2 MARKS QUESTIONS AND ANSWERS
1. What are the methods are available for population forecast?
i. Arithmetical increase
ii. Geometrical increase
iii. Incremental increase method
iv. Decreased rate of growth method
v. Graphical comparison method
vi. Growth composition analysis
vii. Ratio and correlation method
viii. Zoning method or master plan method.
ix. Graphical extension method
2. What are the factors affecting population growth?
1. Ecnonomic factors: Such as development of new industries, discovery of oil or other
minerals in the vicinity of the city.
2. Development programmes: Development of projects of natural importance, such as
river valley projects.
3. Social facilities: Educational, medical, recreational and other social facilities.
4. Communication links: Connection of the town with other big cities ,and also to
mantles of agricultural products.
3. Note about common impurities in water.
(i) Suspended impurities
(ii)Dissolved impurities
(iii) Colloidal impurities
4. What natural source of water?
(i) Pure water
(ii) Rain water
(iii) Surface water
(iv) River wate.
5. What are the formulae available for find out fire demand?
1.kuichling’s formula
Q= 3182 P
Q= quantity of water in lit/min
P= population in thousands.
2. buston’formula
Q= 5663 P
3. Freeman’s formula
P
Q= 1136(  10 )
5
F= 2.8 P
F= number of simultaneous fire streams
6. Compute the ‘fire demand’ for a city having population of 1,40,000 using formula
Solution:
P=population in thousands = 140
1. kuichling’s formula
Q= 3182 P
=3182 140 =37650 lit/min.=0.627 cumes
2. Buston’ formula
Q= 5663 140 =67000 lit/min= 1.117 cumes
3. Freeman’s formula
P
140
 10 )=1136(
 10 )=43168 lit/min=0.719 cumes.
5
5
7. What are purposes of water analysis?
Q= 1136(
i) To classify the water with respect of general level of mineral constituents.
ii) To determine the degree of clarity and ascertain the nature of matter in suspension
iii) To determine the chemical and bacteriological pollution of water.
8. What are effects of impoundment on water quality?
Benefits
1.turbidity reduction
2.hardness reduction
3.organic oxidation
4. B.O.D reduction
5. colour reduction
6.cloriform reduction
Detriments
1.less mixing and less re-aeration
2. Algal blooms: bad taste and odour.
3. back up of pollutants
4. Thermal stratification.
i) low dissolved oxygen
ii) Iron and manganese dissolution
9. Write about common methods of measuring turbidity?
(i)By Turbidity rod
(ii) By Jackson’s turbidimeter.
(iii) By Baylis turbidimeter.
(iv)By Nephelometers.
10. Define: pH
It defined as, logarithmic of reciprocal of hydrogen ion concentration
1
pH= - log10(H) = log10(
)
H
11. Write about most probable number (MPN)
The most probable number (MPN) of coliform or E-coli is defined as that bacterial
density ,which if it had been actually present in the sample under examination ,would more
frequently present in the sample under examination ,would more frequently than any other ,have
given the observed analytical result.
12. Write about agar plate count test.
This test carried out to find the number of bacteria colonies growing on a specified
medium incubated for a specified temperature .The enumeration of the total bacteria is therefore
known as colony count.
13. Write note on sulphur bacteria.
Sulphur bacteria are autotrophic bacteria which oxidize elemental sulphur or reduced
sulphur compounds, obtaining their carbon requirements from carbon dioxide .they are
undesirable in water used in many industrial.
Process and the acid produced during their metabolism may be destructive to concrete
and other structures .there is also the group of anaerobic bacteria, known as sulphate reducing
bacteria which reduce sulphate to hydrogen.
14. What are the water –borne bacterial diseases?
i) Typhoid fever
ii) Paratyphoid fever
iii) Cholera
iv) Bacillary dysentery
15. What are the purposes of pumping?
i) To lift the raw water from the source of supply,such as lake ,reservoir ,river or well.
ii) To lift the treated water to overhead tanks or reservoir.
iii) To boost the line pressure
iv) To supply water under pressure for fire hydrants.
16. What are the types of well pumps?
i) Hand pumps
ii) Reciprocating pumps.
iii) Centrifugal pumps
iv) Air lifts pumps.
v) Jet pumps.
17. What are the typical installations required for centrifugal pumps?
i) Strainer
ii)Foot valve
iii) Suction pipe
iv) Accentric reducer
v) Centrifugal pump
vi)Expander
vii)Check valve
viii)Gate valve
18. What are the advantages of C.I pipes?
1) C.I pipes are of moderate cost
2) Their jointing is easier
3) They are resistant to corrosion
4) They have long life.
19. What are stresses in pipes?
i) Internal water pressure
ii) External pressures due to overburden etc.
iii) Temperature stresses
iv) Water hammer
20. Write about pipe appurtenances?
i. Sluice valve or gate valve
ii. Air relief valves
iii. Reflux valves
iv. Pressure relief valves
v. Scour valves
16 MARK QUESTIONS AND ANSWERS
1. Explain the displacement pumps?
The displacement pumps are two types
1. Reciprocating pumps
2. Rotary pumps
Reciprocating pumps
This is the most common type of the displacement pumps. It essentially consists of piston
or a plunger which moves to and fro close fitting cylinder which is connected to the suction and
delivery pipes .The suction and delivery pipes are provided with non-return or one way valve
which admits water in one direction only.
During the suction stroke, when piston or plunger moves outwards, a partial vacuum is
created in the cylinder, which enables the atmosphere pressure acting on the liquid surface in the
sump below to force the liquid up the suction pipe and fill the cylinder by forcing open the
suction valve. The cycle of suction stokes and delivery stokes s then repeated .The piston or
plunger is moved by a crank rotated at uniform speed by a driving engine or motor.
It has two suction and two delivery pipes with appropriate valves .During such stroke,
suction takes on one side of the piston while the other side delivers the liquid. Due to this, there
are two suction strokes and two delivery strokes in one revolution of the crank.
In a double cylinder or two cylinder two throw pumps, two single acting cylinders are
provided, and each cylinder has separate suction and delivery pipes with appropriate valves. The
plunger of the two cylinders is operated by cranks set at 1800. In the case of three cylinder pump
or three throw pump, each single has its own suction and delivery with apporatite valves, with
their cranks set at 1200. A duplex double action pump is equivalent to a four throw pump, and is
formed by combining two-double cylinder pumps.
Rotary pumps.
In rotary pumps, two gears or cams mesh together and rotate in opposite directions. The
rotating elements fit closely in the casing, so that water is drawn up the suction pipe, trapped
between the teeth or cams and the casting and forced out into the discharge. In the rotary pump,
no valves are requires and flow is practically displacement are: gear, lobe, screw and vane
pumps.
2. Compare the reciprocating pumps and centrifugal pumps.
Characteristics
1.discharge
Reciprocating
i)Flow pulsating
ii)Constant discharge even
if head on delivery side
varies
Centrifugal pumps
i)continuous flow
ii) Does not give constant
discharge under variable
head.
2.speed
3. efficiency
4. head
5.size
6. initial and maintenance
cost
7.runing
Run at low speeds: piston
speed less than 30 m/min.
If coupled to driving
machines, speed reducing
devices necessary.
Long stroke engines have
85% efficiency while
smaller pumps have only
40% efficiency.
Can work against high
heads,
Large size, bulky and
heavy. It requires large
space.
High initial cost: maintain
cost is also high.
Starting is difficult :more
power required:
complicated mechanism
required
Run at high speed (500 to
1000r.p.m).direct
connection with driving
machines possible.
Efficiency between 40 and
80 %: more efficiency if
the head and discharge are
maintained within narrow
limits.
Better suited to low heads.
Small, compact and light.
Low initial cost.
Maintenance cost low.
Starting is easy; less power
required: simple
mechanism; operation
easier.
3. Explain in briefly methods used for prediction of future population of a city, with
reference to the design of a water supply system.
Arithmetical increase
This is the simplest method of population forecast, though it generally gives lower
results. In this method, the increase in population from decade is assumed constant
.Mathematically; this hypothesis may be expressed as
dP
=K
dt
dP
is the rate of change of population and K is a constant. From the census data of
dt
past 3 or 4 decades, the increases in population for each decade is found, and from that an
average increment is found. For each successive, future decade, this average increment is
added .the future population Pn after n decade is then given by
Where,
Pn= P + nl
Where, Pn = future population at the end of n decades
P = present population
I = average increment for a decade.
Geometrical increase
In this method, it is assumed that the percentage increase in population from decade to
decade is constant .from the population data of previous three or four decades, the percentage
increase in population is found and its average is found .if Ig is the average percentage
increase per decade, or rg is the increase per decade expressed as ratio, the population Pn
after n decades is given by
Pn= P(1+
Ig
)= P(1 + rg)n
100
Incremental increase method
This method combines both the arithmetic average method and the geometrical average
method. From the census data for the past several decades, the actual increase in each decade
is first found. Then the increment in increase for each decade is found. From these,an average
increment of the increases (known as incremental increase ) is found .the population in next
decade is found by adding to the present population the average increase plus the average
incremental increases per decade , and so on. Thus the future population at the end of n
decades is given by:
Pn= P+nL+
n(n  1)
r
2
Where P= present population
I= average increase per decade
r= average incremental increase
n= number of decades
Decreased rate of growth method
It is found that the rate of increase of population never remains constant, but varies.
Figure shows a plot between the population P and the time T for a developing city .the
population of a city will grow until it reaches a saturation population which is established by
limit of economic opportunity. All population thus grow according to the logistic or S-curve .the
curve ABC starts with a lower rate of growth, followed by a high rate and then at a progressively
lower rate to the saturation population. Thus in figure part AB has geometric increase while there
is the first order increase from B 20 C. From D to E, near point of inflection, there is straight line
increase .the curve abc is the first derivative curve indicating the rate of the growth.
It is seen that in the part be of the curve, the rate of increase decrease .From figure ,it
shows the sane pl0ot in which the population is plotted on log scale. It is clear that for part
A1B1.we have increasing rate of the growth while for the part B 1C1, there is decreasing rate of
the growth of population
Graphical extension method
In this method, a curve is drawn between the population P and time T, with the help
of census data of previous few decades, so that the shape of the population curve is obtained
–up to the present period .the curve is the n carefully extended from the present to the future
decades .from the extended part of the curve, the population at that end of any future decade
is approximately determined.
Graphical comparison method
This method is a curve variation of the previous method. It assumes that the city under
consideration will develop as similar cities developed in the past .the method consist of plotting
curves of cities that, one or more decades ago, had reached the present population of the city
under consideration.
From figure, population of city A under consideration is plotted up to 1970 at which its
population is 62,000. The city B having similar condition, reached the population of 62000 in
1030 and its curve is plotted from 1930 onwards. The curve of city A can be then be continued,
allowing it to be influence by the rate of growth of the larger cities .In practice however; it is
difficult to find identical cities with respect to population growth.
Zoning method or master plan method.
This is probably a scientific method using the limitations imposed by the town planner
in the increase in density of population of various parts of the city. For this, a master plan of the
city is prepared, dividing it into various such as industrial, commeriacl, residential and other
zones.
Each zone is allowed to develop as per master plan only. The future population of each
zone, when fully developed can be easily found. This method more advantages because of the
fact that the total water requirement of the city depends not only for domestic purposes, but also
for commercial, industrial, social health and other purposes.
Ratio and correlation method
The population growth of a small town or area is related to big towns or big areas. The
increases in population of big cities bear a direct relationship to the population of the whole state
or country. In this method, the local to national population ratio is determined in the previous
two to four decades.
Depending upon conditions or other factors, even changing ratio may be adopted. These
ratios may be used in predicating the future population .This method takes into account the
regional and national factors affecting population growth in the past is fairly consistent with that
of state or nation.
Growth composition analysis
The change in population of a city is due to three reasons:
(i)Birth(ii) death(iii) migration from villages or other towns. The population forecast may be
made by proper analysis of these three factors. The differences between birth rate and death rate
give the natural increase in the population .Thus,
Pn= P + natural increase + migration
4. Write a note on variations in rate of water demand.
Residential or domestic use
The residential or domestic use includes use includes water requirements for drinking, cooking,
bathing, washing of clothes, utensils and house and flushing of water closets . Provisions are
sometimes made for domestic animals .IS-1172-1957 recommends a per capita water
consumption of 135 liters per day.
Water requirements for domestic purposes
S.no
Description
Amount of water in liters per head per
day
1
Bathing
55
2
Washing of clothes
20
3
Flushing of W.C
30
4
Washing the house
10
5
Washing the utensils
10
6
Cooking
5
7
Drinking
5
Totals
135 liters
Public or civic use
Water required for public or civic uses may be for the following purposes
(i)
road washing
(ii)
sanitation
(iii)
public parks and
(iv)
Fire fighting.
For road washing in the municipality area, provision of 5 Litres per head per day is made
.similarly, for sanitary purposes .Such as cleaning public sanitary blocks, flushing sewer systems
etc., a provision of 3 to 5 liters per head per road mat be made .water required for maintaining
public parks etc. may be 2 to 3 liters per square meter per day.
Industrial use
The presence of industries in or near the city has great impact on the water demand .The
quantity of water required depends upon the type of industry. For city moderate factories, a
provision of 20 to 25 percent of the per capita consumption may base on nature and magnitude of
each industry and the potential for its expansion.
Water system
Losses from a water distribution system consists of (i) leakage and over-flow from
service reservoirs (ii) leakage and losses on consumers premises when they get un-metered house
hold supplies (iv) under-registration of supply meters and (v) large leakage or wastage from
public taps. Losses in the supply lines are mainly due to defective pipe joints, cracked pipes, and
loose valve sand fittings .in the case of well maintained and fully metered water distribution
system, the losses may hardly exceed 20% of the total consumption.
Institutional use
The manual on water supply and treatment recommends the values of water requirement for
institutional needs as given in table
Description
Amount of water(lpcd)
1.For communities with population up to
20,000
40
a) water supply thorough stand post
70 to 100
b) water supply thorough house
service connection
2. For communities with population 20,000
to 10,000
100 to 150
3.For communities with population above
100,000
150 to 200
5. Discuss various factors that affect rate of demand.
Size and type of community
The fluctuations in demand depends upon the size of the city .in large city, the
fluctuations in demand may be narrow .in a small city ,per capita water consumption is to be
expected to be small because there are only limited uses for water in a small town. The
fluctuation in use in an industrial community is normally much smaller than in a residential
community.
Standard of living
The higher the standard of living is, the higher the demand and greater the variation in
demand.
Climatic conditions
If the community is located in hot climate, water use will be increased by bathing .Lawn
sprinkling and use in parks and recreation fields. Similarly, in extreme cold climates, water may
be waste at the faucets to prevent freezing of pipes, resulting in increased consumption .extremes
of heat and cold cause variations in demand.
Quality
Poor- quality water results in increased use while low pressure results in decreased use.
Pressure in the supply
High pressure results in increased use while low pressure results in decreased use.
System of supply
Water supply may either be continuous or intermittent .Generally; intermittent supply will reduce
rate of demand.
Sewerage
Use of water increases when sewers are installed in an area previosoly without them.
Metering
Use of water decreases in water rates will reduce consumption in metered.
Water rates
An increase in water rates will reduce consumption in metered areas.
Age of community
Older, more stable communities use less water than rapidly developing communities
where new homes are being constructed and owners are planting new lawns.
6. Explain the Quality of water resource
Pure water
Chemically pure water is a combination of two elements: hydrogen and oxygen, with a
chemical symbol H2O and chemical nature gas as hydrogen monoxide .It is not possible to find
absolutely pure water in nature. Also, it is not economically feasible to manufacture pure water
in this form. However, pure water in this form.
Rain water
When precipitation take place ,the rain water ,falling through atmosphere absorbs various
gas and vapors which are normally present in the atmosphere .Thus , rain water absorbs oxygen
,nitrogen ,CO2 ,rare gas ,sweep particulates, salt nuclei, radio-active fallout.
Surface runoff
When the rain water falling on the ground surface takes from of surface runoff, it picks
up particulates (silt and clay), organic matter, nitrates, phosphates etc. The characteristic of the
surface runoff water thus depends upon the topography and vegetation of the catch -ment, along
with land use and management .Thus the surface runoff water contains.
River water
Since the surface runoff water normally joins the rivers and streams, the characteristics of
river water are practically the same as those of surface runoff water. However, if the river
receives the municipal and industrial wastewater, additional pollution parameters are added to it.
Lake and pond water
When water is ponded in lakes and reservoirs, algae and similar other organisms grow on the
surface, giving rise to odours, tastes and colors. Decaying vegetation further intensifying these
elements .In addition to this, thermal stratification takes place in reservoirs resulting
1) Low dissolved oxygen
2) Dissolution of iron and manganese
3) Production of H2S
4) Increase in CO2
5) Reduction in pH of water.
Ground water
When rain water infiltrates into the ground to join the water table, it becomes “ground water”
.Ground water has following characteristic
1) It absorbs gases of decomposition and degradable organic matter (such as
H2S, methane) within the pores of soil mantle through which it percolates.
2) In earth strata which in rich are organic matter, oxygen is removed from percolating
water and CO2 is added.
3) Ground water has lower pH value.
4) Soil minerals are dissolved in ground water. Carbonates, sulphates and chlorides are
added, resulting in hardness.
5) Ground water may contain iron and manganese’s in soluble form.
7. Explain the types of pipes
Cast iron pipe
Cast iron pipes are used in great majority of water in distribution mains because of
centuries of satisfactory experience with it. Cast –iron pipe is resistant to corrosion and
accordingly is long lived –its life may be over 100 years.
Cast iron pipes are manufactured by two methods (i) ordinary sand moulding process (ii)
centrifugal process. In sand casting, molten metal is poured into sand lined moulds that are set in
either a vertical or horizontal position. Horizontally cast pipes are referred to as pit Cast.
Mcwarne pipes are 100 percent stronger in tension and 50 per cent stronger in rupture than pit
cast pipes.
Advantages of C.I pipes
5) C.I pipes are of moderate cost
6) Their jointing is easier
7) They are resistant to corrosion
8) They have long life.
Dis -advantages
1) They are subject to tuberculation in certain waters, due to which their carrying capacity is
reduced to as much as 70%.
2) They are heavier and hence uneconomical when their diameter is more than 120 cm.
3) They can not be used for pressures greater than 7 Kg/cm2
4) They are fragile.
Wrought iron and galvanized iron pipes
Wrought iron pipes are manufactured by rolling flat plates of the such pipes are much
lighter than the C.I pipes and can be more easily cut ,threaded and worked .they look much
neater ,but are much costlier.
They corroded quickly, and hence are used principally for installation within buildings.
These pipes are usually protected by coating them with a thin film of molten zinc. Such coated
pipes are known as galvanized iron pipes, and they are commonly jointed by screwed and
socketed joints.
Steel pipes
Steel pipes of small diameter can be made from the solid, but the larger sizes are made by
riveting together the edges of suitably –curved plates, the sockets being formed later in a press.
The joints may be either transverse or longitudinal or transverse and spiral.
Hence they should be placed under favorable conditions in which high external pressures
are not expected to fall on the pipes .steel pipes particularly suitably on bridges or under similar
conditions where strength and low weight are desired. Most steel pipes are produced plain end
and are therefore connected with couplings.
Cement concrete pipes
Cement Concrete pipes may be either plain or reinforced and are best made by spinning
process. they may be either pre-cast, or may be prepared at the site .The plain cement concrete
pipes are used for heads up to 7 m while reinforced cement concrete pipes are normally used for
heads 60 m.
Advantages
1) They are more suitable to resist the external loads due to backfilling.
2) They maintenance cost is low
3) The inside surface of pipes can be made smooth, thus reducing the frictional losses.
4) The problem of corrosion is not there.
5) Pipes can be cast at site, and hence the transportation problems are reduced.
6) Due to their heavy weight, the problem of floatation is not there when they are empty.
Disadvantages
1) Un-reinforced pipes are liable to tensile cracks ,and they cannot with stand high
pressure
2) The tendency of leakage is not ruled out as a result of its porosity and shrinkage
cracks.
3) It is very difficult to repair them.
4) Pre-cast pipes are very heavy, and it is difficult to transport them.
Asbestos cement pipes
Asbestos cement pipes are manufactured from asbestos fiber and Portland cement
combined under pressure to form a dense homogenous structure having strong bond between
cement and the fiber. Such a pipe is claimed to be completely impervious to passage of water
through its walls.
Their tensile and compressive strengths used in a design are 200 and 600 kg/cm2
respectively. They are generally manufactured under proprietary names .these pipes are finished
with plain ends, the exterior of the barrel being manufactured to receive the coupling.The joist
used in then asbestos cement pipes are of simple type, consisting of a sleeve which fits over the
plain ends of the lengths, water –tightness being obtained by two rubber rings compressed
between the sleeve and the pipe barrels as in figure. The joint thus becomes flexible and
watertight.
Advantages
1) They have smooth internal surface, due to which the frictional losses are reduced.
2) They are light and can be easily transported.
3) They can be easily cut, fitted or jointed.
4) Service connections can be easily taken, sine they can be easily drilled and tapped
5) They are anti-corrosive.
Disadvantages
1) They are soft and brittle .they are very weak under impact loading due to moving traffic.
2) They are can not be laid in exposed places.
3) They are not durable.
4) They are costly.
8. Explain briefly about the Pipe appurtenances
Sluice valve or gate valve
These are also known as shut off valves or stop valves. They are extensively used in the
distribution system to shut off the supplies whenever desired .they are also helpful in dividing the
water mains into suitable sections.
The spacing of such valves may between 150 to 300 meters. They are also placed at street
corners or where two pipe lines intersect. they posses the advantage over most other types of
valves ,of combining relatively low cost and offering almost no resistance to flow of water when
the valve is wide open .
Air relief valves
The water flowing through the pipe lines always contain some air. This air tries to
accumulate at high points, and may interfere with flow .Air relief valves are therefore provided
at the summits along the water pipe, to provide an exit for such accumulated air.
Air valves are also required to discharge air when a main is being filled and to admit air
when it is being emptied .the admission of air on emptying the main is of great importance on
steel mains, which may flatten if the pressure falls below that of the atmosphere.
Reflux valves
Reflux valves are also known as check valves or non-return valves. It is automatic device
which allows water to flow water to flow in one direction only. They are placed in water pipes
which obtain water from the pump. When the pump is stopped, the water in the pipe line does
not rush back and damage the pump.
Pressure relief valves
These are also known as automatic cutoff valves or safety valves .they are located at
those points where pressure is likely to be maximum .when the line pressure increases above the
pre-set value, the valve operates automatically, and the pressure is reduced.
Altitude valves
They are mainly used on those lines which supply water to elevated tanks or stand pipes.
They close automatically when the tank is full and open when the pressure on the pump side is
less than that on the tank side of the valve.
Scour valves
Scour valves or blow off valves or washout valves are ordinary sluice valves that are
located either at eh dead ends or at lowest points in the mains. They are provided to blow-off or
remove the sand and silt deposited in the pipe line .They are operated manually.
9. What is the Requirement of water quality?
1. It should be colorless and sparkling clear. It must be free from solids in suspensions and must
not deposit sediment on standing.
2. It should be of good taste, free from odour.
3. It should be reasonably soft.
4. It should be plentiful and cheap.
5. It should be free from disease producing bacteria or organisms.
6. It should free from objectionable dissolved gases, such as sulphuratted hydrogen.
It should, however, have sufficient quantity of dissolved oxygen.
7.It should free from harmful salts.
8. It should free from objectionable minerals, such as iron, manganese, lead, arsenic and other
poisonous metals.
9. It should be free from radio-active substance such as radium, strontium etc.
10. It should be reasonably free from phenolic compounds, chlories, fluoride and iodine.
11. It should not lead to scale formation and should be non-corrosive.