Rainwater harvesting

1
A
PROJECT REPORT
ON
“Rain water harvesting”
Submitted in Partial Fulfillment for the Award of
Bachelor of Technology Degree
Of
Rajasthan Technical University, KOTA
Session- 2012-2013
From 04/02/12 to 04/03/13
Session: - 2012-2013
Submitted To: Submitted By
(LACTURAR) Deep chaudhary
DEPARTMENT OF CIVIL ENGG.Chittaranjan
Sunil kaswan
Ashishprajapat
VIVEKANANDA INSTITUTE OF TECHNOLOGY (EAST)
JAGATPURA, JAIPUR-302025
(RAJASTHAN)

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PREFACE
The main aim of our project was to put our knowledge into
practical use. This project has given us the experience to work in the
actual field and it also teaches us to overcome the practical situation
faced in real life and to interact with people, keeping ourselves calm
and patience in cases of difficulty.
This project report is a brief description about our work done
under the guidance of MR. NARAYAN MEGHNANIIt consists of the
various departments that we’ve visited and the various tasks that
we’ve done over there.
We would like to say that this project has helped to shape the
practical knowledge that as a person we have inside us and it would
also help me throughout our life and for this we are very thankful to
all the persons who helped us during our project period.
Thanking you

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ACKNOWLEDGEMENT
At the outset, we thank God almighty for making our endeavor a success. We also express our
gratitude to PROF. NarayanMeghnani(Head of the Department),Civil Engineering for providing us
with adequate facilities, ways and means by which we were able to complete this project.
We express our sincere gratitude to our project Guide MR. AnandMathur (H.O.D.), Civil
Engineering for his constant support and valuable suggestions without which the successful
completion of this project would not have been possible.
We express our immense pleasure and thanks to all the teachers and staff of the
Department of Civil Engineering, Last but not the least, we thank all others, and especially our
classmates and our family members who in one way or another helped in the successful completion of
this work.
ALL GROUP MEMBERS

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ABSTRACT
At the rate in which India population is increasing, it is said that India will surely replace China from
its number 1 position of most densely populated country of the world after 20-30. These will lead to
high rate of consumption of most valuable natural resource „Water‟ is resulting in augmentation of
pressures on the permitted freshwater resources. Ancient method of damming river and transporting
water to urban area has its own issues of eternal troubles of social and political. In order to conserve
and meet our daily demand of water requirement, we need to think for alternative cost effective and
relatively easier technological methods of conserving water. Rain water harvesting is one of the best
methods fulfilling those requirements. The technical aspects of this paper are rainwater harvesting
collected from rooftop which is considered to be catchment areas from all hostels and Institutes
departmental building at V.I.T. Campus. First of all, required data are collected i.e. catchment areas &
hydrological rainfall data. Water harvesting potential for the hostels and faculty apartments was
calculated, and the tank capacity with suitable design is being considered. Volume of tank has been
calculated with most appropriate method of estimation. Optimum location of tank on the basis of
hydrological analysis and GIS analysis was done in the campus. Finally, Gutter design, its analysis,
first flush and filtration mechanism are also dealt with in detail.
Keyword: Rainwater harvesting, first flush mechanism, Roof water system, Gutter for conveyance,
Underground RCC tank, Methods of distribution of harvested rainwater.

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CERTIFICATE
It is hereby certified that this is a bonfire record of the project report entitled “Rainwater
harvesting” has been completed by “DEEP CHAUDHARY, CHITTA RANJAN
MANDAL, SUNIL KASWAN, ASHISH PRAJAPAT” of the VIII semester, CIVIL
ENGINEERING in the year 2013 in partial fulfillment of the requirements to the award of
Degree of Bachelor of Technology in CIVIL ENGINEERING from VIVEKANANDA
INSTITUTE OF TECHNOLOGY(EAST) affiliated to Rajasthan Technical University,
Kota.
(H.O.D)
Mr. Anandlalmathur
DEPARTMENT OF CIVIL ENGINEERING

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CONTENTS
Page No.
Abstract - 4
Chapter - 1 Introduction 7-8
Chapter -2 Harvesting systems and its
features
9-10
Chapter -3 11
3.1. Studies Carried out Globally
3.2. Studies carried out in India
Chapter–4 12-16
Data collection
Chapter – 5
5.0. First flush system
Chapter – 6
17-27
28-29
6.1. Hydrological Analysis
6.2. Methods for storage of harvested
rainwater in tank
Chapter – 7
Types of tank and design
Chapter – 8
Detail and cost
Conclusion
31
37-40

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Chapter.1
Introduction
A sufficient, clean drinking water supply is essential to life. Millions of people throughout the world still do not
have access to this basic necessity. After decades of work by governments and organizations to bring potable
water to the poorer people of the world, the situation is still dire. The reasons are many and varied but
generally speaking, the poor of the world cannot afford the capital intensive and technically complex
traditional water supply systems which are widely promoted by governments and agencies throughout the
world. Rainwater harvesting (RWH) is an option that has been adopted in many areas of the world where
conventional water supply systems have failed to meet people’s needs. It is a technique that has been used
since antiquity. It is worth bearing in mind that rainwater harvesting is not the definitive answer to
household water problems. There is a complex set of inter-related circumstances that have to be
considered when choosing the appropriate water source. These include cost, climate, hydrology,
social and political elements, as well as technology, all play a role in the eventual choice of water
supply scheme that is adopted for a given situation. RWH is only one possible choice, but one that is
often overlooked by planners, engineers and builders.
The reason that RWH is rarely considered is often due to lack of information – both technical and
otherwise. In many areas where RWH has been introduced as part of a wider drinking water supply
programmed it was at first unpopular, simply because little was known about the technology by the
beneficiaries. In most of these cases, the technology has quickly gained popularity as the user
realizes the benefits of a clean, reliable water source at the home. the town supply is unreliable or
where local water sources dry up for a part of the year, but is also In many cases RWH has been
introduced as part of an integrated water supply system, where often used as the sole water source
for a community or household. It is a technology that is flexible and adaptable to a very wide variety of
conditions, being used in the richest and the poorest societies on our planet, and in the wettest and
the driest regions of the world.Storage tanks and cisterns
The water storage tank usually represents the biggest capital investment element of a domestic RWH system.
It therefore usually requires careful design – to provide optimal storage capacity while keeping the cost as low
as possible. The catchment area is usually the existing rooftop or occasionally a cleaned area of ground, as
seen in the courtyard collection systems in China, and guttering can often be obtained relatively cheaply, or
can be manufactured locally.
There are an almost unlimited number of options for storing water. Common vessels used for very small-scale
water storage in developing countries include such examples as plastic bowls and buckets, jerrycans, clay or
ceramic jars, cement jars, old oil drums, empty food containers, etc. For storing larger quantities of water the
system will usually require a tank or a cistern. For the purpose of this document we will classify the tank as an
above-ground storage vessel and the cistern as a below-ground storage vessel. These can vary in size from a
cubic meter or so (1000 liters) up to hundreds of cubic meters for large projects, but typically up to a maximum
of 20 or 30 cubic meters for a domestic system. The choice of system will depend on a number of technical and
economic considerations listed below.
1. Space availability
2. Options available locally
3. Local traditions for water storage
4. Cost – of purchasing new tank
5. Cost – of materials and labour for construction.

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One of the main choices will be whether to use a tank or a cistern. Both tanks and cisterns have their
advantages and disadvantages. Table 1 summarizes the pros and cons of each-:
Tank Cistern
Pros 1. Above ground structure
allows easy inspection
for leakages
2. Many existing designs to
choose from
3. Can be easily purchased
‘off-the-shelf’
4. Can be manufactured
from a wide variety of
materials
5. Easy to construct from
traditional materials
6. Water extraction can be
by gravity in many cases
7. Can be raised above
ground level to increase
water pressure
1. Generally cheaper due
to lower material
requirements
2. More difficult to empty
by leaving tap on
3. Require little or no
space above ground
4. Unobtrusive
5. Surrounding ground
gives support allowing
lower wall thickness and
thus lower costs
Cons
1.Require space
2.Generally more expensive
3.More easily damaged
4.Prone to attack from
weather
5.Failure can be dangerous
1.Water extraction is more
problematic – often requiring
a pump
2.Leaks are more difficult to
detect
3.Contamination of the
cistern from groundwater is
more common
4.Tree roots can damage
the structure
5.There is danger to children
and small animals if the
cistern is left uncovered

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Chapter.2
2.1.RAINWATER HARVESTING SYSTEMS AND ITS FEATURES -
Rainwater Harvesting is a simple technique of catching and holding rainwater where its falls. Either,
we can store it in tanks or we can use it to recharge groundwater depending upon the situation.
1.a. Features of Rainwater Harvesting are:
1. Reduces urban flooding.
2. Ease in constructing system in less time.
3. Economically cheaper in construction compared to other sources, i.e. dams, diversion, etc.
4. Rainwater harvesting is the ideal situation for those areas where there is inadequate
groundwater supply or surface resources.
5. Helps in utilizing the primary source of water and prevent the runoff from going into sewer or
storm drains, thereby reducing the load on treatment plants.
6. Recharging water into the aquifers which help in improving the quality of existing
groundwater through dilution.
2.2. COMPONENTS OF RAINWATER HARVESTING SYSTEM-
A rainwater harvesting system comprises of components for - transporting rainwater through pipes or
drains, filtration, and tanks for storage of harvested water. The common components of a rainwater
harvesting system are:-
1. Catchments: The surface which directly receives the rainfall and provides water to the system is
called catchment area. It can be a paved area like a terrace or courtyard of a building, or an unpaved
area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanized iron
or corrugated sheets can also be used for water harvesting.
2. Coarse Mesh: It prevents the passage of debris, provided in the roof.
3. Gutters: Channels which surrounds edge of a sloping roof to collect and transport rainwater to the
storage tank. Gutters can be semi-circular or rectangular and mostly made locally from plain
galvanized iron sheet. Gutters need to be supported so they do not sag or fall off when
loaded with water. The way in which gutters are fixed mainly depends on the construction of the
house, mostly iron or timber brackets are fixed into the walls. The detail of the designing part of the
Gutter is done in 7.3.
4. Conduits: Conduits are pipelines or drains that carry rainwater from the catchment or rooftop area
to the harvesting system. Commonly available conduits are made up of material like polyvinyl
chloride (PVC) or galvanized iron (GI).

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5. First-flushing: A first flush device is a valve which ensures flushing out of first spell of rain away
from the storage tank that carries a relatively larger amount of pollutants from the air and catchment
surface.
6. Filters: The filter is used to remove suspended pollutants from rainwater collected from rooftop
water. The Various types of filters generally used for commercial purpose are Charcoal water filter,
Sand filters, Horizontal roughing filter and slow sand filter.
7. Storage facility: There are various options available for the construction of these tanks with
respect to the shape, size, material of construction and the position of tank and they are:-
8. Shape: Cylindrical, square and rectangular.
9. Material of construction: Reinforced cement concrete (RCC), masonry, Ferro cement etc.
10. Position of tank: Depending on land space availability these tanks could be constructed
above ground, partly underground or fully underground. Some maintenance measures like
disinfection and cleaning are required to ensure the quality of water stored in the container.
If harvested water is decided to recharge the underground aquifer/reservoir, then some of the
structures mentioned below are used.
11. Recharge structures: Rainwater Harvested can also be used for charging the groundwater
aquifers through suitable structures like dugwells, borewells, recharge trenches and recharge pits.
Various recharge structures are possible some which promote the percolation of water through soil
strata at shallower depth (e.g., recharge trenches, permeable pavements) whereas others conduct water
to greater depths from where it joins the groundwater (e.g. recharge wells). At many locations,
existing structures like wells, pits and tanks can be modified as recharge structures, eliminating the
need to construct any fresh structures. Some of the few commonly used recharging methods are
recharging of dug wells and abandoned tube wells, Settlement tank, Recharging of service tube wells,
Recharge pits, Soak ways Percolation pit , Recharge troughs, Recharge trenches, Modified injection
well.

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Chapter.3
3.1. STUDIES CARRIED OUT GLOBALLY-
Today due to rising population &economical growth rate, demands for the surface water is
increasing exponentially. Rainwater harvesting is seems to be a perfect replacement for surface &
ground water as later is concerned with the rising cost as well as ecological problems. Thus,
rainwater harvesting is a cost effective and relatively lesser complex way of managing our limited
resources ensuring sustained long-term supply of water to the community. In order to fight with
the water scarcity, many countries started harvesting rain. Major players are Germany (Biggest
harvesting system in Germany is at Frankfurt Airport, collecting water from roofs of the new
terminal which has an large catchment area of 26,800 m2), Singapore (as average annual rainfall
of Singapore is 2400 mm, which is very high and best suited for rainwater harvesting
application), Tokyo (as RWH system reserves water which can be utilized for emergency water
demands for seismic disaster), etc.
3.2.STUDIES CARRIED OUT IN INDIA -
Today, only 2.5 per cent of the entire world’s water is fresh, which is fit for human consumption,
agriculture and industry. In several parts of the world, however, water is being used at a much
faster rate than can be refilled by rainfall. In 2025, the per capita water availability in India will
be reduced to 1500 cubic meters from 5000 in 1950. The United Nations warns that this shortage
of freshwater could be the most serious obstacle to producing enough food for a growing world
population, reducing poverty and protecting the environment. Hence the water scarcity is going to
be a critical problem if it is not treated now in its peanut stage.
Chapter.4

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DATA COLLECTION-
1. RAINFALL DATA COLLECTION –
Jaipur is located at westlongitude directionin Rajasthan.Jaipurhas a hot climate and not receives
high rainfall during Southwest monsoon (June-September) and retreating Northeast monsoon
(December-January). Average annual rainfall ranges between 50-80 cm.
TABLE NO.1: MONTHLY RAINFALL DATA OF ROURKELA STATION
Month Rainfall (mm)
January 10
February 24.9
March 0
April 0
May 0
June 10
July 20
August 15
September 20
October 0
November 0
December 15
TOTAL 114.9

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The case studies later in this document show a variety of tanks that have been built in different parts
of the world. In jaipur -
Collection surfaces
For domestic rainwater harvesting the most common surface for collection is the roof of the dwelling. Many
other surfaces can be, and are, used: courtyards, threshing areas, paved walking areas, plastic sheeting, trees,
etc. In some cases, as in Gibraltar, large rock surfaces are used to collect water which is then stored in large
tanks at the base of the rock slopes.
Most dwellings, however, have a roof. The style, construction and material of the roof affect its suitability as a
collection surface for water. Typical materials for roofing include corrugated iron sheet, asbestos sheet; tiles (a
wide variety is found), slate, and thatch (from a variety of organic materials). Most are suitable for collection of
roof water, but only certain types of grasses e.g. coconut and anahaw palm (Gould and Nissen Peterson, 1999),
thatched tightly, provide a surface adequate for high quality water collection. The rapid move towards the use
of corrugated iron sheets in many developing countries favors the promotion of RWH (despite the other
negative attributes of this material).
Guttering
Guttering is used to transport rainwater from the roof to the storage vessel. Guttering comes in a wide variety
of shapes and forms, ranging from the factory made PVC type to home made guttering using bamboo or folded

14
metal sheet. In fact, the lack of standards in guttering shape and size makes it difficult for designers to develop
standard solutions to, say, filtration and first flush devices. Guttering is usually fixed to the building just below
the roof and catches the water as it falls from the roof.
Figure 4: A typical corrugated iron sheet roof showing guttering
Some of the common types of guttering and fixings are shown in figure 5.

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Manufacture of low-cost gutters –
Factory made gutters are usually expensive and beyond the reach of the poor of
developing countries, if indeed available at all in the local marketplace. They are seldom
used for very low-cost systems. The alternative is usually to manufacture gutters from
materials that can be found cheaply in the locality. There are a number of techniques that
have been developed to help meet this demand; one such technique is described below.
V- shaped gutters from galvanized steel sheet can be made simply by cutting and folding
flat galvanized steel sheet. Such sheet is readily available in most market centers
(otherwise corrugated iron sheet can be beaten flat) and can be worked with tools that are
commonly found in a modestly equipped workshop. One simple technique is to clamp the
cut sheet between two lengths of straight timber and then to fold the sheet along the edge
of the wood. A strengthening edge can be added by folding the sheet through 90
o
and then
completing the edge with a hammer on a hard flat surface. The better the grade of steel
sheet that is used, the more durable and hard wearing the product. Fitting a downpipe to
V-shaped guttering can be problematic and the V-shaped guttering will often be continued
to the tank rather than changing to the customary circular pipe section downpipe. Methods
for fixing gutters are shown in figure 5.

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Chapter.5
First flush systems
Debris, dirt, dust and droppings will collect on the roof of a building or other collection area. When the first
rains arrive, this unwanted matter will be washed into the tank. This will cause contamination of the water and
the quality will be reduced. Many RWH systems therefore incorporate a system for diverting this ‘first flush’
water so that it does not enter the tank.
The simpler ideas are based on a manually operated arrangement whereby the inlet pipe is moved away from
the tank inlet and then replaced again once the initial first flush has been diverted. This method has obvious
drawbacks in that there has to be a person present who will remember to move the pipe.
Other systems use tipping gutters to achieve the same purpose. The most common system (as shown in Figure
7a) uses a bucket which accepts the first flush and the weight of this water off-balances a tipping gutter which
then diverts the water back into the tank.
The bucket then empties slowly through a small-bore pipe and automatically resets. The process will repeat
itself from time to time if the rain continues to fall, which can be a problem where water is really at a
premium. In this case a tap can be fitted to the bucket and will be operated manually. The quantity of water
that is flushed is dependent on the force required to lift the guttering. This can be adjusted to suit the needs of
the user.
Figure 7 – a) the tipping gutter first flush system and b) the floating ball first flush system.

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Another system that is used relies on a floating ball that forms a seal once sufficient water has been diverted
(see Figure 7b). The seal is usually made as the ball rises into the apex of an inverted cone. The ball seals the
top of the ‘waste’ water chamber and the diverted water is slowly released, as with the bucket system above,
through a small bore pipe. Again, the alternative is to use a tap. In some systems (notably one factory
manufactured system from Australia) the top receiving chamber is designed such that a vortex is formed and
any particles in the water are drawn down into the base of the vortex while only clean water passes into the
storage tank. The ‘waste’ water can be used for irrigating garden plants or other suitable application. The
debris has to be removed from the lower chamber occasionally.
Although the more sophisticated methods provide a much more elegant means of rejecting the first flush
water, practitioners often recommend that very simple, easily maintained systems be used, as these are more
likely to be repaired if failure occurs.
Filtration systems and settling tanks
Again, there are a wide variety of systems available for treating water before, during and after storage. The
level of sophistication also varies, from extremely high-tech to very rudimentary. A German company, WISY,
have developed an ingenious filter which fits into a vertical downpipe and acts as both filter and first-flush
system. The filter, shown in Figure 8, cleverly takes in water through a very fine (~0.20mm) mesh while
allowing silt and debris to continue down the pipe. The efficiency of the filter is over 90%. This filter is
commonly used in European systems.
The simple trash rack has been used in some systems but this type of filter has a number of associated
problems: firstly it only removes large debris; and secondly the rack can become clogged easily and requires
regular cleaning.
The sand-charcoal-stone filter is often used for filtering rainwater entering a tank. This type of filter is only
suitable, however, where the inflow is slow to moderate, and will soon overflow if the inflow exceeds the rate
at which the water can percolate through the sand. Settling tanks and partitions can be used to remove silt
and other suspended solids from the water. These are usually effective where used, but add significant
additional cost if elaborate techniques are used. Many systems found in the field rely simply on a piece of cloth
or fine mosquito mesh to act as the filter (and to prevent mosquitoes entering the tank).
Post storage filtration include such systems as the up flow sand filter or the twin compartment candle filters
commonly found in LDC’s. Many other systems exist and can be found in the appropriate water literature.

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Figure 8: the WISY filter (downpipe and high-capacity below ground versions) - Source: WISY Catalogue

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Sizing the system
Usually, the main calculation carried out by the designer when planning a domestic RWH system will be to size
the water tank correctly to give adequate storage capacity. The storage requirement will be determined by a
number of interrelated factors. They include:
1. local rainfall data and weather patterns
2. size of roof (or other) collection area
3. runoff coefficient (this varies between 0.5 and 0.9 depending on roof material and slope)
4. user numbers and consumption rates
The style of rainwater harvesting i.e. whether the system will provide total or partial supply (see the next
section) will also play a part in determining the system components and their size.
There are a number of different methods used for sizing the tank. These methods vary in complexity and
sophistication. Some are readily carried out by relatively inexperienced, first-time practitioners while others
require computer software and trained engineers who understand how to use this software. The choice of
method used to design system components will depend largely on the following factors:
1. the size and sophistication of the system and its components
2. the availability of the tools required for using a particular method (e.g. computers)
3. the skill and education levels of the practitioner / designer
Below we will outline 3 different methods for sizing RWH system components.
Method 1 – demand side approach
A very simple method is to calculate the largest storage requirement based on the consumption rates and
occupancy of the building.
As a simple example we can use the following typical data:
Consumption per capita per day, C = 20 liters
Number of people per household, n = 6
Longest average dry period = 25 days
Annual consumption = C x n = 120 liters
Storage requirement, T = 120 x 25 = 3,000 liters
This simple method assumes sufficient rainfall and catchment area, and is therefore only applicable in areas
where this is the situation. It is a method for acquiring rough estimates of tank size.

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Method 2 – supply side approach
In low rainfall areas or areas where the rainfall is of uneven distribution, more care has to be taken to size the
storage properly. During some months of the year, there may be an excess of water, while at other times there
will be a deficit. If there is enough water throughout the year to meet the demand, then sufficient storage will
be required to bridge the periods of scarcity. As storage is expensive, this should be done carefully to avoid
unnecessary expense. This is a common scenario in many developing countries where monsoon or single wet
season climates prevail.
The example given here is a simple spreadsheet calculation for a site in North Western Tanzania. The rainfall
statistics were gleaned from a nurse at the local hospital who had been keeping records for the previous 12
years. Average figures for the rainfall data were used to simplify the calculation, and no reliability calculation is
done. This is a typical field approach to RWH storage sizing.
The example is taken from a system built at a medical dispensary in the village of Ruganzu, Biharamulo District,
Kagera, Tanzania in 1997.
Rainwater harvesting Practical Action
Demand:
Number of staff: 6
Staff consumption: 25 lpcd*
Patients: 30
Patient consumption : 10 lpcd
Total daily demand: 450 liters
Supply:
Roof area: 190m
2
Runoff coefficient** (for new corrugated GI
roof): 0.9
Average annual rainfall: 1056mm per year
Daily available water (assuming all is
collected) = (190 x 1056 x 0.9)/ 365 = 494.7
liters
In this case, it was decided to size the tank to suit the supply, assuming that there may be growth in numbers
of patients or staff in the future. Careful water management will still be required to ensure water throughout
the year.
Demand:
Number of staff: 6
Staff consumption: 25 lpcd*
Patients: 30
Patient consumption : 10 lpcd
Total daily demand: 450 liters
Supply:
Roof area: 190m
2
Runoff coefficient** (for new corrugated GI
roof): 0.9
Average annual rainfall: 1056mm per year
Daily available water (assuming all is collected) =
(190 x 1056 x 0.9)/ 365 = 494.7 liters

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Figure 10 shows the comparison of water harvested and the amount that can be supplied to the
dispensary using all the water which is harvested. It can be noted that there is a single rainy season.
The first month that the rainfall on the roof meets the demand is October. If we therefore assume that
the tank is empty at the end of September we can form a graph of cumulative harvested water and
cumulative demand and from this we can calculate the maximum storage requirement for them
dispensary.

22
Figure 10: Comparison of the harvestable water and the demand for each month-
In this case the solution was a 50 cubic meterFerro cement tank-

23
Method 3 – computer model
There are several computer-based program for calculating tank size quite accurately. One such program,
known as sintex Tank, has been written by an Indian organization and is available free of charge on the World
Wide Web. The Ajit Foundation is a registered non-profit voluntary organization with its main office in Jaipur,
India and its community resource center in Bikaner, India.
User behaviour patterns with domestic RWH
Styles of RWH – system, climate and geographical variables
Rainwater that has been harvested is used in many different ways. In some parts of the world it is used merely
to capture enough water during a storm to save a trip or two to the main water source. Here, only small
storage capacity is required, maybe just a few small pots to store enough water for a day or half a day. At the
other end of the spectrum we see, in arid areas of the world, systems which have sufficient collection surface
area and storage capacity to provide enough water to meet the full needs of the user. Between these two
extremes exists a wide variety of different user patterns or regimes. There are many variables that determine
these patterns of usage for RWH.
Some of these are listed below:
Rainfall quantity (mm/year)
1. Rainfall pattern - The type of rainfall pattern, as well as the total rainfall, which prevails will
often determine the feasibility of a RWHS. A climate where rain falls regularly throughout the
year will mean that the storage requirement is low and hence the system cost will be
correspondingly low and vice versa. More detailed rainfall data is required to ascertain the
rainfall pattern. The more detailed the data available, the more accurately the system
parameters can be defined.
2. Collection surface area (m
2
)
3. Available storage capacity (m
3
)
4. Daily consumption rate (liters/capita /day or lpcd)- this varies enormously – from 10 – 15 lpcd
a day in some parts of Africa to several hundred lpcd in some industrialized countries. This
will have obvious impacts on system specification.
5. Number of users - again this will greatly influence the requirements.
6. Cost– a major factor in any scheme.
7. Alternative water sources– where alternative water sources are available, this can make a
significant difference to the usage pattern. If there is a groundwater source within walking

24
distance of the dwelling (say within a kilometer or so), then a RWHS that can provide a reliable
supply of water at the homestead for the majority of the year, will have a significant impact to
lifestyle of the user. Obviously, the user will still have to cart water for the remainder of the year,
but for the months when water is available at the dwelling there is a great saving in time and
energy. Another possible scenario is where rainwater is stored and used only for drinking and
cooking, the higher quality water demands, and a poorer quality water source, which may be near
the dwelling, is used for other activities.
8. Water management strategy– whatever the conditions, a careful water management strategy
is always a prudent measure. In situations where there is a strong reliance on stored
rainwater, there is a need to control or manage the amount of water being used so that it does
not dry up before expected.
We can simply classify most systems by the amount of ‘water security’ or ‘reliability’ afforded by the
system. There are four types of user regimes listed below:
Occasional - water is collected occasionally with a small storage capacity, which allows the user to
store enough water for a maximum of, say, one or two days. This type of system is ideally suited to a
climate where there is a uniform, or bimodal, rainfall pattern with very few dry days during the year
and where an alternative water source is available nearby.
Intermittent – this type of pattern is one where the requirements of the user are met for a part of the
year. A typical scenario is where there is a single long rainy season and, during this time, most or all
of the users’ needs are met. During the dry season, an alternative water source has to be used or, as
we see in the Sri Lankan case, water is carted/ bowered in from a nearby river and stored in the RWH
tank. Usually, a small or medium size storage vessel is required to bridge the days when there is no
rain.
Partial – this type of pattern provides for partial coverage of the water requirements of the user during
the whole of the year. An example of this type of system would be where a family gather rainwater to
meet only the high-quality needs, such as drinking or cooking, while other needs, such as bathing and
clothes washing, are met by a water source with a lower quality.
Full – with this type of system the total water demand of the user is met for the whole of the year by
rainwater only. This is sometimes the only option available in areas where other sources are
unavailable. A careful feasibility study must be carried out before hand to ensure that conditions are
suitable. A strict water management strategy is required when such a system is used to ensure that
the water is used carefully and will last until the following wet season.
Rainwater quality and health
Rainwater is often used for drinking and cooking and so it is vital that the highest possible standards are met.
Rainwater, unfortunately, often does not meet the World Health Organization (WHO) water quality guidelines.
This does not mean that the water is unsafe to drink. Gould and Nissen-Peterson(1999), in their recent book,
point out that the Australian government have given the all clear for the consumption of rainwater ‘provided
the rainwater is clear, has little taste or smell, and is from a well-maintained system’. It has been found that a
favorable user perception of rainwater quality (not necessarily perfect water quality) makes an enormous
difference to the acceptance of RWH as a water supply option.
Generally the chemical quality of rainwater will fall within the WHO guidelines and rarely presents problems.
There are two main issues when looking at the quality and health aspects of DRWH:

25
Firstly, there is the issue of bacteriological water quality. Rainwater can become contaminated by faces
entering the tank from the catchment area. It is advised that the catchment surface always be kept clean.
Rainwater tanks should be designed to protect the water from contamination by leaves, dust, insects, vermin,
and other industrial or agricultural pollutants. Tanks should be sited away from trees, with good fitting lids and
kept in good condition. Incoming water should be filtered or screened, or allowed to settle to take out foreign
matter (as described in a previous section). Water which is relatively clean on entry to the tank will usually
improve in quality if allowed to sit for some time inside the tank. Bacteria entering the tank will die off rapidly
if the water is relatively clean. Algae will grow inside a tank if sufficient sunlight is available for photosynthesis.
Keeping a tank dark and sited in a shady
spot will prevent algae growth and also keep the water cool. As mentioned in a previous section, there are a
number of ways of diverting the dirty ‘first flush’ water away from the storage tank. The area surrounding a
RWH should be kept in good sanitary condition, fenced off to prevent animals fouling the area or children
playing around the tank. Any pools of water gathering around the tank should be drained and filled.
Gould points out that in a study carried out in north-east Thailand 90 per cent of in-house storage jars were
contaminated whilst only 40% of the RWH jars were contaminated. This suggests secondary contamination
(through poor hygiene) is a major cause of concern.
Secondly, there is a need to prevent insect vectors from breeding inside the tank. In areas where malaria is
present, providing water tanks without any care for preventing insect breeding can cause more problems than
it solves. All tanks should be sealed to prevent insects from entering. Mosquito proof screens should be fitted
to all openings. Some practitioners recommend the use of 1 to 2 teaspoons of household kerosene in a tank of
water which provides a film to prevent mosquitoes settling on the water.
There are several simple methods of treatment for water before drinking.
1. Boiling water will kill any harmful bacteria which may be present
2. Adding chlorine in the right quantity (35ml of sodium hypochlorite per 1000 liters of water) will
disinfect the water
3. Slow sand filtration will remove any harmful organisms when carried out properly
4. A recently developed technique called SODIS (SolarDisinfection) utilizes plastic bottles which are filled
with water and placed in the sun for one full day. The back of the bottle is painted black. More
information can be found through the Resource Section at the end of this document
Quality of water
Whether given water is suitable for a particular purpose depends on the criteria or standards of acceptable
quality for that use. The physical as well as chemical quality of water is important to decide its suitability
for drinking purpose. Various standards are formulated by National and International agencies such as
WHO, ICMR, PHE Committee and all the standards are recommendatory and provide guidelines for
deciding the requirements. Rain water samples were collected from project sites during the rainy season and
analyses. The parameter analyzed included ph, conductivity, total dissolved solid, total hardness, calcium,
magnesium, chloride,, sodium etc. The analysis was carried out to know range of the parameters contained
in rain water and compare with the standards recommended by various agencies. The data generated by
analysis of water samples are shown below.

27
Chapter.6
HYDROLOGICAL ANALYSIS-
On the basis of experimental evidence, Mr. H. Darcy, a French scientist enunciated in 1865, a law
governing the rate of flow (i.e. the discharge) through the soils. According to him, this discharge
was directly proportional to head loss (H) and the area of cross-section (A) of the soil, and
inversely proportional to the length of the soil sample (L). In other words,
Q . A Q = Runoff
Here, H/L represents the head loss or hydraulic gradient (I), K is the co-efficient of permeability
Hence, finally, Q = K. I. A.
Similarly, based on the above principle, water harvesting potential of the catchment area was
calculated.
The total amount of water that is received from rainfall over an area is called the rainwater legacy
of that area. And the amount that can be effectively harvested is called the water harvesting
potential. The formula for calculation for harvesting potential or volume of water received or
runoff produced or harvesting capacity is given as:-
Harvesting potential or Volume of water Received (m3)
= Area of Catchment (m2) X Amount of rainfall (mm) X Runoff coefficient
Runoff coefficient for any catchment is the ratio of the volume of water that runs off a surface to
the volume of rainfall that falls on the surface. Runoff coefficient accounts for losses due to
spillage, leakage, infiltration, catchment surface wetting and evaporation, which will all
contribute to reducing the amount of runoff. Runoff coefficient varies from 0.5 to 1.0. In present
problem statement, runoff coefficient is equal to 1 as the rooftop area is totally impervious.

28
METHODS FOR STORAGE OF HARVESTED RAINWATER IN TANK-
Finally, we need to store the water which is obtained from the rooftop areas of the different
buildings. The volume of tank which stores the harvested water will be directly proportional to
the total volume of water harvested.
Technically, there are two types of methods for distributing the harvested rainwater:-
1. RATIONING METHOD (RM)
2. RAPID DEPLETION METHOD (RDM)
To explain these both methods, let us first apply it on any hall say M.S.S. hall. The detail
calculation is carried out to get the valuable steps. Later on, these crucial steps are again applied
to all other building and number of days for consumption of stored water is calculated by using
both of these methods.
1. RATIONING METHOD (RM)-
The Rationing method (RM) distributes stored rainwater to target public in such a way that the
rainwater tank is able to service water requirement to maximum period of time. This can be done
by limiting the amount of use of water demand per person.
Suppose in this method, the amount of water supplied to student is limited which is equal to say,
100 lt/day per capita water demand.
Again, Number of students at M.S.S. HALL = 300
Then, Total amount of water consumption per day = 300x0.1 = 30 m3/day
Total no. of days we can utilize preserved water = stored water/water demand
For M.S.S. Hall (Sample hall), volume of water stored in tank was taken approx. = 3600 m3
Hence finally, no of days = 3600/30 = 120 days (or 4 months)
For long term storage of preserved water in good condition, preserving chemical should be added.
2. RAPID DEPLETION METHOD (RDM)-
In Rapid Depletion method, there is no restriction on the use of harvested rainwater by consumer.
Consumer is allowed to use the preserved rain water up to their maximum requirement, resulting
in less number of days of utilization of preserved water. The rainwater tank in this method is
considered to be only source of water for the consumer, and alternate source of water has to be
used till next rains, if it runs dries.
For example if we assume per capita water demand = 150 lt/day = 0.15 m3/day
Total amount of water consumption per day = 300 x 0.15= 45m3/day
Total no. of days, preserved water can be utilize = stored water/water demand
= 3600/45
= 80 days (2.67 months)
Hence, finally it is observed that, if the amount of water stored is equal to 3600 m3, then applying
1. RDM, consumer can only utilize the preserved stored water for about 80 days (2.67 months),
2. Where as in RM, preserved stored water can be utilized for a period of 120 days (4 months).

29
OPTIMISTICDETERMINATIONOF SIZE & TYPES OF TANK-
COMPUTATION OF VOLUME OF RUNOFF PER YEAR:As we know the formula for runoff
discharge –
Volume of water Received (m3) = Area of Catchment X Amount of Rainfall

30
Chapter.7
TYPES OF TANK:
Two type of tank can be used for storing of rainwater discharged from the roof
1. LINED STORAGE TANK
2. UNLINED NATURAL STORAGE TANK
In lined storage tank, earth work excavation is done and underground RCC water storage tank is
constructed which is completely covered from the top. The land above the tank can be used for
serving as playground or parking slot, etc. In unlined natural storage tank, earth excavation is
done and all the water being allowed to fall directly in that pit and store it. In this method, we get
two advantages.
Firstly, our natural water gets recharged leads to augmentation of water level and ground
condition, increasing prospects for better future cultivation and plantation. Secondly,
underground water can be extracted anywhere within some limited areas from that pit and can be
used to satisfy daily water demand.

31
DETAIL ANALYSIS & DESIGNING OF RAINWATER HARVESTING SYSTEM
COMPONENT-
In this section, all the component of rainwater harvesting system is to be designed for all the
buildings located inside the campus .
Hence to start of, a sample calculation was done on a sample hall say M.S.S. hall, which will
draw the steps which has to be followed by all other building for designing its system
components.
Hence given below the complete design of all the components of rainwater harvesting of vit east
jaipur whose dimensions are mentioned in the figures 7 and tank size is 4 X 5 X 12.
ANALYSIS & DESIGN OF UNDERGROUND SUMP
Problem Statement :
Height of tank= 4m
Area of base = 60m2
Taking subsoil consists of sand, angle of repose = 30®
Saturated unit weight of soil = 17 K/m3
Water table likely to rise up to ground level
M20 concrete, HYSD bar
Unit weight of water = 9.81 KN/m3
Solution:
There are four components of design:-
i) Design of long wall
ii)Design of short wall
iii)Design of roof slab
iv)Design of base slab
GERNERAL
Design of wall be done under two condition:-
a) Tank full with water, with no earth fill outside
b) Tank empty with water, with full earth pressure due to saturated earth fill.
41 Department of Civil Engineering,
The base slab will be design for uplift pressure and the whole tank is to be tested against floatation.
Taking size of the base of tank =12X5m
As length (L)=12m
Breadth(B)=5m
L/B=12/5=2.3{>2} , Hence long wall be designed as a cantilever.
Bottom H/4 =4/4 = 1m of short wall be designed as cantilever , while
Top portion will be design as slab supported by long walls.
2. DESIGN CONSTANT
For M20 concrete, бcbc=7N/mm2 , m=13
Since face of wall will be in contact with water for each condition,
Бst=15N/mm2 for HYSD bar.
Permissible compressive stress is steel under direct compression = Бsc = 175 N/mm2
For Бcbc = 7 N/mm2 ,Бst = 150 N/mm2 , m= 13 ,
We have, K = = 0.378
J= 1-(0.378/3) = 0.874
R = 1/2 X 7 X 0.874 X0.378 = 1156
3. DESIGN OF LONG WALL

32
a) Tank Empty with pressure of saturated soil from outside
Pa = KaγH+γwH
γ = = 1/3
γ‟ =17-981=7.19 Kn/m3 = 7190 n/m3
γw = 9.81 Kn/m3
Pa = (1/3)X7190X4 + 9810X4 = 48,426.67 N/m2
Maxm. B.M. @ base of wall = 48,426.67 X (4/2)X (4/3) = 130,204.44 nm
D= = 335.6mm
Provide total depth D= 380 mm
D = 380 -35 = 345 mm
Ast = = 2,878.75 mm2
Using 30mm Φ bar, spacing ==109.13mm
Hence, provide 20mm Φ bar @ 100mm c/c on the outside face @ bottom of long wall.
CURTAILMENT OF REINFORCEMENT
Since the B.M. is proportional to h3
Asth/Ast = (h/H) 3 from which, h= H(Asth/Ast) ^(1/3)
If Asth = 1/2XAst (I.e. half of bar being curtailed)
h= H(1/2)^(1/3) = 4(1/2)^(1/3)=3.17 m
Height from base = 4-3.17 = 820 mm
Height as per code, IS 456, bar should contain further for a distance of 12Φ or d (which ever more)
12 XΦ = 12X 12 = 240
D=345mm,
So bar curtailed @ distance from the base = 820+345 = 1.17m
Min % of reinforcement = 0.3 – 0.1 = 0.23 %
Min Ast = 0.23X380X1000/100=879.43mm2
So, curtailment @ 1.17m from the base = 0.5XAst = 0.5 X 28787 =1439.35 > 879.43 (O.K)
DISTRIBUTION REINFORCEMENT
Ast = 879.43 mm2
Area to be provided on each face = 879.43/2 = 439.72 mm2
Hence proving 10mm Φ @ spacing = 170mm
Taking spacing = 160mm on both face of long wall
DIRECT COMPRESSION IN LONG WALL
The earth pressure acting on short wall will cause compression in long wall, because top portion of
short wall act as slab support on long walls.
At h=1m(>H/4) above the base of short wall
Pa=Kaγ‟ (H-h)+γ w (H-h)
=(1/3)X7190(4-1)+9810(4-1) = 33,620N/m2
This direct compression developed on long wall is given by
Plc=Pa.B/2=33620X5/2 = 91,550 N {This will be taken by distribution steel & wall section.}
Rainwater Harvesting at N.I.T. Rourkela 2 0 1 0
43 Department of Civil Engineering, N.I.T. Rourkela
B>TANK FULL WIT H WATER & NO EARTH FILL OUTSIDE
P=γwh=9810x4
=39240 N/M2
M=P.H2/6 = 39,240 X42/6 = 104640 Nm
Ast = = 2,313.53 mm2
Using 20mm Φ @ spacing = = 135.7
Taking 20mm Φ @ spacing 130mm c/c @ inside face.
CURTAILMENT OF REINFORCEMENT
Asth/Ast = (h/H) 3 from which, h= H(Asth/Ast) ^(1/3)
If Asth = 1/2XAst (I.e. half of bar being curtailed)
h= H(1/2)^(1/3) = 4(1/2)^(1/3)=3.17 m
Height from base = 4-3.17 = 820 mm

33
Height as per code, IS 456, bar should contain further for a distance of 12Φ or d (which ever more)
12 XΦ = 12X 12 = 240
D=345mm,
So bar curtailed @ distance from the base = 820+345 = 1.17m
So, at the base, 20 mm Φ @ 130mm c/c
At top from 1.17m from base, 20mm Φ @ 260mm c/c
DIRECT TENSION ON LONG WALL:-
Since the top portion of short wall act as slab supported on long wall, the water pressure acting on
short wall will cause tension in long wall:-
Pl=P.B/2 = 9810 X 3X 5/2 = 73, 575 N
As req. = 73,575/150 = 490.5mm2
Area of distribution steel (=879.43 mm2) will take direct tension.
4.DESGIN OF SHORT WALLS
A) TANK EMPTY WITH EARTH PRESSURE FRON OUTSIDE
I) TOP PORTION
The bottom 1m (H/4) act as cantilever while the remaining above 3m act as slab on long wall
At, =1m, above base of short wall,
Pa-= Kaγ‟ (H-h)+γ w (H-h)
=(1/3)X 7190X3 + 9810 X 3 = 36,620 N/m2
Mf@ support = PaL^2/12 = 36,620 X 5^2 / 12 = 76,291.67 Nm
This causes tension outside.
Mf @ centre = PaL2/8 – Mf = 36,620 X 52 (1/8- 1/12) = 38,145.83 Nm
d= 380 –(25+20+10) = 325 mm
At support, Ast = = 1790.57mm2
Using 16mm Φ bar Ast = = 116.7mm
So providing 16mm Φ bar@ spacing 110mm c/c @ outer face.
At mid span, Ast = (0.5X1790.57 = 895.285 mm2
Providing 16mm Φ @ spacing = 223.3 .i.e. providing 220mm c/c at inner face.
II)BOTTOM PORTION
The bottom 1m will bend as cantilever.
Intensity of earth pressure @ bottom = 48,826.67 N/m2 (from step 3)
M = 0.5X 48,826.67X1X (1/3) = 8137.78 Nm
Ast = = 179.92 mm2
Minm. Steel @ 0.23% = 879.43 mm2
So, Ast = Astminm.
Spacing of 12mm Φ = = 128.5 .i.e. 120 mm c/c
Hence providing 12mm Φ bar @ spacing 120mm c/c at the outside face in vertical direction for
bottom 1m height.
DIRECT COMPRESSION IN SHORT WALL
Only one meter of long pushes the short wall due to earth pressure, Pbc = PaX1 =36,620n
This compression is being taken up by distribution reinforcement.
B)TANK FULL WITH WATER AND NO EARTH FILL OUTSIDE
i)TOP PORTION
P=W(H-h) = 9810 X3 = 29,430 N/m2
Mf @ support = PB2/12 = 29430 X 5^2 / 12 = 61,312.25 Nm causing tension at the inside.
Mc @ centre = PB2/24 = 0.5 X 61,312.5 = 30,656.25 Nm causing tension at the outside.
Direct tension on short wall due to water pressure on the end 1meter of long wall
P b =W(H-h) X 1

34
=29,430 X1 = 29430 N
Effective depth d, for horizontal steel= 325mm @ distance x = d-D/2 = 325 – 380/2
= 135 mm
Ast1 = M-Pbx/Бstjd
Ast2 = Pb/бs
AT INSIDE FACE (END OF SHORT WALL)
Ast1 =– = 1345.8mm2
Ast2 = 29430 / 150 = 196.2 mm
Total = 196.2+1345.8 = 1542 mm2
Using 12mm Φ bar, spacing = 1000X113/1542 = 75 mm c/c.
AT OUTSIDE FACE (MIDDLE OF SHORT WALL)
Ast1 =– = 636.26mm2
Ast2 = 29430 / 150 = 196.2 mm
Total = 196.2+636.26= 822.46 mm2
Using 12mm Φ bar, spacing = 1000X113/822.46 = 120 mm c/c @ outside face.
i)BOTTOM FACE
P (from step 3b)= 39240 N/m2
Mf 0.5X(1/3)X 39240 = 6540 Nm causing tension at the inside.
Mc @ centre = PB2/24 = 0.5 X 61,312.5 = 30,656.25 Nm causing tension at the outside.
Ast = = 144.6 mm 2
But min. Steel req. = 879 mm2
So providing 12mm Φ bar @ spacing 120mm c/c.
SUMMARY OF REINFORCEMENT IN SHORT WALL
Taking of maxm out of both case 4A and 4B
I) Horizontal reinforcement @ inner face = 16mm Φ @ 75mm c/c
I) Horizontal reinforcement @ outer face = 16mm Φ @ 110mm c/c
III) Vertical reinforcement @ inner face & outer face = 12mm Φ @ 120mm c/c
5.DESIGN OF TOP SLAB
L/B = (12/5 ) = 2.4 (> 2) i.e. one way slab
Let live load on top slab = 2000 N/m2
Assuming thickness of 200mm including finishing ,etc.
Self weight = 0.2 X 1X1X 25,000 = 5000 N/m 2
Total weight = 2000+5000 = 70000 N/m2
M = WB^2 / 8 = 7000(5+0.38) 2 / 8 = 25,326.35 Nm
D= = 140mm
Providing a total thickness (D) = 180mm
d = 180-25-6 = 149 mm
Ast = = 1302.5 mm2
Spacing of 16mm Φ = 1000X201/1302.5 = 150 mm c/c @ outside face.
DISTRIBUTION REINFORCEMENT
Pt % = 0.3 – 0.1 X = 0.277%
Spacing of 10mm Φ bar = 1000 X 78.54 / 415.7 = 180 mm c/c
6.DESIGN OF BOTTOM SLAB
Magnitude of uplift pressure, Pu = WH1= 9810 X 4.3 = 42,183 N/m2
A) CHECK FOR FLOATION
Check is done when tank is empty.
Total upward floatation force = P = Pu X B X L = 42183X5X12 = 2530980 N
Total Downward force = weight of wall + (weight of roof slab + finishes) + weight of base slab

35
= [0.38(5+5+12+12) X4.3X25000] + [ 0.2X 5X12X25000] + [ 5X12X0.3X25000]
= 2138900N
Weight of roof so downward force is less than buoyant force, we need to provide extension of 0.5 m
on both side.
Extra weight req. = 2530980-2138900 = 392080N
By extending 0.5 on both side, extra weight of tank
= [(0.5 x 5 X 2) + (0.5 X 12 X 2) + (0.5 X 0.5 X 4)] X 25000 X 0.3= 135000 N
Weight of soil = [(0.5 x 5 X 2) + (0.5 X 12 X 2) + (0.5 X 0.5 X 4)] X 17000 X 4= 1224000 N
Total = 1359000N (safe)
B)DESIGN OF BASE SLAB
Considering 1m length of slab, upward water pressure = 42183N/m2
Self weight of slab = 1 X 1 X 0.3 X 25000 = 7500 N/m2
Net upward pressure, P = 34683 N/m2
Weight of roof slab per meter run = 0.2 (2+0.38)X1X25000 = 11900 N
Weight of wall / meter run = 0.38X4X1X25000 = 38000 N
Weight of earth projection = 1700 X 4 X 1 X 0.5 = 34000 N/m
Net unbalance force / meter run = 34683 (6.286 X 1) – 2 (38000 +11900 + 34000) = 50217.3N
Reaction on each wall = 50217.3/2 = 25108.67 N
Pa = Kaб‟ H + wH = 48826.67 N/m2
Pa =48826.67 X(4/2) X 1 = 97653.34 Nm acting @ (4/3)+0.3 = 1.66 m from the bottom of base
slab
B.M. @ edge of cantilever portion = (34683 X 0.5 2 / 2 )+ 25108.67 X1.66- (1700X4X0.52/2)
= 45165.76Nm causing tension @ bottom face.
B.M @ centre of span = ((34683/2)X (6.286) 2/4) + 97653.34X1.66 –
(38000+11900+25108.67)X4.38/2 -1700X4X0.5(6.38/2-0.25) = 234044.7 Nm
d = = 450 mm, so keeping D = 500 mm , d = 450 mm
Ast = = 7140.1 mm2
Providing 24mm Φ bar spacing = 1000X 452.4 / 7140 = 65 mm c/c
Distribution reinforcement in longitudinal direction = 0.3 – 0.1[]= 0.243 % Area o n steel = 0.243 X
1000X300/100 = 729 mm2
Area on steel on each face = 729 /2 = 364.5 mm2
Spacing of 8mm Φ bar = 1000X 50.3 / 364.5 = 138 mm
Provide 8 mm Φ bar @ 130 mm c/c on each face.
DETAIL COST ESTIMATION OF SUMP (UNDERGROUND TANK)
Finally cost of entire project play a crucial role in any type of project. Before implementing the
project, it is highly necessary for the engineers to check project, whether it is economical or not.
Hence, the detail cost estimation should be done.
Tank shall be of first class brickwork in 1:4 cement mortar foundations and floor shall be of 1:3:6
cement concrete. Inside of septic tank shall be finished with 12mm cement plaster and floor shall be
finished with 20mm cement plaster with 1:3 mortar mixed with standard water proofing compound.
Upper and lower portion of soak-pit shall be of second class brickwork in 1:6 cement mortars and
middle portion shall be of dry brickwork. Wall thickness is about 30cm.

36
Chapter.8
DETAIL COST ESTIMATION OF SUMP (UNDERGROUND TANK) –
Finally cost of entire project play a crucial role in any type of project. Before implementing the
project, it is highly necessary for the engineers to check project, whether it is economical or not.
Hence, the detail cost estimation should be done.
Tank shall be of first class brickwork in 1:4 cement mortar foundations and floor shall be of 1:3:6
cement concrete. Inside of septic tank shall be finished with 12mm cement plaster and floor shall
be finished with 20mm cement plaster with 1:3 mortar mixed with standard water proofing
compound. Upper and lower portion of soak-pit shall be of second class brickwork in 1:6 cement
mortars and middle portion shall be of dry brickwork. Wall thickness is about 30cm. Roof
covering slabs shall be precast R.C.C. The length of the connecting pipe from latrine seat may be
taken as 3 meters. And suitable rates are assumed.
Given below the detail cost estimation of constructing an underground sump of dimensions (4 x 5
x 12) at hostel site:

37
Hence, after studying the present market value of material required for constructing the entire tank
and using it while calculating during costing and estimation of tank. After all several steps, the total
cost of tank was came out to be Rs. 7,17,685.80. This steps was applied to all other building for
determining the final cost price of the tank.
FIRST FLUSH MECHANISMS
First flush mechanism is shown in the fig8. Due to long dry period, the catchment area generally gets
dirty. Hence in order to prevent entry of excess dirt from the catchment area from entry into tank and
polluting the water, first flush mechanism is designed. And the order of this mechanism becomes
highly important when water preserved is utilized for drinking purpose. Turbidity factor was also
considered while design first flush mechanism. After studying our requirement and prevailing
condition, the design value of this mechanism was fixed to be 8liters/10m2. And finally Ball-Valve
design was chosen. Ball-Valve design has a unique mechanism for controlling the flow of water into
and outside of the tank. Ball-Valve design is shown in the figure. This system consists of ball inside
the specially designed pipe which opens and closes the opening of outlet to the storage tank and
diversion chamber according the level of water. When the water fills up to the brim, the water is
diverted to the main tank from the side outlet. And when the water needs to be rejected is sent to the
small diversion chamber where it fills the inlet pipe.
Ball Valve Type First-Flush Mechanism
the diversion chamber and the pipe up to the Ball-Valve are carefully designed to match the
diversion volume that is calculated. The connection between the terrace water and storage tank
rebuilds when water reaches the level of the ball making the ball to float and block the connection
between the terrace water and diversion chamber, thus sending the water back again to main
storage tank. In this way, Small diversion chambers are designed for the downpipes from each
terrace. The diversion tank can have a tap which may be operated.

38
Filtration
Filtration is highly required for the rainwater which is harvested from the rooftop area. When
water is use for drinking purpose then this process become even more important. But, basic
filtration is preferable required to avoid excessive dirt entering the system. A very simple, cost-
effective mechanism has been chosen preferred overelaborate commercial systems. Leaf and twig
screen, for basic which is a 5mm thick mesh with wire frame running along the gutters was
selected. With most of the commercial fine filtration systems, there is a general difficulty of
handling high flow rates, thus, a practical filtration method was selected running the flow through
a fine cloth/mosquito net mesh. The flow rate would not be impeded much; it’s very cost
effective and can be easily maintained and replaced. Again, two cloth filters for hydraulic and
cleaning efficiency using a graded sand load can be chosen whose results are highly comparable
to commercial filters.

40
CONCLUSION
This paper dealt with all aspect of improving the water scarcity problem in the vit campus by
implementing ancient old technique of rainwater Harvesting. Two alternatives have been suggested
for tank design, which takes separate approaches towards the consumption of harvested rainwater.
These results are given clearly in the table. Hence from this table, we can draw out a conclusion that a
huge amount of water got collected from the rooftop surfaces of all the entire buildings. And if, this
project is being done seriously and implemented to the campus then R5 (behind Mechanical) has a
huge harvesting potential. This reservoir should have to build for the storage of 9942.1 m3 of water.
Hence this tank has huge capacity of getting rainwater and on proper storage, this tank can supply
almost throughout the year for about 300 consumers having a consuming rate of 100liter/day as
calculated by rational depletion method. The water has almost the potential amount of tank-
Reservoir capacity (m3) No. of days of potential by
Rational Methods
No. of days of potential by
Rapid depletion method
9942.1(R5) 331.40 220.93
Tank cost – Rs. 717685.8

Rainwater harvesting

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Rainwater harvesting