness andalkalinity
When Total Hardness (T.H)> Alkalinity
 Carbonate Hardness (C.H)=Alkalinity, and
 Non-Carbonate Hardness (N.C.H) =T.H – C.H
= T.H - Alkalinity
When Total Hardness (TH)≤Alkalinity
 C.H = T.H
 N.C.H = 0

Numerical
The analysis of water from a well showed the following results in mg/l.
𝑁𝑎+ = 20.5 𝑀𝑔++ = 30 𝐶𝑎++=90 𝐾+=21.5
𝐶𝑙− = 40 𝐻𝐶𝑂− = 92
3 4
𝑆𝑂−−=22.8 𝑁𝑂−=12 𝐶𝑂−−=102
3 3
The concentration of strontium(Sr) is equivalent to the hardness of 25.52mg/l.
Calculate the carbonate hardness, non-carbonate hardness and total hardness.

Numerical
The total hardness value obtained from the analysis of water sample is found to be
230mg/l. The analysis further showed the hardness has been caused by calcium and
magnesium ions only and their concentrations are numerically same. If the value of
carbonate hardness is 90mg/l and alkalinity in water is caused by bicarbonate ions
only. Calculate the following:
i. Value of non-carbonate hardness
ii. Concentration of calcium and magnesium ions
iii. Concentration of bicarbonate ion in mg/l

Numerical
The total hardness value obtained from the analysis of water sample is found to be
280mg/l. The analysis further showed the hardness has been caused by storntium,
calcium and magnesium ions only and their concentrations are numerically same. If
the value of carbonate hardness is 110mg/l and alkalinity in water is caused by
carbonate ions only. Calculate the following:
i. Value of non-carbonate hardness
ii. Concentration of calcium and magnesium ions
iii. Concentration of bicarbonate ion in mg/l

Living Organisms inwater
Algae Bacteria Viruses Worms

Water Related Diseases
• Transmission route

Examination ofWater
• Physical parameters
• Chemical parameters
• Bacteriological parameters

Physical Parameters
Turbidity
Colour
Taste
Odor
Temperature
Radio active substances(Conductivity)

Turbidity
Turbidity in the water indicates presence of:
 Suspended or colloidal insoluble matter including coarse
particles (mud, sediment, sand, clay,siltetc
 Decayed vegetational matter
 Algae, fungi, bacteria, protozoa etc.
Turbidity is expressed as the amount of suspended matter
in mg/l or ppm.
The standardunit is that which is produced by 1 milligram
of finely divided silica in 1litre of distilled water.
Permissible limit=5-10 ppm. (>5ppm= visible to naked eye)
Removed by: settling, coagulation and filtration.
Measured by:
 Turbidityrod
 Baylis instrument
 Jacksons turbidity
 Nephelometers

1. Turbidity Rod
Used in field
The turbidityis measured directly
by reading the graduationin the
aluminum rod on the surface of
water.
More the length, lesser the
turbidityand vice-versa.
Procedure:
 Fill the container with sample raw
water
 Insert the graduated glass tube and
look through for the platinum needle
 Keep inserting the tube till you stop
seeing the needle
 The corresponding reading at that
point is the turbidity for the sample.
Nonstretchable
1 mm dia, 25 mm long

2. Jackson’s Turbidimeter
JTU: Jackson’s Turbidity Unit
Measures turbidity> 25mg/litre
Procedure:
 Lit the candle
 Fill the container with sample raw
water
 Insert the graduated glass tube and
look through for the light flame
 Keep inserting the tube till you stop
seeing the flame
 The corresponding reading at that
point is the turbidity for the sample.

3. Baylis Turbidimeter
 Colour matching technique
 Measures turbidity upto 2ppm
 Unit: BTU
 Procedure:
Fill the 1st test tube with sample raw water
for which you need to calculate turbidity and
2nd test tube with a known turbidity water
sample
Lit the 250watt electric bulb which will be
reflected by the reflector placed behind
Match the colour of sample and known
sample
If color does not match change the known
sample with another known sample of
different turbidity
Continue until you get the same colour in
both test tube
The corresponding turbidity of known
sample at that point is the turbidity for the
sample.

4. Nephelometers
Very precise,measure turbidity of the order
of 0-1ppm
It is based on the principle of scatteringof
light
Procedure:
 In this instrument, the sample scatters the light
that impinges on it.
 The scattered light is then measured by putting
the photometer at right angle to the original
direction of the light generated by the light
source.
 This measurement of light scattered at right
angle is called “Nephelometry”.
 Unit of turbidity: NTU “Nepholmetric turbidity
unit”

Color:
 It is usually due to organic matter in colloidal condition, or
due to minerals and dissolved organic impurities.
 Permissible color: 20ppm
 The standard unit of colour is that colour which is
produced by 1 mg of platinum cobalt in the form of
chloroplatinate ion.
 Color can be detected by naked eye.
 It can be measured by comparing the colour of sample
water with other standard glass tube called “Nessler’s
tubes”
 Most precise instrument: tintometer
 Colour of water is not harmful but is objectionable.
 Yellowish color indicates the presence of chromium and
appreciable amount of organic matter.
 Yellowish red color indicates the presence of iron
 Red brown color indicates the presence of peaty matter.

Measurement ofcolour
Nessler Tubes:
Measured by comparing the
colour of raw sample with
the other standard glass
tubes containing solution of
different standard of colour
intensities.
Tintometer:
Precise measurement
For precise measurement of small colour intensities, compact
instrument properly lighted from inside is used.
The instrument contains an eye piece with two holes.
A slide of standard coloured water is seen through one hole and
slide of raw sample from other hole.
The standard coloured slide is replaced by another until a
matching slide is found.

Taste:
 It is due to the presence of:
 Dissolved mineral
 Dissolved inorganic salts
Bitter taste: presence of iron, aluminum,
manganese, sulphate or lime.
Soapy taste: presence of large amount of
sodium bi carbonate.
Brackish(slightly salty, unpalatable) taste :
presence of unusual amount of salts.
Palatable(acceptable taste) Taste: presence
of dissolved gases and minerals like nitrates
in water.

Odour:
 Odour is due to:
 Dissolved gases, chlorine, hydrogen, sulphide etc.
 Dissolved organic vegetational matter
 Waste products discharge from industries.
Both taste and odour are inseparable and are measured by same scale “Threshold
Odour Number (TON)”
TON =
𝐴+𝐵
𝐴
where, A= volume of raw water sample
B= volume of distilled water sample which is used for dilution
 Permissible value of TON=1-3
 Now a days, odour is measured by a sensitive instrument “Osmoscope”

Temperature:
Temperature of water supplied should be
between 10-20 ͦC. Temperature greater than
25 ͦCis highly objectionable.
 Measured by: “Ordinary thermometer”
graduated in 0.1ͦC
In case of large bodies of surface water:
“Broken capillary thermometer” is used to
measure at different depth
In addition to its own effects, temperature
influences several other parameters and can
alter the biological and chemical properties of
water.
An increase in temperature of 10 ͦC, doubles
the biological activity.

Conductivity:
The total amount of dissolved salt present in
water is measured by the specific conductivity of
water.
 Determined by: portable dionic water tester
expressed in “ micro-mhos per cm” at 25 ͦC
Dissolved salt= specific conductivity of water *
coefficient(0.65)
The exact value of coefficient depends upon the
type of salt.
 More salinity refers to more conductivity
 Permissible value: nil

ChemicalParameter
 Solids: Total Solids & Suspended Solids
 pH value of water
 Alkalinity
 Hardness of water
 Presence of different chemical compounds
 Chloride Content
 Nitrogen Content
 Sulphur Content
 Metals & other Chemical Substances
 Dissolved Gases
 Biochemical Oxygen Demand ( BOD )

Solids
Total solids=
 Solids present in water can be either dissolved solids or suspended solids.
 Solids are expressed inmg/l
Wt. residueafter evaporation(mg)−𝑊𝑡 𝑜𝑓 𝐵𝑒𝑎𝑘𝑒𝑟
Volume of water ( ml)
Total solids= Suspended solids+ Dissolved solids
Suspended solids=
Wt. residueon filter paper(mg)−𝑊𝑡𝑜𝑓 𝑓𝑖𝑙𝑡𝑒𝑟 𝑝𝑎𝑝𝑒𝑟
Volume of water ( ml)
Dissolved solid= total solid- suspended solid
 Permissible amount of total dissolved solids in water = 500ppm -1000ppm

Presence of different chemicalcompounds
 Chloride Content
 Nitrogen Content
Sulphur Content
Metals & other Chemical Substances
 Dissolved Gases

Chloride Content
Chloride in water are derived mostly from natural mineral deposits, agricultural
discharges
Higher concentration of chloride indicates to pollution of water due to sewage or
industrial water
 Permissible value of chloride< 250ppm
 If we consume more chlorinated water it leads to indigestion/metabolic disorders
 They are estimated by Mohr’s method:
 Raw water is titrated with standard Silver Nitratesolution
 Chlorides are precipitated as white silver chloride
 Using Potassium Chromate as indicator, which supplies chromate ions

Sulphate Content
• Are due to industrial effects
• Presence of sulphate beyond permissible limit leads to laxative effects
• Permissible limit< 250ppm
Lead & ArsenicContent
• Presence of lead & arsenic is very harmful to human health
• Leads to accumulation of toxins in the body tissue
• Permissible limit= nil

Ferrous & MaganeseContent
 Leads to decolourization of clothes, appearance of stains
 Permissible value: Fe<0.3ppm
Mn>0.05ppm
Fluoride Content
 Can be removed by reverse osmosis filtration system
 Permissible value:1-1.5ppm
 1ppm= saves from dental cavity
 >1.5ppm= decolourization of teeth of babies(motting of teeth)
 >1.5ppm= weakening of bones (bone fluorosis)

NitrogenContent
Indicates the presence of organic matter
Presents in various forms:
 Free ammonia
 Organic nitrogen
 Nitrites
 Nitrates
Free ammonia:
 First stage of decomposition (recent pollution)
 Can be measured by simply boiling of water and measuring the amount of ammonia
liberated by distillation process
 Permissible value< 0.15mg/l
Organic nitrogen
 It indicates pollution, quantity of nitrogen before decomposition has started
 Measured by boiling of already boiled water and adding strong alkaline solution like
potassium permanganate till ammonia gas is liberated, which is measured
 Permissible value< 0.3mg/l

Nitrites:
 It indicated partly decomposition condition
 It is highly dangerous
 Permissible value: nil
 Measured by colour matching technique
 The colour of nitrite is developed by sulphonic acid and napthamine
Nitrates :
 It represents fully oxidized organic matter, old pollution
 Permissible value< 45mg/l
 The presence of too much nitrates in water adversely affect the health of
infants causing a disease called “mathemoglobinemia” or “blue baby disease”
 Measured by colour matching technique
 Colour is developed by phenol-di-sulphonic acid and potassium hydroxide

Dissolvedgases
Mainly hydrogen sulphide, carbon dioxide, methane, nitrogen and
dissolved oxygen
 Hydrogen sulphide leads to foul smell and bad taste
 Methane has explosive tendency
 Carbon dioxide imparts bad taste and water becomes corrosive. It also
indicates biological activity
 So their permissible value is nil.
Dissolved oxygen:
 It is a measure of how much oxygen is dissolved in the water or the amount
of oxygen available to living aquatic organisms.
 Permissible value: 5-10 ppm

Biochemical OxygenDemand
The amount or demand of oxygen that is required for the complete
consumption of biodegradable organic matter.
Permissible value: nil
It is tested for both raw water and treated water

pH value ofwater
pH value denotes the concentration of hydrogen ions in the
water and it is a measure of acidity or alkalinity of a substance.
𝑝𝐻 = −𝑙𝑜𝑔[𝐻+], [𝐻+] = ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝑖𝑜𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑚𝑜𝑙𝑒𝑠/𝑙
𝑃𝑂𝐻 = −𝑙𝑜𝑔[𝑂𝐻−], [𝑂𝐻−] = ℎ𝑦𝑑𝑟𝑜𝑥𝑦𝑙 𝑖𝑜𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑚𝑜𝑙𝑒𝑠
𝑙
𝑝𝐻 + 𝑃𝑂𝐻 = 14
[𝐻+] + 𝑂𝐻− = 10−14
pH = 0 − 7, acidic
pH = 7, Neutral
pH = 7 − 14, Alkaline
 pH is measured by: “Potentiometer”
 Permissible limit of pH= 6.6 to 8.5
 𝑤ℎ𝑒𝑛, [𝐻+]𝑖𝑠 𝑚𝑜𝑟𝑒 𝑝𝐻 𝑣𝑎𝑙𝑢𝑒 𝑤𝑖𝑙𝑙 𝑏𝑒 𝑙𝑒𝑠𝑠 𝑎𝑛𝑑 𝑣𝑖𝑐𝑒𝑣𝑒𝑟𝑠𝑎.
 Less pH will make water acidic, resulting corrosion and also
digestion problem.

pH can also be detected by using colour indicator;
• Methyl orange indicator
• Phenolphthalein
Indicator pH range OriginalColour of
indicatordye
Final Colour
Methyl Orange 2.8-4.4 Red Yellow
Phenolpthalein 8.6-10.3 Yellow Red

BacteriologicalParameter
The concentration of coliforms present in water are tested instead of pathogens,
as pathogens are present in small numbers and their testing is time consuming as
well as expensive.
 The coliforms should be nil in drinking water.
 Methods of determining coliforms:
1. Multiple tube fermentation technique(Most probable number (MPN))
2. Membrane filter fermentation
3. Coliform index test:
The reciprocal of smallest quantity of the sample that gives the positive B-coli test.

Multiple tube fermentationtechnique
It requires the use of multiple number of standard fermentation
tubes(Durham Tubes) for the determination of coliform group of
bacteria.
Three tests:
i. Presumptive test
ii. Confirmatory test
iii. Completed test

Presumptive test
 Take 10 ml of raw sample in a test tube.
 Take three test tube of 10 ml with each being filled with 9 ml of distilled water.
 The first test tube is then added with 1ml of raw water making it a 1ml dilution sample.
 Take the second test tube and add 1ml of 1ml dilution sample making it a 0.1ml dilution
sample.
 Take the third test tube and add 1ml from 0.1ml dilution sample making it 0.01ml
dilution sample.
 Make 5 test tubes each of 10ml, 0.1ml and 0.01ml dilution.
 Add lactose broth to all and incubate them in an incubator at 35degree celcius for 48
hours for the production of gas.
 Result:
 Gas produced: positive test ; contains coliform bacteria
 Gas not produced :negative test; absence of coliform bacteria (discarded further)

ConfirmedTest
All the positive test samples are now transformed to other fermentation tubes
containing brilliant green bile broth.
Incubate the tubes at 35 degree Celsius for 24-48 hours for gas production.
(carbon dioxide gas)
 At the end of test , observe the gas production.
 Result:
 Gas produced: positive test; confirms the presence of coliform group of bacteria
Gas not produced : negative test; confirms the absence of coliform group in
water (discarded further)

CompletedTest
It is conducted to demonstrate with certainty that the positive test results from
two previous test actually contains coliform bacteria.
The positive samples from confirmatory test are placed in a plate with Endo or
Eosin methylene blue agar.
Incubate at 37 degree Celsius for 24 hours till colonies of coliform bacteria are
formed.
Pick up discrete isolated colonies of bacteria from the plate and carefully transfer
to fermentation tubes containing lactose broth.
 Incubate at 37 degree Celsius for 24 hours for gas production.
 Result:
 Gas produced: positive test; confirms the presence of coliform group of bacteria
Gas not produced : negative test; confirms the absence of coliform group in
water

Most probable number(MPN)
The number of coliforms present in water is expressed
as MPN.
MPN is defined as that bacteria density which is most
likely to be present in water sample
The standard samples of five sets of each 10ml, 0.1 ml
and 0.01 ml which were taken are analyzed and finally
conformed positive test for each dilution are recorded.
Based on the sequence MPN is determined from the
MPN table developed on the law of statics and
probability.

MPN/100ml=
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑜𝑠𝑖𝑡𝑖𝑣𝑒 𝑡𝑢𝑏𝑒𝑠
𝑚𝑙 𝑜𝑓 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒 𝑡𝑢𝑏𝑒𝑠∗𝑚𝑙 𝑖𝑛 𝑎𝑙𝑙 𝑡𝑢𝑏𝑒𝑠
∗100

Membrane filterfermentation
Recent method to detect the coliform group of bacteria and measuring theirconcentration.
Procedure:
Take a raw sample of water containing certain amount of bacteria.
Take a sterilemembrane filter having porosity of 80% with microscopic pores of size 5 to 10 m𝜇.
Keep this membrane in a filter paper in the funnel fitted with vacuum pump.
Filter the raw sample through this.
Take out the membrane from the funnel and put it in the plate containing M-Endo medium as nutrient. M-
Endo medium inhibits the growth of other bacteria other than coliform group.
Incubate the plate at a temperature of 37 degree Celsius for 20 hours.
At the end of the incubation period, the bacteria of coliform group if present in the water are developed
into visible colonies.
Count the number of colonies with the help of microscope.
Coliform colonies/100ml=
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑜𝑙𝑖𝑓𝑜𝑟𝑚 𝑐𝑜𝑙𝑜𝑛𝑖𝑒𝑠 𝑐𝑜𝑢𝑛𝑡𝑒𝑑
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑎𝑤 𝑠𝑎𝑚𝑝𝑙𝑒
∗ 100

Water Quality Standard for drinkingpurpose
The maximum concentration of impurities in water at which it is not harmfulto human health and
water can be supplied safely is termed as standard.
The standard for various types of water quality parameters are known as waterquality standard.

Thank you !!!
Reference:-
- LectureNotesby ArunPrasadParajuli
- LectureSlidesby Er.Sabina Paudel
- P.NModi
- B.C Punmia
- VariousGooglesitesandImages
Chapter- 4: Quality ofWater
Sudip Khadka
Visit:- sudipkhadka.com.np for more notes
and engineering materials

Engineering Student
Chapter 5:INTAKES

Content
• Definition
• Site Selection of an intake
• Classification of Intake
• Characteristics of Intake

Intake
The basic function of intake structure is to help in safely withdrawing water from
the source and then to discharge this water in to the withdrawal conduit, through
which it reaches the water treatment plant.
It is constructed at the entrance of the withdrawal pipe and thereby protecting it
from being clogged by debris.
Some times from reservoirs where gravity flow is possible, water is directly
transmitted to the treatment through intake structure.
 Intake generally consists of:
 An intake conduit with screen at its inlet end anda valve to control the flow of water
 A structure permitting the withdrawl of water from the source and housing and supporting
the intake conduit, valve operating devices, pumps etc.

Site Selection of anIntake
 Located in a pure water zone with availability of water
 As far as possible, it should be near the treatment plant to minimize conveyance cost.
 Far from disposal points of waster water
 Should never be located near or in the navigation channel (river traffic)
 It should be in deep water to ensure water supply even under worst conditions
 Site should have sufficient scope for future extensions if needed be.
 It should be accessible even during flood and should not be flooded
 Should not be located on curves
 Site should be free from river attack (scouring, silting, storms, water current effects)
 Site should have good foundation conditions

Classification of Intakes
INTAKES
Submerged intakes
Exposed intakes
WetIntake
Dry Intake
River Intake
Reservoir Intake
Spring Intake

SubmergedIntake
 These intakes are constructed entirely inside
the water.
 Simple concrete block supporting thestarting
end of the withdrawal pipe.
 Covered by screen to prevent the entry of
debris etc.
 Chances of siltation: Elevated 2 to 2.5m above
the lake bed level to avoid entry of silt.
 They are cheap & do not obstruct navigation
 Widely used for small water supply projects
drawing water from streams or lakes having a
little change in water level through out year.
 Limitation: Not easily accessible for cleaning &
repairing.
 Example: concrete block, rock filled

ExposedIntakes
Exposed intakes are mainly in the
form of tower or well constructed
near the bank of river, or
sometimes away from the river
banks.
There are very common due to
the ease of operation

Wet Intake
e
as
 Here, the water level is practically the same as th
water level of the sources of supply.
 Also known as jack well or sump well.
 It consist of a concrete circular shell filled with
water up to the reservoir level and has a vertical
inside shaft which is connected to the withdrawal
pipe.
 The withdrawal pipe may lie over the bed of the
rivers or may be in the form of tunnels below the
riverbed.
 Openings are made into the outer concrete shell
well as, into the inside shaft.
 Gates are usually placed on the shaft, so as to
control the flow of water into the shaft and the
withdrawal conduit.
 The water coming out of the withdrawal pipe may
be taken to pump house for lift

Dry Intake
 The water is directly drawn into the withdrawal
conduit through the gated entry ports.
 It has no water inside the tower if its gates are
closed.
 When the entry ports are closed, a dry intake
tower will be subjected to additional buoyant
forces.
 Hence it must be of heavier construction than wet
intake tower.
 They are useful since water can be withdrawn from
any selected level of the reservoir by opening the
port gate levels.

RiverIntake
It consists of masonry or RCC structure intake
tower.
Provided with several inlets called penstocks for
withdrawing water from the river.
Penstocks are located at different level to permit
with-drawl even when water level drops.
The inlet end is provided with screen to prevent
entry of floating debris.
Also provided with valves to control the entry of
water through penstocks.
 These valves are operated from the control room
at the top.
In this case the intake is filled with water and we
call it as wet intake tower.
For maintenance and cleanliness, ladder is usually
provided in the intake tower.

RiverIntakes
of
d
y,
It may either be located sufficiently inside the river so that
demands of water are met with in all the seasons of the year, or
they may be located near the riverbank where a sufficient depth
water is available.
Sometimes, an approach channel is constructed and water is lea
from upstream to the intake.
The requirement of pumping from intake depends on topograph
but preferably gravity system.
If the river has wide basin, then a cross approach channel may be
constructed up to the intake to fetch the water from deeper
portion of river.
If the water level in the river varies with season, a weir or barrage
may be constructed across it to raise the water level and divert it
to the intake tower.
When riverbed is soft or unstable, the intake is founded slightly
away from the bed.
It is submerged under the lowest water level of river.

Ranijamara Irrigation Project (Side Channel Intake)

ReservoirIntake
It depends on the type of dam constructed to create the reservoir:
 Earthen Dam
 GravityDams

EarthenDam:
 The intake tower is connected to the top of the dam by a foot bridge
 The water from the reservoir is withdrawn by intake pipes are at different levels with the
common vertical pipe.
 The vertical pipe is connected to the bottom to an intake conduit which is taken out through
the body of the dam.
 Each intake pipe is provided with a bell-mouth inlet that has the fine screen to permit entry of
clear water.
 Pipes at different level maintain level of reservoir.
 Intake pipes are provided with valves to control the flow of water.
 The control room is at the top to operate valves.
 Common vertical pipe enters the conduit which carries water to the treatment plant.
 The dry intake tower has pipes fitted inside.

GravityDam
 In case of gravity Dam , two alternative forms of intakes can be built.
First case: entry of water is through a single port which has trash rack structure to
check the entry of debris and other floating materials.
Second case: intake well is provided in the main body of dam. Water enters the
well through inlet ports provided at various levels to enable the with drawl of
water even when the water level drops. Inlets are provided with screens.
Water is withdrawn through outlets or sluice gate which are provided as an
integral part of dam.
 Gates and valves are provided to control the flow of water through the outlets.

Babai Irrigation Project Headworks

Sikta Irrigation Project Headworks

Spring Intake
A spring intake is provided to abstract
water from a spring source.
It also prevents outside water and other
sources of pollutants from entering into
the water supply system.
The intake thus protects the water from
getting contaminated.
The water outlet point of spring should be
properly identified before the construction
of intake.
Low yield sources should not be tapped for
gravity flow scheme.
Selection criteria:
The place should be close to the source as
possible.
The place should be above populated or farming
areas.
The place should be above foot path, cattle
watering and washing places.
Places where surface water run-off during the
monsoon can be easily drained off.
Where the immediate surrounding above the
spring is not easily accessible to people and
livestock.
Where general condition of terrain does not
allow water logging.

It consists of two chambers
 collection chamber
 valvechamber.
Collection chamber
It should be awayfrom the source as far as possible.
The base of the collection chamber is made of plain cement concrete to avoid leakage.
All walls are made of stone masonry.
The heavy structure is avoided to avoid its settlement.
In order to reduce the backup pressure, the collection chamber needs to be
constructed awayfrom the source.
The collection chamber is provided with the wing walls on both sides which divertthe
water from the source to the collection chamber.
The collection chamber acts as sedimentation tank, which removes suspended
particles and turbidity.
In monsoon, the turbidity of the water is high, so special treatment with sedimentation
and filters are needed.
As far as possible the treatment work should be avoided to reduce the cost so a pure
source needs to be selected

The gravel and packing are done in the water-bearing
layer upstream to prevent the coarse material entering
the collection chamber.
Water-bearing layer is covered with the plastic sheet
and clayfilling.
The outlet pipe fitted with screens is kept at about 10 to
15 cm above the floor to screen out the suspended
particles to enter into the transmission main of water
supply system.
The water contains particle in it which may settle down
in the collection chamber as sediments which should be
washed out when it reaches 5 cm of the outlet pipe.
The washout pipe is carried down the slope to allow the
sediments to flow into the nearby drainage system.
The overflow pipe is provided in the collection chamber
to prevent the backup pressure.
The washout valve is operated when washing of the
sediments is done in the collection chamber.
Mild steel, concrete or stone masonry covers are used
to cover the collection and the valve chamber.

In the valve chamber
The valves are connected to outlet
pipe and washout pipe.
During normal operation outlet valve is
opened while washout valves are
closed but during washing of the
sediments from the collection is done it
is opened.
The vent pipe is provided to outlet
pipe to release air pressure.
The unions are provided to facilitate
the removal of valves during
maintenance works.

Protection of springintakes
Why do we need to protect spring intake?
 For safe drinking water free of contamination.
 For increasing quality and quantity of water content.
 For prevention of scarcity of water in near future.
Elements for protectionof spring intake:
 Afforestation
 Surface water drain
 Plantation (bush)
 Barbed wire fence
 Concrete covers.
 Retaining walls

Afforestation: Tress are planted above the spring sources
allow the water to seep rather than as surface runoff and
increaseintakewater.
Surface waterdrain:Surfacewaterdrainshouldbe 8m
above and around the spring to drain the surface water
run off during monsoon. The ditch should be deep, and
canbe linedwithdry stonemasonry.
Plantation(Bush): Plantationofgrassesbelowthe barbed
wire fencewhichalsoallowthewatertoseep.Grasses
and bushes preventthesurfacesoil erosion.
Barbedwire fence: Thereshouldbeno habitantandeasy
accesstoanimalsaroundspringsuptoa distanceof30 m
to 90 m to avoidcontamination.Topreventtrespassingof
humansand grazing animalsandcontaminationofspring
water, barbed wire fencingatadistanceof5m from spring
intake.
ConcreteCovers: Thecatchmentofa springsourcecanbe
roofedover withconcreteslabandburiedforfurther
protection.
Retainingwalls:Iferosionisseento be a majorproblem
then retainingwallsofgabionordry stone masonry are
builttostabilizelandaroundtheintake.

Engineering Students
Chapter6: WaterTreatment

Content
• Objective
• Treatment process and impurity removal
• Screening
• Plain sedimentation
• Sedimentation withcoagulation
• Filtration
• Disinfection
• Softening
• Miscellaneous Treatment
2

Introduction
It is the process of making the water suitable for the intended purpose
by removing the impurities present in it.
The quality of water should be analyzed prior to the treatment to know
its characteristics for the selection of correct treatment process.
The quality of treated water should be confirmed to the drinking water
quality standards.
Treatment does not completely remove impurities to zero but to a level
which will not harm human health as per the standard.
3

Introduction
Desired outcomes for drinking water treatment process:
Palatable: no unpleasant taste
Safe: free from pathogens
Clear: low turbidity
Aesthetically pleasant: Colourless and odourless
Reasonably soft
Non-corrosive
Low organic content
4

Objectives of WaterTreatment
Toremove colour, dissolved gases and murkiness of water
Toremove objectionable taste and odour
Toremove pathogens; disease causing micro-organisms
Toremove hardness of water
Tomake water suitable for a wide variety of industrial
purposes such as brewing, dyeing etc.
5

Treatment Process and ImpurityRemoval
Screening
Plain sedimentation
Sedimentation aided with coagulation
Filtration
Disinfection
Softening
Miscellaneous Treatment:
Aeration,removal of iron, manganese etc.
6

Screening
Removes large floating matters such as sticks,
polythene bags, branches, leaves etc.
Screens are generally provided in front of the
pumps or intake works to exclude these large
debris
They serve as a protective device for the rest
of the treatment plant/process.
 Types:
 Coarse screen
 Fine screen
9

Plain Sedimentation
 Sedimentation removes suspended particles that are heavier than water by gravitational
settling.
 Plain sedimentation is the process in which water is retained in a tank or basin so that the
suspended particles present in water may settle under the action of gravity without the
addition of any chemical
 Suitable for water containing a large number of suspended solids of relatively large size.
 Plain sedimentation removes coarse and heavy suspended particles of specific gravity 1.2
and above.
 This process effectively removes suspended particles' color, odor, taste, and turbidity.
 The time when water is retained in a sedimentation tank is known as the detention or
retention period.
 The particles settled at the bed of the sedimentation tank are known as sludge.
11

Theory ofsedimentation
Velocity of flow of water
Viscosity of water
Size and shape of particles
Specific gravity of particles
Surface Overflow rate
Detention period
Inlet and outlet arrangements
Effective depth of settling zone
12

SedimentationTank
1. Quiescent Type Tank
2. Continuous Type Tank
1. Horizontal FlowTank
2. Vertical Flow Tank
17

Horizontal flowtank
Assumptions:
A particle is said to be removed if it reaches the bottom of the settling
sludge zone in the sedimentation tank.
Concentration of particles at every point in the vertical cross section of
sedimentation tank is assumed to be same as that of the inlet end.
The particle will settle in the settling zone exactly in the same manner
as in a quiescent condition of equal depth without any disturbance.
Flow of water is steady and velocity is uniform in all parts of the settling
zone for a time equal to the detention period.
18

Designcriteria
Assumption:
Time taken by water to move from one end to the other end should be equal or
greater than the time taken for the settling of particles.
𝐿
≥
𝐻
𝑉𝐻 𝑉𝑆
𝐿
≥
𝐻
𝑄/𝐵𝐻 𝑉𝑆
𝐿𝐵𝐻
≥
𝐻
𝑄 𝑉𝑆
𝑆
𝑉 ≥
𝑄
𝐵𝐿
 Efficiency of sedimentation tank;
𝑉𝑜
𝜂= 𝑉𝑆
*100
19

Circular sedimentationtank
• Circular basins are often referred to as clarifiers.
• These basins share some of the performance advantages of the
rectangular basins, but are generally more prone to short circuiting
and particle removal problems.
• Volume of circular tank
V= 𝐷2(0.785𝐻 + 0.011𝐷)
25

Vertical SedimentationTank
 These tanks are square or circular in shape at the
top.
 The shape of the base of this tank is hopper type.
 This are vertical flow tanks, because water flows
upward & downward in these tank.
 The water enters in this tank from top centrally
placed inlet channel.
 Because of deflector box water flows from upper
to lower.
 The sludge is collected at the bottom of the tank
where it is removed by a sludge pipe connected to
a pump.
 The clear water flows out through a
circumferential weir discharging into a draw off
channel.
26

Steps for designing a SedimentationTank
Step 1: discharge (Q), velocity (V)are given
then you calculate surface area A= Q/V
Step 2: L/B =3 to 5
surface area (A)=L*B
so calculate L and B
Step 3: Volume= Q* detention time (4-8 hours)
L*B*H= volume, so you get H
Step 4: Add freeboard to get the height of tank
𝐻1 = 𝐻 + 𝐹𝑟𝑒𝑒𝑏𝑜𝑎𝑟𝑑 ; freeboard can be 0.3 to 0.5m
Step 5: Check for SOR or vh
27

Numerical
A rectangular sedimentation tank for a town is treating water at a rate
of 18MLD with detention period of 4 Hrs.
a) Calculate the volume of water required.
b) If the allowable surface overflow rate is 500 l/hr/m^2 and ratio of L
to B, calculate the length and width of tank.
40

Numerical
Design a rectangular sedimentation tank for a town to purify the water
at a rate of 8*10^6 litres per day. Assume the velocity of flow as
15cm/minute and detention period as 5 Hrs.
41

Numerical
Design a circular sedimentation tank for a town to purify the water for the
following data.
Volume of water to be treated=3 million litres per day
Detention period=4 hours
Velocity of flow= 10 cm/min
Assume necessary data as applicable.
42

Sedimentation aided withcoagulation
Very fine suspended mud particles and colloidal matter present in water
cannot settle down in plain sedimentation tank of ordinary detention
period.
However, they can be removed easily by increasing their sizeby
changing them into flocculated particles by adding certain chemicals
(coagulants).
When coagulants are added to water upon through mixing forms a
gelatinous precipitate called “floc.”
The very fine materials get attracted and absorbed in these flocs
forming a bigger sized flocculated particles.
The coagulated water is finally made to pass through the sedimentation
tank where flocculated particles settle down and are thus removed.
Three operations are involved for this process:
 Feeding andmixing
 Flocculation
 Sedimentation
Coagulants:
1. Aluminumsulphate
2. Ferrous Sulphate
3. Ferric sulphate
4. Ferric chloride
5. Lime
43

HydrogenCopperas:
 Chemical formula:FeSO4.7H2O
 Acts whenpH is greaterthanor equalto8.5.
 Additionoflimegivesbetterresult.
 Limit:14mg/l
 It is cheaper comparedtoalum.
FeSO4.7H2O+Ca(OH)2= CaSO4+Fe(OH)2+7H2O
 Whencopperasisadded;
FeSO4.7H2O+Ca(HCO3)2=CaSO4+Fe(HCO3)2+7H2O
FeSO4.7H2O+2Ca(OH)2= 2CaCO3+Fe(OH)2+2H2O
 Finally;
Fe(OH)2+O2+H2O=Fe(OH)3 (precipitates)
Chlorinated Copperas
FeSO4.7H2O+ Cl2 = Fe(SO4)3+FeCl3
Fe2(SO4)3+Ca(HCO3)2=Fe(OH)3+CaSO4+CO2
• Colour is removed.
• Works in large pH range.
Lime:
 Waterhavinghigherconcentrationofphosphorousorammonia
 Phrangeis greaterthan 9.5
Sodium aluminate:
 Any hardness of calcium and manganese is reacted with sodium
aluminate and will form calcium aluminate and sodium will form
all the compoundsrespectivetohardness.
 It is very expensive.
 It canremovebothtemporaryandpermanenthardness.
 It no alkalinityisrequired.
 pH range= 6.6 to 8.5
 Can be usedinboiler wherethey wantno hardness.
Alum:
 Mostwidelyusedchemicalforcoagulationof water.
 It requiresalkalinityinwateranddoesnot work inacidicpH.
 Incasewaterisnot alkalinethenweaddlimetoprovide
alkalinity.
 Alum+Bicarbonate=floc+calciumsulphate(permanent
hardness)+carbondioxide(corrosion)+ water
44

Filtration
Filtration is the process of passing water through a thick
layers of porous media which in most cases is a layer of
sand supported on a bed ofgravel.
Filtration may help in removing colour, odour, turbidity
and some pathogenic bacteria from water.
 Theory of filtration:
Mechanicalstraining
 Sedimentation and adsorption
 Biological mechanism
 Electrolytic changes
Types offilter:
 Gravity filter
 Slow Sand filter
 Rapid Sand filter
Pressure filter
53

Theory offiltration
Mechanical straining:
The suspender which are of bigger sized
particles present in the water and which
are bigger then the size of the voids in the
sand layers of the filter, cannot pass
through these voids and get arrested in
them. The resultant water will therefore
be free from the impurities of larger sizes.
Most of the particles are removed in the
upper sand layers. The arrested particles
including the coagulant forms a mat on
the top of the bed, which further helps in
the straining out the impurities.
Flocculation and sedimentation:
It has been found that the filters are
able to remove even particles of size
smaller than the size of voids present in
the filter. This fact may be explained by
assuming that the void spaces act like
coagulation sedimentation tanks. The
colloidal matter arrested in the voids is
a gelatinous mass and therefore attract
other finer particles.
These finer particles then settle down
in the voids and gets removed.
54

Biological mechanism
Certain microorganisms and bacteria are
generally present in the voids of the filters.
They may either reside initially as coatings
over the sand grains or they may be caught
during initial process of filtration.
Nevertheless, these organisms require
organic impurities as their food for
survival. These organisms therefore utilize
such organic impurities and convert them
into harmless compounds by the biological
metabolism.
The harmless so formed layer are called
dirty skin or schmutzdecke. This layer
further helps in absorbing and straining
out the impurities.
Electrolytic Changes
It is also explained by the theory of
ionization. According to this theory, a filter
helps in the purifying the water by changing
the chemical characteristics of water.
This may be explained by the fact that the
sand grains of the filter media and the
impurities in. water, carry electric charges
of opposite nature.
When these opposite charged particles and
the impurities comes in contact, they
neutralize each other, there by changing the
character of water and makes it pure.
After a certain interval, the electric charges
of sand particles get exhausted and have to
be restored by cleaning the filter.
55

Construction of slow sandfilter
1. Enclosuretank:
• It is an open watertight rectangular tank constructed of stone, brick or concrete.
• Depth of tank=2.5 to 4m
• Surface area = 50 to 100 m^2
• Bed slope: 1in 100 to 1 in 200 towards central drain
2. Filter Media
• It consists of sand layers: 90 – 110cm in depth
• Effective size of sand varies from 0.25 to 0.35mm
• Uniformity coefficient varies from 3 to 5
• The top 15com of this sand bed is kept finer than the rest of the layers.
• Sand should not contain more than 2% of calcium and manganese as carbonates.
57

3. Base material
 Gravel is used as the base material which supports the sand layer.
 Thickness of gravel bed=30 to 75 cm
 The gravel bed is graded and it is laid in layers each of 15to 20 cm thickness.
 The top layer should be of small size gravel and bottom should be bigger size gravel.
4. Under drainage system
 The under-drainage system collects the filtered water and delivers it to the clean
water reservoir.
 It consists of central drain and lateral drains.
 The lateral drains are provided at a distance of 2-3m and they are stopped at a
distance of 50 to 80 cm from the wall of tanks.
 These drains are laid at certain angle and finally connected to central drain.
58

5. Inlet and Outlet arrangement
 For efficient working of slow sand filters various appurtenances are installed
on both inlet and outlet side:
 Vertical air pipe through sand layers
 Devices to control depth of water above filter media
 Devices for measuring loss of head through the filter media
 Devices for maintaining constant rate of flow through the filter
59

Working of slow sandfilter
Water from plain sedimentation tank is allowed to enter the filterthrough
inlet chamber.
The depth of water over the filter media is maintained generally equal to
the thickness of sand layer.
The water passes through the filter media and during this water gets
purified.
The purified wateris collected in the lateraldrains which are passed to
central drain and finally into clean water storage.
Slow sand filterare operated up to a maximum filter head of 75cm or 65 to
85% of the thickness of sand bed.
The loss of head calledfilter head is generallylimited to a maximum of 0.7
to 1.2 m.
After that limit, the filterunit must be out of service and filter must be
cleaned.
60

Cleaning of slow sandfilter
 The cleaning of slow sand filter is not done by backwashing as is done for rapid sand filter.
 Its is done by scrapping the top 1.5 to 3cm of sand layer.
The scrapped sand is either removed manually for washing or it is placed in a portable
hydraulic ejector which forces it through a hose to a washer outside filter bed.
 The top surface is finally raked, roughened, cleaned and washed with good water.
 The amount of water required is generally small (0.2 to 0.6% of the total water filtered)
 It requires cleaning every 1-3 months depending upon the impurities present in raw water.
The first water for 12 to 15 hours , we will not use for consumption but will let for the
formation of biological film around the sand grains. Only after that the filtered water will be
collected.
61

Water supply Engineering Notes by Sudip Khadka.pdf

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