Investigating the Potentials of Rainwater Harvesting System in Melbourne and Adelaide

This study aims to investigate the potential of rainwater harvesting systems in Melbourne and Adelaide. The study will create a water balance model to determine if rainwater harvesting systems are a reliable alternative for water shortage in the two cities. The paper will use software to create a model that can be used to estimate the volume of rainwater that can be harvested using different rainwater harvesting systems.

POTENTIALS OF RAINWATER HARVESTING 1
INVESTIGATING THE POTENTIALS OF THE RAINWATER HARVESTING SYSTEM IN
MELBOURNE AND ADELAIDE
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Abstract
Many countries are facing the problem of water scarcity, which is expected to rise in the coming
years due to factor such as population growth and climate change. Australia is the driest
continent in the world and most of its cities are affected by water shortage. As a result, the need
for alternative water sources in Australian cities cannot be overemphasized. This study will focus
on determining the potential of rainwater harvesting system in Melbourne and Adelaide. This
will be achieved by creating a computerized simulation model with the ability to estimate the
amount of rainwater that can be harvested per unit roof area in Melbourne and Adelaide. The
amount of rainwater harvested depends on annual rainfall amount, and the type, size and
efficiency of rainwater harvesting systems used. Many Australian cities have turned to rainwater
harvesting systems as an alternative source of water to supplement mains supply. A water
balance model for Melbourne and Adelaide will be created and used to determine the percentage
of water demand that can be supplied with rainwater harvesting systems in the two cities. It is
expected that rainwater harvesting systems in Melbourne and Adelaide account for relatively
small percentage of water consumption in Melbourne and Adelaide. However, this model can be
used to determine ways on how to increase the amount of rainwater harvested.

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Table of Contents
Abstract......................................................................................................................................................2
1. Introduction.......................................................................................................................................4
1.1. Problem Statement....................................................................................................................5
1.2. Aim..............................................................................................................................................5
1.3. Objectives...................................................................................................................................6
1.4. Research Justification................................................................................................................6
1.5. Melbourne Rainfall....................................................................................................................7
1.6. Adelaide Rainfall.......................................................................................................................9
2. Literature Review............................................................................................................................11
2.1. Components of a rainwater harvesting system......................................................................12
2.2. Functions of rainwater harvesting systems............................................................................12
2.3. Types of rainwater harvesting systems..................................................................................13
2.4. Types of rainwater storage tanks............................................................................................14
2.5. Advantages and Disadvantages of Rainwater Harvesting Systems......................................20
2.5.1. Advantages.......................................................................................................................20
2.5.2. Disadvantages...................................................................................................................22
2.6. Estimation of Harvested Rainwater Volume.........................................................................23
2.7. Water Balance Model..............................................................................................................25
3. Methodology.....................................................................................................................................28
3.1. Study area.................................................................................................................................28
3.1.1. Melbourne........................................................................................................................28
3.1.2. Adelaide............................................................................................................................29
3.2. Google Earth............................................................................................................................29
3.3. Calculation of Roof Surface Area...........................................................................................30
3.4. Digitalized Areas Corrections.................................................................................................30
3.5. Estimation of Potential Volumes of Harvested Rainwater...................................................31
3.6. Estimation of Water Demand.................................................................................................31
3.7. Comparing Water Demand and Supply Gap........................................................................33
4. Conclusion........................................................................................................................................33
References................................................................................................................................................36

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1. Introduction
Water scarcity is a problem that is already affecting over 40% of the global population
(Reporter, 2018). This problem is expected to rise because of population growth, global warming
and climate change in general (Adugna, et al., 2018). Cities, which are already hosting about
55% of the world’s population (and this is expected to reach 68% by 2050) (Meredith, 2018), are
the most affected as the increasing urban population puts pressure on water reserves. The
reserves are also already stretched due to too much waste and too little rain (SBS News, 2018).
Australia is the driest continent on earth (Preston, 2008) hence the need for alternative water
harvesting systems and saving measures in the country is inevitable. Some of these include:
water conservation, water recycling, rainwater harvesting and desalination. This research focuses
on the potential of rainwater harvesting system in Melbourne and Adelaide.
Australia is the world’s driest inhabited continent, characterized by the lowest volume of
water in rivers, smallest area of perpetual wetlands and lowest run-off. Its climate is slowly
drying and has very high variability (Australian Government, 2018). Th highly variable climate
is due to atmospheric variation and different currents. The country has regular cycles of floods
and droughts that result in extremely variable water storage volumes especially in its major dams
(van der Sterren, et al., 2010). Human activities are continuously exerting pressure on marine
environments in the country, making water crisis a national problem.
Melbourne and Adelaide are among Australian cities that are feeling water stress
(Wright, 2017). Within a decade, these cities could experience water crisis. Water scarcity s
when there is <100 m3 deficit per capita per annum while water stress is when there is <1,700 m3
deficit per capita per annum (Taffere, et al., 2016). Melbourne’s water storage now stands at
58.4% from 62.1% the previous year, while Adelaide’s water storage is at 46.2% from last year’s

POTENTIALS OF RAINWATER HARVESTING 5
56.6% (Australian Government - Bureau of Meteorology, 2018). The continuing water shortage
in Melbourne and Adelaide is mainly caused by population growth and climate change
(Chalkley-Rhoden, 2017). Therefore the need for alternative water harvesting system in the two
cities is inevitable.
1.1. Problem Statement
Water plays a pivotal role in people’s day-to-day activities. Every government wishes to
supply citizens with adequate water for domestic, agricultural and industrial use. Adequate water
supply has positive impacts on people’s quality of life, environmental conservation and
economic growth. However, Australia, which is the world’s driest continent, is facing water
shortage problem. Melbourne and Adelaide are among the most affected cities. This problem is
mainly caused by climate change and the rapidly increasing urban population (Lee, et al., 2017).
As climate change intensifies and urban population continues to grow, water demand in both
cities will soon outstrip supply. As a result, water crisis is looming. However, this problem can
be alleviated by exploring alternative water sources. This study proposes to investigate the
potential of rainwater harvesting systems for increasing water supply in Melbourne and
Adelaide. The study will entail carrying out comprehensive investigation so as to create a water
balance model that can determine if rainwater harvesting systems is a reliable alternative for
water shortage in the two cities.
1.2. Aim
This study aims at investigating the potential of rainwater harvesting systems in
Melbourne and Adelaide, so as to determine if these systems can be used to alleviate water
scarcity in the two cities. This will be achieved by creating individual water balance models for
Melbourne and Adelaide.

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1.3. Objectives
The specific objectives of the study are:
 To evaluate and predict the potential of rainwater harvesting in Melbourne and Adelaide
 To determine the reliability of rainwater harvesting systems in Melbourne and Adelaide
 To assess the effects of Australia’s climatic condition variation on the efficiency and
reliability of rainwater harvesting systems in Melbourne and Adelaide
 To assess the amount of water used in Melbourne and Adelaide and determine if
rainwater harvesting systems are a feasible alternative for water scarcity
 To create a water balance model for the cities of Melbourne and Adelaide.
1.4. Research Justification
Water is very important to life (Alexe & Toma, 2013); (Popkin, et al., 2010). According
to the United Nations, people have a right to safe and clean drinking water. The water also plays
a key role in attaining other human rights such as livelihoods and food (Hall, et al., 2014).
However, factors such as population growth, inefficient water practices and climate change have
resulted to global water scarcity. Australia is among the most affected countries (considering also
that it is the driest continent on earth). The focus of this paper is on two Australian cities:
Melbourne and Adelaide. These cities are already experiencing water shortage and water crisis is
looming. In the near future, water demand will surpass water supply. In order to protect the lives
of residents, protect the environment (biodiversity and ecosystems) and promote economic
growth of Melbourne and Adelaide, the need for alternative water sources cannot be
overemphasized. This research will be examining the potential of water harvesting systems as an
alternative source of water for Melbourne and Adelaide. The paper will use software to create a
model that can be used to estimate the volume of rainwater that can be harvested using different

POTENTIALS OF RAINWATER HARVESTING 7
rainwater harvesting systems. This model can be used by the federal government, state
governments, local governments, companies and individuals to determine the most appropriate
type and size of water harvesting systems they can use to generate more water for various uses in
Melbourne and Adelaide. Most of the previous studies did not consider the specific
characteristics and variations of Melbourne and Adelaide, instead they created general models
for Australia, which does not provide accurate estimates for specific cities. This is because
rainwater harvesting is a site-specific source of water (Stout, et al., 2017). It is also worth noting
that the variability of Australian climatic conditions is very high hence the need to create specific
rainwater harvesting system models for each city. Findings from this research can be used by
policymakers in Melbourne and Adelaide to develop appropriate infrastructure and plans that
will promote use of rainwater harvesting systems thus increasing water supply in the two cities
and reducing overreliance on mains supply.
1.5. Melbourne Rainfall
Melbourne is located at an altitude of 35 m above sea level. Its climate is classified as
temperate oceanic (warm and temperate), and is known for its high variability due to
geographical location of the city. The city is located to the south hence it is affected by westerly
winds’ flow. These winds bring low pressure systems in different months of the year, which
causes climate variations. According to Koppen-Geiger climate classification system, the climate
of Melbourne is Cfb – a west coast marine climate (Denk, et al., 2013). Cfb represents a
generally humid climate with a sort dry summer. During mild winters, heavy precipitation occurs
due to presence of mid-latitude cyclones (PhysicalGeography.net, 2018). Koppen classification
system is classifies climate based on regions’ characteristics seasonalities and other multiple
variables (Chen & Chen, 2013).

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The climograph of Melbourne is as shown in Figure 1 below. The graph shows that
Melbourne receives significant amount of rainfall all year round, including the direst month. The
month with the lowest rainfall is February and March, which receives 44 mm each while the
month that receives the highest rainfall is October with 71 mm. The average annual rainfall is
666 mm while the average monthly rainfall is 55.5 mm. Generally, Melbourne does not receive
very abundant rainfall but the rainfall it receives is well distributed over the months
(Climatestotravel.com, 2018). The difference of rainfall received during the wettest and driest
months is 27 mm.
Figure 1: Climograph of Melbourne (Climate-Data.Org, (n.d.)b)
The warmest month of the year is February with an average temperature of 20.3°C
(February is also the month that receives the lowest rainfall) while the coldest month is July with
an average temperature of 9.4 °C (July is also the month that receives the highest rainfall). The
difference of temperature between the warmest and coldest months is 10.9 °C.

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1.6. Adelaide Rainfall
Adelaide is located at an altitude of 49 m above sea level. Its climate is classified as
Mediterranean climate (mild, warm and temperate). The city is the driest of all capital cities of
Australia (World Weather and Climate Information, 2016). The summer months receive less
rainfall than the winter months. The summer months of Adelaide are dry and warm while the
winter months are wet and mild. The summer usually runs from December to February, the
winter runs from June to August while spring runs from September to November. According to
Koppen-Geiger climate classification system, the climate of Adelaide is Csa – hot dry-summer
Mediterranean climate. Csa climate is mainly characterized by cool, wet winters and hot, dry
summers, and is located between latitude 30 °N and 45 °N, and the south of equator
(Encyclopedia Britannica, 2018).
The climograph of Adelaide is as shown in Figure 2 below. From the graph, it is seen that
Adelaide receives low rainfall during summer and some significant amount of rainfall during
winter. The month with the lowest rainfall is February, which receives 15 mm each while the
month that receives the highest rainfall is July with 76 mm. The average annual rainfall is 536
mm while the average monthly rainfall is 44.7 mm. Generally, Adelaide does not receive
abundant rainfall. Also, most of the rainfall is received during winter whereas summer months
receive very little rainfall. The difference of rainfall received during the wettest and driest
months is 61 mm.

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Figure 2 Climograph of Adelaide (Climate-Data.Org, (n.d.)a)
The hottest months of the year are January and February with an average temperature of
22.1°C (January and February are also the months that receive the lowest rainfall) while the
coldest month is July with an average temperature of 10.8 °C (July is also the month that
receives the highest rainfall). The difference of temperature between the hottest and coldest
months is 11.3 °C.
From the climographs of Melbourne and Adelaide above, it shows that Melbourne
receives more rainfall than Adelaide. This is because the average annual rainfall and average
monthly rainfall of Melbourne is 666 mm and 55.5 mm respectively while the average annual
rainfall and average monthly rainfall of Adelaide is 536 mm and 44.7 mm respectively. This
means that with all other factors held constant, the potential of rainwater harvesting is expected
to be high in Melbourne than in Adelaide.

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2. Literature Review
Water is a very essential natural resource for human, animal and plant life (Friedrich, 2015);
(Rietveld, et al., 2016). However, the water is gradually becoming scarce due to factors such as
population growth, economic growth and climate change (Amos, et al., 2016); (Traboulsi &
Traboulsi, 2017). Rainwater harvesting is a technique of collecting and storing rainwater
(Abdulla & Al-Shareef, 2009); (Tamaddun, et al., 2018). This method is considered to be ancient
but it is very important even today (Martin, et al., 2015); (Manikandan, et al., 2011). As a matter
of fact, rainwater harvesting is considered a viable option for reducing the gap between water
demand and supply (Lani, et al., 2018), in many cities across the world (Anon., 2013). It is an
inexpensive source of water in rural and urban areas (Al-Houri, et al., 2014).
Implementation of rainwater harvesting systems has significantly increased among
Australian households in recent years (australian Building Codes Board, 2016). Historically,
federal, state and local governments in Australia discouraged harvesting and use of rainwater.
However, this has changed over the recent years and many governments are now encouraging
rainwater harvesting and offering rebates to individuals and companies installing rainwater tanks
(Productivity Commission, 2011). Studies have also shown that majority of households are
installing rainwater harvesting systems in their homes so as to save water and reduce
overreliance on mains supply.
From the current trends, it is expected that uptake of rainwater harvesting systems in
Australia will continue growing. This is because rainfall across the Australian continent is
continuing to reduce and climatic conditions varying significantly hence the need for alternative
water sources is going to increase. Other factors that will promote uptake of rainwater harvesting
systems include: adoption of building regulatory requirements that encourage rainwater

POTENTIALS OF RAINWATER HARVESTING 12
harvesting; changes in pricing of water; and public awareness and education about recent
droughts that have prompted people to shift to rainwater harvesting so as to ensure steady supply
of water.
2.1. Components of a rainwater harvesting system
The main components of a rainwater harvesting system are a roof catchment, filter (for
removing runoff’s initial fraction), cistern (storage tank) and a pump (Sample, et al., 2013). The
roof collects water by the help of gutters that channel the water to downspouts. The water is then
passed through a filter and then piped to the storage tank. The water can then be directed to the
end users by gravity or propelled by a pump, depending on the design of the rainwater harvesting
system and the location of the end user. The rainwater storage tanks are available in different
designs (shapes and sizes), depending on factors such as roof area, local rainfall characteristics,
water demand, and availability or reliability of mains water. These tanks can also be made from
different materials, including coated corrugated iron or metal, concrete, tiles and polypropylene.
The best rooftops suitable for rainwater harvesting are those made of corrugated iron or metal,
followed by those made from tiles ad lastly concrete. Some storage tanks can also have a water
treatment system.
2.2. Functions of rainwater harvesting systems
A rainwater harvesting system has 6 key functions. These are:
Water collection: the system is used to collect or harvest rainwater from the roof using
gutters. The amount of water collected is directly proportional to the rainfall intensity and
surface area of the roof.

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Water transport: after collecting the water, the rainwater harvesting system transports it
via downspouts and piping, towards the storage tank.
Debris removal: the system also removes debris from the water by filtering. This is done
by passing the collected water through a filter or series of filters. The filtering is used to pre-
clean the water.
Water storage: the rainwater harvesting system also has a storage tank for storing the
collected water. The storage tank can be underground, on surface or at an elevated point.
Water pressurization: depending on the type of rainwater harvesting system, it may have
a pump for pressurizing the water so that it can be supplied to the final destination where it is
intended to be used.
Water disinfection: if the harvested rainwater is to be used for drinking, it must be treated
first (Abbasi, 2011). Therefore the rainwater harvesting system may have a water treatment
system to disinfect the water and make it potable (suitable for drinking).
2.3. Types of rainwater harvesting systems
There are different types of rainwater harvesting systems. Some of these include the following:
Direct-pumped (submersible) system: this is the commonest type of rainwater harvesting
system, mainly for domestic properties. In this system, the pump is installed in the underground
water storage tank. The harvested rainwater is then pumped directly from the tank to various
appliances such as WCs. The storage tank is connected to the mains water that feeds it when it is
about to run dry so as to maintain water supply.

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Indirect-pumped (suction) system: this system is similar to the submersible system only
that the pump is not located within the underground storage tank, instead it is located in a control
unit inside a utility room. The control unit is also connected to the mains water supply that
maintains water supply when the tank runs dry. Therefore water from the mains water supply is
not fed into the storage tank first but it is directly pumped to the water appliances.
Indirect gravity system: this system has a header tank (high level tank). First, the
harvested rainwater is pumped to the header tank. This water is then supplied to the outlets
through gravity only. In this system, the pump is only used when filling the header tank
otherwise flow of water from the tank to the appliances is by gravity. Additionally, the mains
water is directly fed to the header tank, instead of the main harvesting tank.
Indirect pumped system: this system is similar to the indirect gravity system only that the
internal tank does not have to be at an elevated point but can be placed at any level since water
supply to the outlets is not by gravity. Instead a pressurized supply is provided by a booster
pump. The system can be used in multi-storey buildings.
Gravity only system: this system does not have a pump and therefore no use of energy at
any point. The system operates through gravity only. In this system, the collection tank and filter
are located above all water outlets. This is the most energy-efficient rainwater harvesting system
(Rainharvesting Systems Ltd, 2018).
2.4. Types of rainwater storage tanks
Rainwater harvesting systems have tanks for storing the harvested rainwater. The tanks are
available in different sizes and shapes, and are made of different materials. The most common
types of rainwater tanks include the following:

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Concrete tanks: these tanks are made of concrete hence they are generally heavy, strong
and durable. Because of their heaviness, concrete tanks are usually installed underground. This
makes it expensive to excavate the ground but also helps in saving space in the garden. When
installing these tanks, it is important to know where the utilities are located, such as septic tanks.
There are two major types of concrete rainwater tanks: monolithic-pour tanks concrete and ferro-
concrete tanks. Monolithic-pour concrete tanks are those that are prefabricated in a factory and
transported to the site for assembling, or poured in place. Ferro-concrete tanks are those that are
made by spraying a special concrete mixture directly on a metal frame. Concrete tanks are also
susceptible to leaching of lime from the concrete into the tanks especially when the tanks are still
new. The leaching can cause the water to become alkaline making it unsuitable for most uses,
such as irrigation, cooking, bathing, etc. However, this can be prevented by using a lining on the
internal surface of the concrete tank. An example of a concrete rainwater tank is shown in Figure
3 below
Figure 3: A concrete rainwater tank (Rainharvest.co.za, 2010)
Metal tanks: these tanks are less expensive in comparison with concrete tanks. They are
lightweight and installed above the ground. The metal tanks are also easy to install. Fabrication

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of metallic water storage tanks is usually done using galvanized steel. The main disadvantage of
steel galvanized tanks is that they are susceptible to rusting. When they are exposed to moisture,
these tanks can rust thus affecting the quality of stored water. This problem can be prevented by
ensure proper galvanization of the tank to make it rust-proof. To avoid the problem of galvanized
steel, many manufacturers are using alternative metals such as aluminium. An example of a
metal water storage tank is shown in Figure 4 below
Figure 4: A metal rainwater tank (AgriLife Extension, 2018)
Polythene tanks: these are the most popular rainwater storage tanks because of their low
cost and they are very light hence can be transported from one place to another and installed
easily. The tanks can also be moulded into different shapes and sizes with ease. If these tanks are
exposed to extreme sunlight levels, they are likely to be affected by corrosion. These tanks are
usually molded around a central steel mould during manufacturing hence they usually come in
standard sizes and shapes (mostly circular). Examples of polythene tanks are shown in Figure 5
below

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Figure 5: Polythene rainwater tanks (Plastic Tanks Qld, 2016)
Bladder tanks: these tanks are characterized by a flexible membrane that makes it
possible to install in small space or an irregular space. When water enters the bladder, the
flexible membrane expands, and when water is drawn from the bladder, it contracts. Installation
of these tanks require an underground framework so as to prevent movement of the bladder
tanks. These tanks can also be installed vertically, such as in a frame against a wall or fence.
Generally, balder tanks are the most flexible rainwater storage tank alterative but they have the
most limited storage capacity. Therefore these tanks are a viable options for people with small
plots or few household members or low water demand. Examples of balder tanks are shown in
Figure 6 below

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Figure 6: Bladder rainwater tanks (Waterplex, 2018)
Fiberglass tanks: these tanks are made from fiberglass, which is resistant to rust.
Fiberglass is a polymer comprising of densely woven plastic strands reinforced with glass fibers.
The reinforcement ensures that the fiberglass is very strong. The fiberglass tanks are stronger
than most of the metal tanks. The fiberglass tanks are suitable for storing high volumes of
rainwater as their high tensile strength enables them withstand high pressure of large water
volume. However, the fiberglass tanks are usually more expensive than most of the other tanks
(Regenerative Corporation, 2017). An example of a fiberglass tank is shown in Figure 7 below
(Rainwater Rsources, 2013)
Figure 7: Fiberglass rainwater tank
Round corrugated tanks: these tanks are very strong and usually in a round shape. There
are two main categories of round corrugated tanks: small round tanks and large round tanks. The
small round tanks usually have a storage capacity ranging from 1,000 liters to 9,500 liters, while
the large round tanks usually have a storage capacity ranging from 10,000 liters to 46,800 liters.
An example of a round corrugated tank is shown in Figure 8 below (Auzzie Wrinkly Tin Tanks,
2018).

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Figure 8: Round corrugated rainwater tank
Slimline water tanks: these tanks are mainly used for storing rainwater intended for
industrial use. The slimline tanks are available in different shapes and sizes, making them
suitable for households with varied water needs. An example of a slimline tank is as shown in
Figure 9 below
Figure 9: Slimline rainwater tank (Taylor Made Tanks, 2018)
Underground water tanks: these tanks usually have a storage capacity ranging from 1,600
liters to 5,000 liters.

POTENTIALS OF RAINWATER HARVESTING 20
2.5. Advantages and Disadvantages of Rainwater Harvesting Systems
As clean water continues to become scarce worldwide, water bills are increasing gradually.
Water demand has also increased over the years and many households and businesses are
spending significant amount of their income and revenue on water bills. This has driven both
households and companies to turn to rainwater harvesting as an alternative source of water for
domestic and commercial uses. The rainwater harvesting systems have both advantages and
disadvantages. Some of these are discussed below
2.5.1. Advantages
Some of the key advantages of rainwater harvesting systems include the following:
Saves money: the scarcity of water has resulted to increased water bills in many cities,
including Melbourne and Australia. The harvested rainwater can be used in different ways
depending on its quality and quantity. Irrespective of how it is used, rainwater reduces the
overall water consumption thus lowering water bills.
Saves a valuable resource: water is a very valuable natural resource that human beings
cannot do without. Harvesting rainwater means saving it from being wasted. Instead of the
rainwater being washed away as runoff or being absorbed into the ground, it gets collected and
used in homes, farms or business premises. Therefore rainwater harvesting is a way of
preventing wastage of rainwater.
Improves biodiversity and ecosystems: rainwater harvesting systems reduces drawing of
water from rivers, seas, oceans and dams. It means that water from these sources will be
available for use by plants and aquatic animals. Thus rainwater harvesting helps in making water
available for animals and plants thus preserving and improving the environment.

POTENTIALS OF RAINWATER HARVESTING 21
Improves quality of health and life: water is life and human beings cannot survive
without it. Harvested rainwater can be used for washing, cleaning, cooking, irrigation, industrial
activities, etc. This water can also be treated and used for drinking. As a result, rainwater
harvesting systems makes people’s lives more comfortable and happier (Owusu & Teye, 2015).
Increases property value: homes installed with rainwater harvesting systems costs higher
because they guarantee water availability. Therefore rainwater harvesting systems is a form of
investment for homeowners. Once the system is installed, the value of the house goes up.
Enhance water reliability: with the right size of water storage and high collection
efficiency, a rainwater harvesting system can guarantee water available throughout the year. It is
normal to experience water shortages from mains supply due to factors such as low water levels
in reservoirs (especially during dry seasons), periodic maintenance of municipal water
distribution system, repairs of municipal water supply system, contamination of water from
mains supply, etc. But a rainwater harvesting system collects maximum water when it rains and
stores it in a storage tank for use, especially during dry seasons. This ensures steady supply of
water at all times.
Reduce stress on mains supply: rainwater harvesting systems are not only beneficial to
end users but also to governments. These systems reduce reliance on mains supply because
people can use rainwater harvested and stored in storage tanks. As a result, the mains supply
system can perform at its maximum efficiency and scheduled maintenance can be carried out
without much interference or outcry from the public.
Reduces carbon footprint: processing and distribution of water requires a significant
amount of energy (BlueBarrel, LLC., 2018). The rainwater harvesting system does not require

POTENTIALS OF RAINWATER HARVESTING 22
energy as water is harvested and used on site without processing or distribution. Therefore the
system saves the energy thus reducing pollution and emission of greenhouse gases that are
associated with energy production. Therefore rainwater harvesting system is an environmentally
friendly source of water that helps in protecting the environment.
2.5.2. Disadvantages
High initial cost: the cost of purchasing a rainwater harvesting system and installing it
may be higher than expected. The cost of bigger and more efficient systems is also usually
higher thus the owner will have to spend a significant amount of money so as to install a sizeable
and efficient system.
Maintenance costs: rainwater harvesting systems require continuous maintenance so as to
ensure that they perform efficiently and also to prevent contamination of the harvested water.
The system usually requires frequent checking, including cleaning of the storage tank.
Risk of water contamination: if the rainwater harvesting system is not maintained
properly, the water may get contaminated (Lee, 2015). If this happens, the water will require
treatment before it can be used, which increases the cost. But the risk of contamination can be
prevented through use of the right material and proper maintenance of the system (Amin &
Alazba, 2011).
Limited water storage: the amount of rainwater harvested is limited by the average annual
rainfall received in that particular area. Even if water demand increases drastically, the amount of
rainwater harvested will still remain the same (Rinkesh, 2018). This means that the capacity of
the rainwater harvesting system is largely limited by the amount of rainfall in the area.

POTENTIALS OF RAINWATER HARVESTING 23
Reduces stormwater runoff, flooding and erosion: rainwater harvesting systems are also
useful in reducing occurrences such as flooding, erosion and stormwater runoff (City of San
Diego, 2018). These occurrences usually have devastating effects, including displacement of
people and property destruction.
2.6. Estimation of Harvested Rainwater Volume
Rainwater harvesting potential is dependent on several factors including location, elevation,
roof surface area (size), type of roof, evaporation rake, leakages, etc. The two fundamental
variables that are needed for the calculation of the amount of rainwater that can be harvested
from a rooftop are the rooftop surface area and the average annual rainfall for that specific area.
Since the rainwater cannot be collected 100%, it is recommended to include a collection
efficiency, depending on the type of rainwater harvesting system used. Therefore the estimated
amount of rainwater that can be harvested in Melbourne and Adelaide per m2 of rooftop surface
area is calculated using equation 1 below (assuming a collection efficiency of 90% – 0.9) (Centre
for Ecological Sciences, (n.d.)):
Rainfall harvested per year (m3) = rooftop surface area (m2) x average annual rainfall (m) x
collection efficiency ………….. (1)
Melbourne:
Roof surface area = 1 m2
Average annual rainfall = 666 mm = 0.666 m
Rainfall harvested per year = roof surface area (m2) x average annual rainfall (m) x collection
efficiency

POTENTIALS OF RAINWATER HARVESTING 24
= 1 m2 x 0.666 m x 0.9 = 0.5994 m3
= 599.4 liters of rainwater per year.
Adelaide:
Roof surface area = 1 m2
Average annual rainfall = 536 mm = 0.536 m
Rainfall harvested per year = roof surface area (m2) x average annual rainfall (m) x collection
efficiency
= 1 m2 x 0.536 m x 0.9 = 0.4824 m3
= 482.4 liters of rainwater per year.
The collection efficiency above takes into consideration the efficiency of the rainwater
harvesting system, leaks, absorption and evaporation.
From the above estimations, it shows that Melbourne has a higher potential of rainwater
harvesting than Adelaide. The difference between the rainwater that can be harvested in
Melbourne and Adelaide is 11,700 liters per m2 per year. It is important to note that these
calculations are only used to demonstrate how to estimate the amount of rainwater that can be
harvested in Melbourne and Adelaide. They do not represent the data collected from this study.
The actual data and values to be used in this paper will be obtained from relevant agencies,
departments and other participants specified in the methodology section.
After knowing the amount of rainwater that can be potentially harvested per year, the
next step is to estimate the amount of water usage per household. This can be determined by
looking at the individual household water bills or water meters.

POTENTIALS OF RAINWATER HARVESTING 25
2.7. Water Balance Model
Establishing a balance between water demand/consumption and supply is not easy. This is
due to variable parameters such as amount of rainfall received, population growth and varying
water needs. Water balance models are used to estimate the amount of water supplied and that of
water demanded. This study will create water balance models for Melbourne and Adelaide. The
water balance models will be used to estimate the percentage of water supplied by the rooftop
rainwater harvesting systems in Melbourne and Adelaide, in comparison with the total water
demand in the region. Therefore this model will determine the percentage of water consumption
that is accounted for by the rainwater harvesting systems.
The first water balance models were developed in 1940 by Thornthwaite (Thapa, et al.,
2017). Most of these models were used for water balance analyses and simulating rainfall runoff.
Water balance models are created using the following parameters: rainfall data, rainfall loss
factor, rooftop surface area, rainwater demand, available storage volume and overflow of storage
tank (Imteaz, et al., 2011).
After determining domestic water demand in the two cities, it will be compared with the
volume of potential rooftop rainwater harvested in the two regions. These two sets of data will be
used to create a water balance model. The water balance model is basically used to determine the
gap between water demand and water supply, by taking into account the water demand
(outflow), the volume of rainwater harvested (inflow), and the amount of water remaining
(storage) (Stout, et al., 2017). When the difference between water demand and harvested
rainwater is known, it becomes easy to determine the type and size of rainwater harvesting
systems that can be used to boost water supply.

POTENTIALS OF RAINWATER HARVESTING 26
A water balance model can be used to determine the potential and reliability of rainwater
harvesting systems in an area (Cowden, et al., 2008). In this study, the water balance model will
be used to estimate the percentage of water demand that can be met by the rooftop rainwater
harvesting systems in Melbourne and Adelaide. The model can create a graph showing the
percentage of water demand that is provided by the rooftop rainwater harvesting systems. An
example of such graph is shown in Figure 10 below (Adugna, et al., 2018)
Figure 10: Example of water balance model
From the water balance graph in Figure 10 above, it shows that rooftop rainwater
harvesting systems contribute relatively low percentage of water demand in the study area. In
January, the rainwater harvesting systems accounted for only 0.07% of the total water demand,
in February it was 0.17%, in March it was 0.36%, in April it was 0.57%, in May it was 0.61%, in
June it was 0.90%, in July it was 2.30%, in August it was 2.17%, in September it was 1.02%, in
October it was 0.19%, in November it was 0.10%, and in December it was 0.07%. On average,
the rooftop rainwater harvesting systems account for about 0.71% of the total water consumption
in the area. From this model, it can be concluded that the study area receives high rainfall during

POTENTIALS OF RAINWATER HARVESTING 27
the months of July and August. This model also reveals that most of the water demand in the
area is met by the mains supply. Therefore the potential and reliability of rooftop rainwater
harvesting systems are still low in the area.
Water balance model can be used to establish ways on how to improve the potential of
rainwater harvesting. For example, using graph in Figure 3 above, the volume of rainwater
harvested can be improved by increasing the number and size of rooftop rainwater harvesting
systems. The government can make it mandatory for property owners to install rooftop rainwater
harvesting systems or come up with other strategies of promoting installation of rainwater
harvesting system, such as incentives, tax reliefs, subsidies, etc. Since the amount of rainfall
received in an area cannot be changed because it occurs naturally, the potential of rainwater
harvesting systems can only be improved by increasing the size of rainwater harvesting systems
(size of roof, size of storage tanks, etc.) and the collection efficiency. This requires proper
planning, starting from the design of building roofs that can capture maximum amount of
rainwater.
Water balance models can also be used to determine the months of the year when the
volume of harvested rainwater exceeds water consumption or demand. During these months, the
excess water can be stored in available storage facilities and use later when water demand
exceeds the volume of rainwater harvested by the rainwater harvesting systems.
The water balance model created in this study can be used by the Victoria state
government and the South Australia state government for various projects, such as: improving
the water supply infrastructure (changing the design, establishing the right time for maintenance,
etc.), establishing the right type of rooftop rainwater harvesting systems for the residents,
establish the right approach of water rationing, develop appropriate strategies of preventing

POTENTIALS OF RAINWATER HARVESTING 28
runoff (if needed), etc. The water balance models created in this paper will be very useful in
improving water supply in the two cities by capitalizing on rainwater harvesting systems.
3. Methodology
3.1. Study area
The two cities chosen for the purpose of this study are Melbourne and Adelaide. Both cities will
be studied independently.
3.1.1. Melbourne
Melbourne is the capital city of Victoria state and it is the state’s administrative, business,
recreational and cultural hub. The area of Greater Melbourne area is 9,992.5 km2. The region has
a population of about 4.9 million, with private or residential dwellings approximated to be 1.832
million (City of Melbourne, 2018). The greater area of Melbourne has 23 federal divisions, as
shown in Figure 11 below. The average annual rainfall of Melbourne is 666 mm. There

POTENTIALS OF RAINWATER HARVESTING 29
Figure 11: Federal Divisions of Melbourne
3.1.2. Adelaide
Adelaide is the capital city of South Australia State, with an estimated area of 3,257.7 km2.
The area has a population of about 1.34 million, with private dwellings approximated to be
700,000 (Australian Bureau of Statistics, 2017). The map of Adelaide is as shown in Figure 12
below. The average annual rainfall of Adelaide is 536 mm.
Figure 12: Map of Adelaide
3.2. Google Earth
Recent satellite images of Melbourne and Adelaide will be obtained from Google Earth. The
purpose of obtaining satellite images is to use them for digitalizing the rooftops of all buildings
in these study areas using Google Earth’s polygon tool. To complete the digitalizing process,
building rooftops will be traced directly above the satellite imagery so as to differentiate rooftops
of buildings from other objects in the area. This process will produce digitalized maps of

POTENTIALS OF RAINWATER HARVESTING 30
Melbourne and Adelaide containing thousands of boundaries. The files shall be saved KMZ files
with each file representing building rooftops of Melbourne and Adelaide.
3.3. Calculation of Roof Surface Area
Estimation of the amount of rooftop rainwater that can be harvested is also influenced by the
total surface area of the buildings’ rooftops in the area. Therefore the total rooftop surface area of
buildings in Melbourne and Adelaide will be calculated. Geographical Information System (GIS)
is one of the most important hydrological modelling tools today because of the capacity it has in
handling digital data and information. In this research, ArcGIS’s georeferencing and
digitalization will be used. The process will start by converting the KMZ files for Melbourne and
Adelaide into shape files. This will then be followed by defining the coordinate system for every
shape file so as to enable computation of areas of the digitalized building rooftops. The
calculation of building rooftops surface areas will be done automatically using ArcGIS model’s
geometry calculation tool.
ArcGIS geometry tool has several formulas for calculating area, depending on the shape of
the rooftop. Some of the formulas include the following:
Area of rectangular roof = length x width
Area of circular roof = πr2 (where r = radius of the circular roof).
Area of square roof = side x side
Area of trapezoid roof = 1
2 h(a+b) (where h = height, a and b are the parallel sides of the
trapezoid).

POTENTIALS OF RAINWATER HARVESTING 31
Area of triangular roof = 1
2 bh (where b = base and h = height of the triangle), among others.
3.4. Digitalized Areas Corrections
It is important to confirm the accuracy of the digitalized maps and the subsequent areas using
ArcGIS. To do this, actual areas of a few buildings in Melbourne and Adelaide will be measured
and compared with the corresponding digitalized areas calculated using geometry calculation
tool of ArcGIS. This will be done by selecting five buildings in each of the two cities and
physically measuring the dimensions of their rooftops and using them to calculate the rooftop
surface area. The buildings may be private homes, educational institutions, health facilities,
hotels, offices, etc. The actual calculated rooftop areas will then be compared with the values
obtained from ArcGIS geometry calculation tool. The comparison will then be used to determine
correction factor for each of the selected buildings. The correction factor is simply obtained by
dividing the actual measured area of the building rooftop with the digitalized area.
Area correction factor = Actual measured area
Digitalized area ¿ ArcGIS ¿
The average correction factor will then be calculated from the individual correction factors of the
buildings. This correction factor will be used to modify the digitalized areas. The modified or
corrected areas will be obtained by multiplying the digitalized areas with the average correction
factor.
Corrcted∨modified a r ea=digitalized area x average correction factor
3.5. Estimation of Potential Volumes of Harvested Rainwater
The areas computed using ArcGIS and later corrected by the average correction factor will be
used to estimate the rainwater volumes that can be harvested from the rooftops of buildings in

POTENTIALS OF RAINWATER HARVESTING 32
Melbourne and Adelaide annually using a rational method. The estimation is done using equation
1 provided in introduction section:
Rainfall harvested per year = roof surface area (m2) x average annual rainfall (m) x collection
efficiency
Where values of average annual rainfall in the two cities and collection efficiency are also
needed. The average annual rainfall for the cities will be obtained from meteorological stations.
The calculation of harvested rainwater volumes will be done in Excel.
3.6. Estimation of Water Demand
It is also important to determine the gap between water demand in Melbourne and Adelaide
and the volume of water that can be supplied with rainwater harvesting systems. To achieve this,
water demand in the two cities will be estimated. To start with, the digitalized maps will be used
to identify domestic or residential buildings. It is obvious that water demand for these two
categories is different. Estimating domestic water demand is not that easy considering that every
household has unique water needs and uses the water differently. For example, some households
have water saving plans while others do not have such plans. Also, households use more water
during summer season than winter season. There is also the issue of different number of persons
per household. The water demand in this study will only be domestic water demand.
The domestic water demand will be estimated by considering the number of households in
Melbourne and Adelaide, the number of persons per household, and water demand per person
per day. Alternatively, domestic water demand can be obtained by multiplying the average water
demand per person per day with the total number of people in the city (Biswas & Mandal, 2014).
Since the population of each of these two cities is known, it will be easier to determine domestic

POTENTIALS OF RAINWATER HARVESTING 33
water demand using this alternative. Random sampling will be used to determine the average
water demand per person per day. A total of 50 households will be selected in each of the two
cities then interviews or questionnaires will be used to collect the required data. The main data to
be collected is the amount of water that each household member consumes every day. The
participants will be requested to provide this data by reading water meters directly or obtaining
this information from monthly water bills. In either way, the average water demand per person
shall be obtained by dividing the total monthly volume consumed by the household per month
with the number of household members. The value obtained will then be divided by the number
of days of the month so as to get average daily water demand per person.
Average daily water demand per person= Total olume of water consumed per month
No . of household members x No . of days
To begin with, the number of persons in the two cities (population) will be obtained from
relevant government departments and agencies in the City of Melbourne and the city of
Adelaide. The daily water demand will then be determined from the average values obtained
from 50 households in each city. Total annual domestic water demand will then be determined as
follows:
Total annual domestic water demand = average daily water demand per person x no. of persons
in the city x 365
3.7. Comparing Water Demand and Supply Gap
After determining the water demand, it will be compared with the volume of potential
rainwater harvested in the two regions. This data will then be used to simulate a yearly water
balance model. The model will be created in Excel. One of the limitations of this methodology is

POTENTIALS OF RAINWATER HARVESTING 34
that yearly water balance models are less precise than monthly and daily water balance models
(Wang, et al., 2011).
4. Conclusion
Water scarcity is a problem that is affect many cities across the world. Current issues such as
increasing urban population and climate change are worsening the water crisis problem in cities.
Australia is the driest continent on earth and the fact that most of the Australian cities are
affected by water crisis is not a surprise. One of the approaches that individuals, companies and
governments are using to boost water supply especially in urban areas is use of rainwater
harvesting systems. This paper focuses on the potential of rainwater harvesting systems in
Melbourne and Adelaide. These are two Australian cities with looming water crisis. Rainwater
harvesting systems are an alternative source of water for many cities. The rainwater harvesting
systems can be used in Melbourne and Adelaide to supplement existing water sources, especially
the mains supplies. The rapidly increasing urban population in Melbourne and Adelaide has
greatly stressed mains water supplies hence the need for alternative water sources is inevitable.
The main aim of this study is to investigate the potential of rainwater harvesting systems in
Melbourne and Adelaide. This is so as to establish if these systems can be reliable in alleviating
water scarcity in the two cities by supplementing mains supply. This will be achieved by creating
individual water balance models for Melbourne and Adelaide. The specific objectives of the
study are to evaluate and predict the potential of rainwater harvesting in Melbourne and
Adelaide; to determine the reliability of rainwater harvesting systems in Melbourne and
Adelaide; to assess the effects of Australia’s climatic condition variation on the efficiency and
reliability of rainwater harvesting systems in Melbourne and Adelaide; to assess the amount of
water used in Melbourne and Adelaide and determine if rainwater harvesting systems are a

POTENTIALS OF RAINWATER HARVESTING 35
feasible alternative for water scarcity; and to create a water balance model for the cities of
Melbourne and Adelaide.
The literature review of this paper has discussed various aspects of rainwater harvesting
system including: components of rainwater harvesting systems, functions of rainwater harvesting
systems, advantages and disadvantages of rainwater harvesting systems, types of rainwater
harvesting systems, types of rainwater storage tanks, procedure for estimating harvested
rainwater volume, and the water balance model.
The research will be carried out using a comprehensive methodology that includes the
following aspects: describing the study area, obtaining the maps of study area from Google
Earth, calculating the total roof surface area of residential buildings in the study area using
ArcGIS’s georeferencing and digitalization tools, determining correction factors for the roof area
and using them to correct the digitalized areas, estimating potential volumes of harvested
rainwater, estimating water demand, and determining the gap between water demand and water
supply. All the data and information collected will be used to create a water balance model for
Melbourne and Adelaide.
The average annual rainfall received by Melbourne and Adelaide is 666 mm and 536 mm
respectively. This amount of rainfall is relatively low but it can still be used to harvest some
volumes of rainwater to supplement mains water supplies in the two cities. The water balance
model will determine the percentage of water consumption that is accounted for by the rainwater
harvesting systems. It is expected that rainwater harvesting systems in Melbourne and Adelaide
account for small percentages of water consumption or demand in the two cities. However, the
water balance models created can be used to improve this. Information from water balance

POTENTIALS OF RAINWATER HARVESTING 36
models is useful in establishing ways of improving the potential, efficiency and reliability of
rainwater harvesting systems.
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