Rainwater Harvesting in Sydney, Australia

This research explores rainwater harvesting as a solution to water scarcity in Sydney, Australia. It discusses the background of water scarcity, the concept of rainwater harvesting, and the rationale for conducting this research. The study aims to analyze the feasibility and reliability of rainwater harvesting in Sydney, determine the optimum design of rainwater harvesting systems, and estimate the amount of rainwater that can be collected. It also examines the trend of climate variability and water demand in the Greater Sydney region. The research objectives include investigating water collection using e-Tank, a daily water balance model, and determining the payback period of rainwater harvesting systems in Sydney.

Rainwater Harvesting in Sydney, Australia 1
RAINWATER HARVESTING IN SYDNEY, AUSTRALIA
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Rainwater Harvesting in Sydney, Australia 2
Table of Contents
1. INTRODUCTION.............................................................................................................................3
1.1. Background................................................................................................................................3
1.2. Rainwater Harvesting................................................................................................................4
1.3. Research Rationale....................................................................................................................5
1.4. Research Objectives...................................................................................................................8
2. LITERATURE REVIEW.................................................................................................................8
2.1. Water Sustainability..................................................................................................................8
2.2. Advantages of Rainwater Harvesting.....................................................................................11
2.3. Disadvantages of Rainwater Harvesting................................................................................13
2.4. Factors Affecting Adoption of RWHS....................................................................................15
2.5. Design of RWHS......................................................................................................................17
2.6. Rainwater Harvesting in Different Global Cities..................................................................20
2.7. RWHS Research in Australia.................................................................................................25
2.8. RWHS Research in Sydney.....................................................................................................28
2.9. Description of Study Area.......................................................................................................33
2.10. Climate of Sydney................................................................................................................34
2.11. Daily water balance model – e-Tank..................................................................................35
References................................................................................................................................................37

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1. INTRODUCTION
1.1. Background
Water scarcity is one of the major problems facing the world today (Kummu, et al., 2016);
(Srinivasan, et al., 2012), despite the fact that water is a very essential commodity for human,
plant and animal life (Reid, 2019). Even though about 70% of the surface of the earth is covered
with water, only around 3% is freshwater suitable for human consumption. Approximately 1.1
billion in different parts of the world do not have access to water (Rinkesh, (n.d.)). The water is
mainly sourced from groundwater (wells, boreholes and springs), surface water (rivers, lakes,
oceans and streams) and rainwater (Adugna, et al., 2018). The water scarcity problem is affecting
all aspects of human life, including social, economic, environmental and political aspects
(Stuckenberg & Contento, 2018). There are several factors contributing to this problem
including: rapid global population growth, increased industrialization and urbanization, overuse
and/or misuse of water, pollution of water, conflict, global warming and climate change. Water
demand has been increasing gradually over the past decades and is predicted to continue
increasing while water availability and supply are continuing to decrease (Harhay, 2011). As this
imbalance continues to widen, the lives of present and future generations are being threatened
even more. By 2025, water scarcity is anticipated to become a global crisis
(TheWaterGeeks.com, 2019). Water scarcity problem is a major concern in Australia because
this is the driest continent on earth that is inhabited by human beings (Sawe, 2018). Australia is
the continent that has the lowest volume of water in rivers, least permanent wetlands area and
lowest runoff (Australian Government, 2019).
The increasing water scarcity in Australia and other regions across the world is a
sufficient reason to carry out and support studies aimed at finding reliable and sustainable

Rainwater Harvesting in Sydney, Australia 4
solutions to water scarcity problem. This research is aimed at analyzing rainwater harvesting as a
solution to help increase water availability and supply in Sydney.
1.2. Rainwater Harvesting
Several studies have found that rainwater is the most economical, environmentally friendly and
sustainable alternative source of water (Bashar, et al., 2018); (Tamaddun, et al., 2018). The
rainwater can be collected using a rainwater harvesting system (RWHS) (Che-Ani, et al., 2009).
This is a system that has been designed to collect and storage rainwater for future use (Hari, et
al., 2018). There are two main types of RWHS: domestic RWHS and agricultural RWHS. The
domestic RWHS uses rooftops of buildings as the catchment area and water tanks as storage
systems for the collected rainwater. On the other hand, agricultural RWHS uses land as the
catchment area and stores the collected rainwater in ponds (Rozaki, et al., 2017). This research
focuses on domestic RWHS.
There are also different types of domestic RWHS but the typical RWHS comprises of the
following components: catchment and conveyance system, filtration system, water storage tank,
treatment system, pumping system, and other fixtures (such as overflow). The catchment and
conveyance system comprises of the building roof, gutter and downpipe/downspout. The
function of this system is to collect the water falling in form of rain and direct it to the filtration
and storage tank. The filtration system is used to sieve the collected water so as to get rid of large
particles. Another system used in place of the filtration system is first flush diverting device. The
storage tank, as the name suggests, is used for storing the collected rainwater. The treatment
system is optional because some RWHS do not have it. The main function of this system is to
purify water so as to make it potable. Inclusion of the treatment system depends on the intended
use of the water and the financial capability of the building owner. The pumping system is used

Rainwater Harvesting in Sydney, Australia 5
for impelling and transporting rainwater from the storage tank to the final place of use. The
overflow is a device used for discharging the excess rainwater in the storage tank into the sewer
system. Figure 1 below shows a typical RWHS.
Figure 1: A typical RWHS (Water Rhapsody, 2015)
The collected rainwater can be used for irrigation, indoor uses and whole house uses.
Some of the specific uses of rainwater include: irrigating the gardens; washing vehicles, pets,
walkways or driveways and utensils; refilling the swimming pool, fish ponds and fountains;
flushing toilets; washing clothes; and other potable needs (if the rainwater is property filtered and
treated).
1.3. Research Rationale
Sydney is a coastal town and is the most populous and one of the largest cities of Australia. The
city has continued to develop and has recorded a significant population growth over the past
years. This development and population growth have also increased the city’s water demand.
About 80% of drinking water in Sydney is sourced from Warragamba Dam. It means that the
main source of municipal water in Sydney is surface water. This makes water supply in Sydney

Rainwater Harvesting in Sydney, Australia 6
highly susceptible to drought. For example, the levels of Warragamba Dam have fallen below
60% due to drought, climate change and other human activities. This exposes Sydney to high
risks of water scarcity. There have been proposals to increase the height of Warragamba Dam by
14 meters but this proposal has attracted a lot of controversy. The reason for this controversy is
because the suggested elevated dam is located in Blue Mountains national park, which is on the
world heritage list, and therefore it would cost a lot of money and affect environmentally
sensitive ecosystems and Aboriginal cultural heritage (Salbe, 2019). It has also been reported
that water flows into the drinking catchment area of Sydney are at a record low, raising more
concern about water security of the city (McGowan, 2018).
Mayors of several councils in western NSW have already raised their concerns about the
looming water shortage crisis (Davies, 2019). According to experts, supply of freshwater in
Sydney and other cities across Australia is increasingly susceptible to drought that is caused by
climate change. As a result, the need to look for alternative sources of water and adopt water
conservation strategies cannot be overemphasized. One of the suggestions made by the
Australian government and other state governments is construction of desalination plants.
However, this proposal takes longer to be implemented and requires a lot of money. Considering
the location and climate of Sydney, rainwater harvesting is a feasible solution that can help
reduce the risks and impacts of water scarcity in the city. As a way of addressing the water
sustainability concern, both the federal and state governments have formulated regulations and
created incentives to promote adoption of RWHS. The applicable regulation for Sydney is the
NSW Health Guidelines of 2015 that competed the Building Sustainability Index (BASIX). One
of the main requirements of BSI is that all new residential buildings in NSW must be designed to
use less municipal water. The reduction target for Sydney is 40% meaning that new residential

Rainwater Harvesting in Sydney, Australia 7
buildings in Sydney should be designed to minimize normal water consumption by at least 40%
(National Poly Industries, 2018). The major proposal of achieving this target is to install RWHS
(Chubaka, et al., 2018).
Many residents in Sydney and other parts of Australia are aware of the water
sustainability challenge and have embraced the idea of RWHS. According to Australian Bureau
of Statistics (ABS), 26% or one in four Australian houses have at least one rainwater tank.
However, majority of people do not have proper understanding of the most suitable size of
RWHS that will meet their water demand. This is mainly because of lack of adequate studies
about appropriate sizing of rainwater tanks with consideration of factors such as the location,
cost and reliability of the rainwater storage tanks. Majority of the studies that have been
conducted on rainwater harvesting in Sydney have also used historical data of daily water
consumption and rainfall. This historical data has been simulated to determine average data for
use in the studies of RWHS in Sydney. Use of historical data may not provide accurate results of
the right size of rainwater tanks for residents in Sydney because it does not depict the actual
current scenario. Factors such as climate change and lifestyle changes have made use of
historical data less accurate when determining the right type and size of RWHS. For instance,
weather patterns are nowadays unpredictable and people’s lifestyles are continuously changing.
These two main factors have significant impacts on the water availability and demand because
they affect rainfall variability and water consumption. For instance, droughts that have become
common in Australia means less rainfall and high water consumption and evaporation that
reduces water availability. This makes it necessary to collect actual data of rainfall received and
water consumption in Sydney so as to get more accurate and realistic results that will help in
determining the most appropriate type and size of RWHS for Sydney residents.

Rainwater Harvesting in Sydney, Australia 8
The initiative of collecting actual data reduces the likelihood of under-designing or
overdesigning RWHS. This is very important because using data that depict the real scenario
means that the RWHS install will adequately meet the water needs of the user. Therefore this
study aims at improving the previous studies by overcoming their main shortcoming of using
historical data to determine the optimum design of RWHS. The kind of rainfall variability and
lifestyle and water usage patterns experienced in Sydney requires use of data that represent the
actual scenario so as to determine the optimum size of RWHS for use in boosting water supply
and availability in Sydney.
1.4. Research Objectives
The following are the main objectives of this research:
 To investigate the trend of climate variability and water demand in the Greater Sydney
region.
 To estimate the amount of rainwater that can be collected in Sydney using rooftop
RWHS.
 To analyze the feasibility and reliability of using RWHS in Sydney.
 To analyze water collection by RWHS using e-Tank – a daily water balance model.
 To determine the optimum design of RWHS in Sydney.
 To determine the payback period of a RWHS in Sydney.
2. LITERATURE REVIEW
2.1. Water Sustainability
Water scarcity is a serious global problem and the current water demand has by far surpassed the
capacity of conventional water sources (Keskar, et al., 2016). As aforementioned, Australia is the

Rainwater Harvesting in Sydney, Australia 9
inhabited continent that is driest on earth and it is also the continent that experiences the largest
extent of variable rainfall. These two factors have made Australia to be greatly affected by
drought (Apostolidis, et al., 2011). Achieving water sustainability is a serious challenge not only
in Australia but in all parts of the world. The increasing human population, urbanization,
industrialization and current global climate change have put great pressure on the existing water
sources and supply systems. The real scenario is that water demand is increasing rapidly while
water availability and supply is decreasing with the same rate. This has contributed to expanding
gap between demand and supply of water in many cities across the world (Sharma, et al., 2016).
Rainwater harvesting is unarguably one of the most suitable long term solutions to achieving
water sustainability. This is because rainwater is a free natural resource and RWHS has almost
zero negative environmental impacts.
Rainwater harvesting is not new but has been in use for thousands of years all over the
world (Bitterman, et al., 2016). Use of RWHS is prevalent in Australia, Germany, U.S., China,
Japan and India. With the current trend of rapid population growth, the need for increased use of
RWHS cannot be overemphasized. As stated above, this is because water demand is increasing at
a very high rate and the municipal water supply systems are under great pressure (Shukla, et al.,
2013). There are many countries that have already formulated policies to promote adoption of
RWHS. For example, about 74% of homes in Germany have a RWHS and all new structures
with an area of more than 400 square feet are required by law to have a RWHS. In Australia,
close to 100% of homes have a RWHS. In Texas, U.S., all new government buildings must have
a RWHS and the RWHS are sold tax free (Bond, (n.d.)). All these initiatives are aimed at
improving water sustainability.

Rainwater Harvesting in Sydney, Australia 10
Water is a free natural resource that can be harvested easily using cost effective methods
such as RWHS (Mwamila, et al., 2016). Increasing urban population has resulted to increased
demand for municipal water supply in many cities. A study carried out by Rahman, et al. (2014)
revealed that RWHS is the most conventional and sustainable approach that can be used to
provide water for potable and non-potable uses in commercial and residential buildings in almost
any city across the world. This could significantly minimize the current pressure on supply on
processed water thus improving sustainability. In this study, the researchers investigated the
sustainability of RWHS by examining various parameters of rainwater including the water pH,
total dissolved solids (TDS), fecal coliform, turbidity, lead, BOD5, total coliform, and NH3-N,
among others. They found that the overall quality of rainwater collected using RWHS was within
the water quality standards and/or requirements of Bangladesh. Another finding from the study
was that RWHS can provide adequate volume of water needed by a small to medium size
household and energy savings. The system is also economical and effective considering the
installation and maintenance costs. They concluded that RWHS was a feasible, financially viable
and sustainable alternative source of water in Dhaka City, Bangladesh.
There are different ways in which RWHS contributes to the overall sustainability of
water. First and foremost, rainwater harvesting reduces the consumption of water from the
municipal water supply or it generally minimizes the demand for processed water. This means
that less water will be extracted from sources such as dams, rivers, seas and oceans. The end
result is conservation of water in these traditional water sources, which enhances water
sustainability because the conserved water can be used during drought seasons. RWHS also
enhances water sustainability by saving energy that could be used in extraction, processing,
transportation and pumping of water. A large percentage of this energy is generated from non-

Rainwater Harvesting in Sydney, Australia 11
renewable sources that have devastating effects on the environment, including water sources. It
therefore means that RWHS saves energy and minimizes the negative impacts on water sources.
Last but not least, RWHS improves water sustainability by encourages people to develop
appropriate water usage behaviours. People who have invested in RWHS tend to be more
vigilant on how they use water because they want to minimize wastage so as to significantly
reduce water bills. In the process, they end up meeting most of their water needs from the
rainwater. This reduces the pressure on the conventional water sources thus enhancing water
sustainability (Pachpute, et al., 2009). The overall sustainability of RWHS can also be increased
through the financial, administrative, regulatory and technical support of the government and
other relevant stakeholders (Jha, et al., 2019).
2.2. Advantages of Rainwater Harvesting
Rainwater harvesting has numerous economic, environmental and social benefits. Some of these
benefits include the following:
Free and clean water: rainwater is available for free and it is very clean. This means that
the water can be collected any time it rains and used directly without purification (for uses such
as washing and irrigating gardens).
Reduces water bills: use of RWHS significantly reduces the amount of water needed
from the supply company or municipal water. This means that the utilities bill also reduces. If
used on an industrial scale, RWHS can provide water needed for most of the industrial
operations thus reducing water bills for the company.
Numerous uses: rainwater is suitable for numerous uses, such as cleaning, washing,
watering gardens (Chao-Hsien, et al., 2014), and flushing toilets. If this water is treated or

Rainwater Harvesting in Sydney, Australia 12
purified, it can also be used for bathing, cooking and drinking. This means that the rainwater can
be used for both potable and non-potable purposes.
Control of water supply: rainwater harvesting enables the building owner to have total
control over water supply to the building. With a RWHS, water will be available even when the
water companies are rationing this important commodity. This makes RWHS very useful in
cities with water rationing.
Socially acceptable: RWHS have been in use for many years and they are acceptable all
over the world. It is important to note that there are different types and designs of RWHS. Some
of these systems are very simple and do not contain all the components discussed above. For
example, a RWHS can only comprise of a gutter and a portable storage tank. This kind of RWHS
is very common in rural areas in underdeveloped or developing countries.
Environmentally friendly: collection, storage and use of rainwater do not have any
negative impacts on the environment. RWHS significantly reduces the environmental impacts
associated with the mechanized extraction, processing and transportation of water.
Water conservation: use of rainwater reduces the need to collect water from other natural
sources such as rivers, lakes and seas. This means that use of RWHS is one way of conserving
the natural resource of water because it minimizes depletion of water from nearby sources.
Reduces floods: when it rains heavily, many areas experience floods. This problem can
be prevented by installing RWHS on all buildings. Doing so will ensure that the largest
percentage of rainwater is collected and stored, leaving a very small percentage that cannot cause
floods.

Rainwater Harvesting in Sydney, Australia 13
Reduces soil erosion: similar to reducing floods, rainwater harvesting also minimizes soil
erosion. This is because most of the rainwater is harvested and the remaining runoff is not
adequate to wash away the top soil when it rains.
Minimizes groundwater demand: increasing water demand and water scarcity have
resulted to excessive extraction of groundwater. This has resulted to depletion of groundwater
and caused groundwater levels to go very low. As a result, drilling water is these areas becomes
problematic and the ecosystem also gets affected.
Simplicity: RWHS is based on a very simple technology. Installation of the simplest form
of RWHS can be done by anybody without necessarily having the specialized or professional
knowledge and skills of installing the RWHS. The RWHS can also be easily installed on new or
existing buildings.
Low maintenance costs: RWHS have very low maintenance needs and costs. Once the
system is installed, it can last for many years without requiring substantial maintenance works.
Maintenance of RWHS also requires little energy and time.
Save lives: as stated before, water scarcity is a life threatening problem. Many people die
every year due to lack of access to water or water related problems such as waterborne diseases.
Rainwater harvesting can increase water availability and supply thus preventing these problems
and their associated deaths.
2.3. Disadvantages of Rainwater Harvesting
Despite the numerous advantages of RWHS, rainwater harvesting also has some disadvantages.
Some of these disadvantages include the following:

Rainwater Harvesting in Sydney, Australia 14
Unpredictable rainfall: it is rather obvious that rainfall cannot be accurately predicted.
This is even worse nowadays sue to fluctuating weather patterns caused by climate change.
Many parts of the world also experience rainfall for only a short period throughout the year. This
means that people cannot only rely on RWHS for all their water needs because they can lack
rainfall for several months. Therefore it is advisable not to depend on rainwater only. RWHS are
most suitable in areas that receive plenty of rainfall evenly distributed throughout the year.
High initial capital: the cost of installing a RWHS varies depending on the type, size and
location. The average cost of installing an efficient RWHS that has the capacity to supply
adequate water for domestic use is $9,000, but the lowest cost is about $2,000. However, some
simpler RWHS can cost as low as $200. In general, the initial cost of a good RWHS is relatively
high and many people who are in dire need of clean water, such as those in underdeveloped
countries, cannot afford it. The estimated payback period of RWHS is 10-15 years.
Storage limits: the amount of rainwater than can collected and stored also depends on the
size of the storage tank. This means that even if it rains heavily, the rainwater that can be held is
only equivalent to the size of the storage tank. All other excess water will go to waste.
Toxic roof particles: some roofs are made of chemicals that can affect the quality of
rainwater. When it rains, these roof chemicals reacts and mixes with water. The rainwater
collected will then be toxic for use and must be treated first, which increases the cost and
neutralizes the benefit of reducing water bills. Therefore it is important to ensure that the
building roofs are made of non-toxic materials or the water must be treated if it is intended for
potable use (Gikas & Tsihrintzis, 2017).

Rainwater Harvesting in Sydney, Australia 15
Regular maintenance: RWHS requires regular maintenance to prevent deterioration of
rainwater collected. The RWHS are usually prone to algae growth, rodents, lizards, mosquitos
and other insects. All these can damage the system or affect the quality of rainwater collected
making it unsuitable for use.
2.4. Factors Affecting Adoption of RWHS
It is evident that RWHS can significantly help in saving water and solving the problem of water
scarcity in many parts of the world. Nevertheless, the potential of RWHS has not been fully
exploited. This is due to several factors that are inhibiting adoption of RWHS. Some of these
factors are as follows:
Frequent flooding: some parts of the world are experiencing frequent flooding caused by
climate change. These floods have created the impression that there is no need of harvesting and
storing rainfall because it is going to continue raining heavily within a shorter time interval thus
water will be available in abundance. This is usually not the case because weather patterns are
continuing to be unpredictable and areas that are experiencing frequent floods may start
experiencing severe drought in the near future. The best solution to this problem is to have a
RWHS so as to harvest rainfall whenever it rains and store the rainwater for future use.
Low water tariffs: this is another major factor contributing to slow adoption of RWHS.
Water tariffs in some parts of the world, especially those that receive adequate or excess rainfall
throughout the year, are very low. This makes it uneconomical to install RWHS because of the
easy and cheap availability and supply of water.
Lack of government incentives: incentives play a very key role in promoting adoption of
relatively new technologies such as RWHS. Provision of government incentives, especially

Rainwater Harvesting in Sydney, Australia 16
economic incentives, is a way of government motivating and showing its commitment in
promoting the subject matter, product or technology. Examples of incentives are: tax abatement,
tax credit, low interest financing, infrastructure assistance, grants, subsidies, and free
professional consultancy services. The main function of incentives is to reduce the cost and
enhance the ease of installing, operating and maintain RWHS. Lack of incentives makes the cost
of installing RWHS to remain high and unattainable for many households. Therefore the
government can encourage more people to install and use RWHS by providing incentives
(Rahman, et al., 2012). If incentives are provided, many people and companies will be motivated
to include RWHS when designing their homes or business premises. (Rahman, et al., 2014)
Lack of a proper regulatory framework: adoption of RWHS can only be increased if
proper policies are formulated to promote and enforce RWHS (Fewkes, 2012). This requires
relevant government agencies and departments to formulate appropriate policies that are aimed at
promoting adoption of RWHS. One of the strategies that can be used is to formulate a policy
making it mandatory for new buildings to have a RWHS. This means that a planning permit or
building permit for new buildings will only be issued if the building design has incorporated a
RWHS. This kind of policy can ensure that 100% of homes in a country or region have RWHS.
Hence it is the responsibility of the government to ensure that they formulate policies and create
a regulatory framework that promotes adoption of RWHS.
Lack of awareness: there are also many people who are not aware of the various types,
designs and sizes of RWHS, and benefits and drawbacks of these systems (Akroush, et al.,
2016). Such people do not have adequate knowledge on the cost-benefits of RWHS and how
they can save money and protect the environment through use of RWHS. This means that
adoption of RWHS can be increased by conducting awareness campaigns so as to educate more

Rainwater Harvesting in Sydney, Australia 17
people about these systems and their benefits (Dismas, et al., 2018). As a matter of fact, there are
some people who believe that RWHS are very expensive, not knowing that the cost depends on
factors such as design and size of the system and the location. Additionally, such people are not
aware that the cost of RWHS can be reduced further by taking advantage of the available
government or economic incentives. Therefore the level of education also plays a part in
promoting or inhibiting adoption of RWHS. People with a higher level of education are more
likely to support adoption of RWHS than those with a lower level of education (Aziz & Tesfaye,
2013).
Cost: the average cost of installing a modern and efficient RWHS that is able to supply
all the water needs of a household or company operations is $9,000. This cost is relatively high
and cannot be met by households especially in underdeveloped and some of the developing
countries. The income levels of residents in these countries are very low and their monthly
income is irregular (Staddon, et al., 208). As a result, investing this kind of money in RWHS is
not reasonable. On the other hand, households with more are likely to adopt RWHS because they
are not constrained financially hence can bear risks associated with installation of new RWHS
(Mekonnen, 2017). One strategy that can be used to overcome this challenge is for the
government to partner with other private and non-government organizations so as to reduce the
cost of instating RWHS by providing incentives or other free products and services that will
lower the cost of RWHS.
2.5. Design of RWHS
The size of a rainwater storage tank plays a key role in achieving the objectives of installing a
RWHS (Aurib, et al., 2017). The storage tank is the most expensive component of the RWHS
and therefore it should be chosen intelligently and with justification using simulations and

Rainwater Harvesting in Sydney, Australia 18
calculations. Khan, et al. (2017) conducted a study on the best approach of determining the
optimum size of storage tank. In this study, they used a simulation model to develop a user-
friendly software that could be used to estimate the optimum size of rainwater storage tank and
reliability of the RWHS by considering variables such as the location, water demand, types of
materials and catchment area. They used a 24-year period rainfall data collected from the
Bangladesh Meteorological Department for various regions of Bangladesh. The researchers
developed the program using the concept of yield after spillage meaning that they calculated the
net volume of rainwater collected by the RWHS. Key parameters calculated from the study were
volumetric variability and time variability. It was found from the study that the program created
was able to determine the optimum size an efficiency of rainwater storage tank for combination
of different variables. They used the software to assess RWHS in Khulna (a coastal area),
Rajshahi (an area with low precipitation) and Comilla (an area affected by arsenic). This study
demonstrated the importance of collecting data that depicts the real situation of the case study
area. That is why the optimum rainwater storage tank sizes, volumetric reliability and time
reliability were different for each of the areas assessed.
The optimum size of RWHS is influenced by several factors including: rainfall intensity
or potential in the area, size of catchment or roof surface area, type of roof, and water demand
(which can be influenced by the number of persons in the household) (Allen & Haarhoff, 2015);
(Tsihrintzis & Baltas, 2014). The first step is to calculate the amount of rainwater that can be
collected using the RWHS either annually, monthly or daily. The annual, monthly or daily
rainfall data can be obtained from historical records maintained by the relevant meteorological
agencies or measured by the researcher over a certain period of time. It is recommended to use
the latest rainfall data available so as to get close to real situation because weather patterns have

Rainwater Harvesting in Sydney, Australia 19
been greatly fluctuating over the past few decades. The optimum rainwater storage tank size
must be determined for the RWHS to achieve the highest reliability and efficiency levels (Khan,
et al., 2017).
The maximum amount of rainwater that can be collected from the RWHS can be
estimated by multiplying average annual rainfall by the roof area and runoff coefficient (Shittu,
et al., 2012). The runoff coefficient is dependent on the type of roof material because each
material has a different water absorption capacity. The runoff coefficient for various types of
roof materials are provided in Table 1 below (Kumar, 2015). Water usage can be determined
from monthly water bills of a specific building or reading directly from the water meter of the
building over a certain period of time. The volume of daily runoff is calculated by multiplying
the contributing roof area with the daily rainfall amount. The volume obtained is then adjusted
by subtracting losses due to spilling, leakage and evaporation. These losses are taken as 15% of
the daily runoff volume. The water usage should be based on the dry season – the number of
days between two consecutive rainy seasons in the area of study. The family water requirement
for the dry season can be determined by multiplying the number of days by the size of the family
(number of family members) and the estimated daily water consumption per person. The
optimum size of the rainwater storage tank can then be estimated by multiplying the family water
requirement by a factor of safety (which can be taken to be 1.2).
Table 1: Runoff coefficients
Type of roof material Runoff coefficient
Thatched or organic 0.2
Flat cemented roof 0.6-0.7
Glazed or tiles 0.6-0.9

Rainwater Harvesting in Sydney, Australia 20
Aluminium sheets 0.8-0.9
Well-constructed roof 0.9
Galvanized iron sheets >0.9
2.6. Rainwater Harvesting in Different Global Cities
Rainwater harvesting is an alternative source of water that is used in almost all parts of the
world. The continuing urban population growth and unpredictable weather patterns due to
climate change have made RWHS more prevalent in global cities. Even the state and local
governments are doing everything possible to promote adoption of RWHS because they know
that they cannot meet the increasing water demand. The RWHS can be a reliable source of water
if it is designed, operated and maintained properly. Proper design means selecting the optimum
type and size of RWHS using statistical, analytical and simulation tools, and ensuring that it is
installed by a trained installer. Proper operation means that means that the daily water extracted
from the rainwater storage tank is within the design or acceptable limits. Proper maintenance
means that the RWHS is inspected regularly to make any necessary repairs, identify faults and
rectify them before they affect the efficiency and effectiveness of the system.
Zavala, et al. (2018) carried out a research to determine the reliability of using rainwater
harvesting system to meet the water demand of a Mexico City-based transportation logistics
company. The researchers determined water usage in the company’s buildings and facilities and
also used statistical rainfall analysis to estimate the amount of rainwater that could be collected
from the maneuvering yard and roofs. It was found from the study that rainwater could meet the
company’s total water demand. They also found that it was more economical to install a RWHS

Rainwater Harvesting in Sydney, Australia 21
integrated with a water treatment system instead of collecting the rainwater and treating it
separately. The analysis showed that the RWHS will help the company generate substantial
economic benefits and their investment will be amortized within a period of five years only. The
net present value (NPV) of the RWHS will be $5,048.3, the benefits-investment ratio (B/I) will
be 1.9 and the internal rate of return (IRR) will be 5.7%. From this study, it is evident that
RWHS is financially viable if it is planned and implemented diligently. In case the rainwater
collected is intended for potable use, the RWHS should have an integrated treatment system so
as to purify water on site instead of transporting it to a different offsite water treatment facility.
This will obviously reduce the cost and environmental impacts associated with the transportation
and treatment of rainwater offsite.
Matos, et al. (2013) investigated the sizing of rainwater storage tank for a commercial
building (Dolce Vita Braga) in Braga, Portugal. The main purpose of the study was to determine
the most suitable RWHS configuration for the three storey building considering three different
scenarios of non-potable water uses (toilet flushing, pavement washing and irrigation). The total
roof area of the building was 36,870 m2 and the total consumption of the three non-potable water
uses was 6,408.19 m3 per month. The researchers used Rile method and 88% efficiency criteria
for sizing the RWHS for the building. Different scenarios of non-portable water uses were
studied so as to determine the best solution. After conducting comprehensive analysis of various
scenarios, they concluded that the most reasonable solution for the building was where rainwater
collected would be used for pavement washing and irrigation. The rainwater storage tank
volumes of other scenarios were very large and seemed not to be feasible considering the
location, construction, costs and payback period. The storage volume of the selected scenario

Rainwater Harvesting in Sydney, Australia 22
was 11 m3, which is still high but reasonable considering the size of the building and the water
consumption.
Results obtained from this study showed that the accuracy of the criteria used in sizing
the RWHS is very critical. Some of the sizing criteria can give unreasonable rainwater storage
tank volumes or sizes. In this case, the results obtained from the Ripple method were
unreasonable and it was due to the deficiencies of this method, which include sampling errors of
the observed data and very small reservoir capacities produced from the coarse time
discretization. It was concluded from the study that another method or water balance model
should be used to as to determine more accurate results of sizing the RWHS. The study should
also include analysis of installation costs of the proposed RWHS. Nevertheless, the study
revealed that the large roof area of commercial buildings can be used to collected adequate
rainwater for use in onsite irrigation and pavement washing. Another key finding from the study
was that it is recommended to use daily water consumption rather than monthly or annual water
consumption when investing RWHS sizing.
Several studies have also been conducted to investigate the feasibility of using RWHS in
water scarce regions. One of such studies was conducted by Patel & Shah (2015), to determine
the applicability and suitability of RWHS in North Gujarat, a region in northern part of India
where the average rainfall received is below normal average. In this region, the main source of
water was underground water and it had been continuously declining. The aim of the study was
to determine the most affordable technologies that could be used to collect rainwater from roads
and rooftops so as to increase water supply and reduce pressure on the depleting groundwater
source. The specific area of study was Amba Township, located approximately 10 km from
Gandhinagar, North Gujarat. The area did not have a reliable source of water other than

Rainwater Harvesting in Sydney, Australia 23
groundwater. The total area of study was 44,022 m2, total building rooftops was 22,011 m2, the
average annual rainfall was 740.3 mm and the population was 1,000. Calculations showed that
the annual total water demand for Amba Township was 49.275 x 106 liters and the annual total
rainwater that could be harvested was about 14.63 x 106 liters, accounting for approximately
30% of the annual total water demand. The main finding from this study was that RWHS are
applicable even in areas that receive below average rainfall. The rainwater can be harvested and
used to recharge the ground aquifer thus reducing depletion of groundwater.
A similar study to the one above is that conducted by Taffere, et al. (2016), who sought to
establish the reliability of existing traditional RWHS in Mekelle, a city in Ethiopia, sub-Saharan
Africa. The city is located in a semi-arid region and RWHS is one of the alternative sources of
water aimed at curbing the water scarcity problem. The average annual rainfall in the region was
755.8 mm and the study population was 12,281. A total of 67 RWHS installed in the city were
analyzed and only 32 were found to be functional. The study found that the unreliability of the
existing RWHS was very high (about 91% of the RWHS were unreliable for water supply).
68.7% of the RWHS had low reliability, 28.1% had medium reliability and 3.1% had high
reliability.
The overall low reliability was attributed to the fact that the design of the system was
inefficient. The existing traditional RWHS was designed without considering the essential
factors such as the average annual rainfall in the region, total water demand, rooftop area, family
size and size of the rainwater storage tank. The assumed values of daily water demand per
household per day, family size and storage capacity were very low compared to the real values.
Roof area has a very essential impact on the reliability of the RWHS. Households with larger
roof areas recorded higher reliability while those with smaller roof areas recorded low reliability.

Rainwater Harvesting in Sydney, Australia 24
The size of roof area determines the amount of rainwater that can be collected. It was concluded
that the reliability of RWHS can be increased by increasing the roof area so as to collect more
rainwater during the dry season or increasing the storage tank size so as to store more surplus
rainwater during the rainy season so as to be used during the next dry season.
A reliability analysis of RWHS in southern Italy was carried out by Notaro, et al. (2016)
in southern Italy. The study emphasized on using RWHS as an effective alternative source of
water to solve the current problem of water scarcity being experienced in the Mediterranean
region. The case study was use of RWHS to supply water for flushing toilets in a single-family
residential dwelling located in Sicily, southern Italy. The flushing water demand pattern was
determined using historical water consumption data. They performed the rainwater storage tank’s
water balance simulation and evaluated the performance of the model. The main finding from the
study was that RWHS can provide more economic and environmental advantages if used in
Sicily than conventional water supply methods. However, a catchment area of between 200m2
and 300m2 is required for the RWHS to achieve good performance. With the application of
RWHS in Sicily, it is possible to achieve up to 85% in water saving efficiency.
Many of the above studies have focused on the economic and social benefits of RWHS.
Another important aspect of RWHS is their environmental benefits. A study by Teston, et al.
(2018), revealed that RWHS also plays a key role in preventing negative environmental impacts
associated with heavy downpour. The researchers conducted the study to investigate the impact
of using rainwater for consumption by single-family houses and the impact of RWHS on
drainage systems. The houses investigated were located in Curitiba, a city in southern Brazil.
The sizing of rainwater storage tanks was done using two different methods then the efficiency
and reliability of existing RWHS were verified. It was found that the two rainwater storage tanks

Rainwater Harvesting in Sydney, Australia 25
analyzed had a reliability of at least 80% and they reduced the peak flows by 4.4% and 4.9%
respectively. The reliability was directly proportional to the size of the storage tank, which is a
similar finding from other studies. In general, the study found that RWHS significantly reduces
runoff that would have to be treated first before being released into receiving water bodies.
Besides reducing reliance on municipal water supply, the RWHS can also be used to regulate the
amount of runoff discharged into drainage systems.
The literatures above show that RWHS is applicable and has been proven to be an
efficient and reliable alternative source of water in all parts of the world, including urban and
rural areas. It is true that many cities have turned to RWHS as a way of increasing water supply
for various uses in homes and businesses. Nevertheless, the percentage of reliability of RWHS
depends on various factors including design parameters, installation, operation and maintenance
of the RWHS. If the RWHS is designed by considering the accurate values of water demand,
family size, rainfall and storage tank size, chances of achieving greater reliability are very high.
The reliability and efficiency of RWHS are also dependent on the specific location or scenario
where the system is used. This is because each scenario has unique population size (such as
number of family members), water demand or consumption per day, rainfall amount and storage
tank size. This makes it necessary to investigate the applicability, reliability and sustainability of
RWHS in Sydney. Findings from such a study can help relevant stakeholders to formulate
policies or regulations that will promote adoption of RWHS in Sydney and help the city
overcome the water scarcity problem.
2.7. RWHS Research in Australia
The climate of Australia is very variable and the continent features different climatic
zones (Keywood, et al., 2016). There are large seasonal variations in both temperature and

Rainwater Harvesting in Sydney, Australia 26
rainfall. The continent also experiences a wide range of nature’s extreme weather events such as
floods, drought, severe storms, tropical cyclones and bushfires, among others. About 80% and
50% of Australia’s land receives less than 600mm and 300 mm of average annual rainfall,
respectively (Australian Bureau ogf Statistics, 2015). The climatic conditions variations and
water scarcity have made rainwater a popular alternative source of water in Australia. Most of
the households in Australia have and use a rainwater tank and the percentage of the households
with rainwater tanks has continue to increase over the years. The number of households with
rainwater tanks in capital cities was less (28%) than those outside capital cities (44%) (Australian
Bureau of Statistics, 2013).
A study was conducted by Imteaz, et al. (2011) to analyze the reliability of rainwater
tanks in Melbourne. The analysis was done using daily water balance model. The researchers
collected historical daily rainfall data from a rainfall station located near Melbourne city and
selected three representative years (wettest, average and driest) to use in the study (they wanted
to use the water balance model they had developed in three different climatic conditions – wet,
average and dry years). They performed reliability analysis of the rainwater tanks by considering
roof area, rainwater storage tank volume, per capita water consumption, total water demand
(determined by the family size) and the fraction of water demand supplied by the harvested
rainwater. The roof areas used in the analysis ranged between 50 m2 and 300 m2 while the size of
storage tanks ranged between 1,000 liters and 10,000 liters. The average number of persons per
household was between two and four whereas the average per capita water consumption was 185
liters/person/day. They presented several reliability charts, which showed that it was possible to
achieve 100% reliability if the RWHS comprised of a roof area of 150 m2 to 300 m2, family size
of two persons per household and storage tank size of 5,000 liters to 10,000 liters. They also

Rainwater Harvesting in Sydney, Australia 27
found that for a scenario where the family size is four persons per household, roof area of 300 m2
and storage tank size of 10,000 liters, achieving 100% reliability is not possible. This study
showed that it is possible to achieve 100% reliability for RWHS in Melbourne depending on the
scenario, which is determined by the number of persons per household (water demand), roof area
and storage tank size.
Taylor & Brodie (2016) conducted a study to investigate the potential of rainwater
harvesting in improving the hydrology of urban stream and supplementing municipal water
supply. They simulated the operation of dual-duty rainwater tanks located in different capital
cities of Australian states. The study found that the reliability and potential of rainwater tanks to
improve hydrology of urban stream and supplement municipal water supply varied across
Australian capital cities. This is mainly because of the varied climatic conditions (seasonality of
rainfall) in these cities. It was found that environmental benefits in some cases increased by 30%
while reliability of water supply when rainwater tanks were used fell slightly by 2%. On average,
rainwater tanks enabled 90% restoration of the desired stream flow. The study showed that
RWHS can significantly reduce the pressure on municipal water supply by providing water for
various uses and also help in protecting the environment by reducing runoff.
Chubaka, et al. (2018) investigated the implementation of regulations and incentives
created by the Australian Federal Government and other state governments to support adoption
of household RWHS in Australia. These regulations and incentives were created to promote use
of RWHS as a strategy to address the water sustainability concern. The researchers also explored
the potential health consequences associated with consumption of rainwater. It was found that
trace elements were present in rainwater but their levels were below the set standards apart from
in high industrial zones. Consumption of the rainwater did not increase the risk of

Rainwater Harvesting in Sydney, Australia 28
gastrointestinal disease hence this water can be used for both potable and non-potable purposes.
They also found that implementation of rainwater harvesting regulations and incentives is at an
advanced stage across Australia. This shows that RWHS has been universally accepted as a
reliable alternative source of water in the country. In a similar study, Amos, et al. (2018)
concluded that Australia has successfully and effectively managed her millennium drought and
this should be promising for developing countries that are facing water scarcity problem. They
also concluded that governments should provide rebates so as to lower the cost of rainwater
tanks and encourage more people to buy and install them in their homes.
Based on the above literatures, it is evident that RWHS is acceptable, common and being
used extensively in Australia. Most households in Australia have a rainwater tank and the
widespread implementation of RWHS has been largely supported by all levels of Australian
governments.
2.8. RWHS Research in Sydney
Rainwater harvesting has the potential of increasing water supply in Sydney and help reduce the
risks of water scarcity in the city. There are several studies that have been conducted on different
aspects of RWHS in Sydney.
Dbais, et al. (2010) investigated the sustainability of RWHS in multistory residential
buildings in Sydney. The motivation of this study was to focus on multistory residential
buildings because most of the previous studies were about detached small residential houses. In
this study, the sustainability of RWHS in multistory residential buildings in Sydney was
analyzed under different scenarios including variable catchment or roof area, number of building
floors, interest rate and water price, so as to determine the best combination that provided the
most suitable RWHS solution. The researchers created a hypothetical multistory residential

Rainwater Harvesting in Sydney, Australia 29
building and estimated water savings for different scenarios using a water balance model. They
also carried out a lifecycle costing. The main finding from the study was that financial benefits
and water savings were directly proportional to the roof area. This means that an increase in roof
area resulted to a corresponding increase in the financial benefits and water savings of the
RWHS for multistory residential buildings. The largest expenditures throughout the lifecycle of
the RWHS was the initial capital cost and maintenance cost. The financial viability of the RWHS
is also enhanced by increased water price system and lower interest rate. Therefore RWHS is a
sustainable solution for water shortage in both detached residential buildings and multistory
residential buildings under particular conditions and scenarios. Most importantly is that
initiatives such as government and/or economic incentives can help in reducing the capital and
maintenance costs of the RWHS, hence increasing the financial viability of the system.
Hajani & Rahman (2014) carried out a study to determine the cost and reliability of
RWHS in the outskirts of Greater Sydney. The main reason why rainwater tanks are used in
large cities is to save municipal water but in rural and peri-urban areas, these tanks are the only
source of water for most households. In this study, ten different locations in the suburbs of
Greater Sydney were investigated. Daily rainfall data for these locations was considered and
after analysis, it was found that a rainwater tank with a storage capacity of 5,000 liters could
meet 96-99% of laundry and toilet water demand for most households in the study areas.
However, the 5,000 liter rainwater tank could only meet 69-99% of laundry and toilet water
demand during the driest year. The lifecycle cost analysis revealed that the 5,000 liters tank
provided the highest benefit-cost range that ranged between 0.86 and 0.97, out of all the eight
tank sizes analyzed (1, 2, 3, 5, 7, 10, 15 and 20 liters tanks). In general, the reliability of RWHS
in the examined suburbs of Greater Sydney was very high during the wettest year and dropped

Rainwater Harvesting in Sydney, Australia 30
during the driest year. This means that it is vital to establish the right size of water storage tank
so as to collect more rainwater during the rainy season for use during the dry season.
According to a study conducted by Eroksuz & Rahman (2010), the water savings of
RWHS can be maximized by using larger storage tanks. In this study, the researchers explored
the potential of water savings of RWHS installed in multi-storey residential buildings in three
Australian cities: Sydney, Wollongong and Newcastle. It was found that the size of rainwater
storage tank determines the amount of water than can be saved by a RWHS. Larger tanks store
more water that can be used even in dry seasons. They also developed a prediction equation that
can be used to estimate the average amount of water that can be saved from a RWHS installed in
a multi-storey building in the three cities explored.
Imteaz, et al. (2013) analyzed performance optimization and cost-effectiveness of a
rainwater tank for Sydney metropolitan using eTank – a daily water balance model. The
performance and effectiveness of RWHS largely depends on the climatic conditions where it is
used. These conditions determines the most suitable size of rainwater storage tank. The
researchers in this study developed eTank using daily water balance analysis, which incorporated
daily rainfall, roof area, daily water demand, runoff, tank storage size and overflow. The
developed eTank was then used to analyze three different climatic conditions in Sydney area:
wet, average and dry years. It was found that rainfall data for at least five years should be used
when performing this kind of analysis to avoid erroneous results associated with using one year
rainfall data. Rainwater savings and reliability of RWHS were higher for central Sydney than
western Sydney because of rainfall variability in these two regions. To achieve 100% reliability,
a larger rainwater storage tank (>10,000 liters) should be used. It was also concluded that eTank

Rainwater Harvesting in Sydney, Australia 31
is an essential tool for use in analyzing the reliability and cumulative water savings, overflow
losses and needed water supply for any region.
In another study on the viability of RWHS in large buildings, Dbais, et al. (2012) used a
computer model called rainwater tank analysis model (RWTAM) to explore the potential of
water saving and financial viability of a RWHS in multi-storey residential houses in different
cities across Australia. For the case study in Sydney, a hypothetical multi-storey residential
building located in Botany Bay Council in Sydney was examined using RWTAM. Daily rainfall
data from 1946 to 2005 was obtained from the records at Sydney Airport station. The roof areas
of 800 m2 and 1,600 m2, site areas of 2,000 m2 and 4,000 m2, and a rainwater storage tank of size
75,000 liters were used for the study. For each of the two site areas, different floor layouts with
different number of floors and persons per floor were considered. It was found from the study
that water savings of a RWHS in Sydney increased significantly with increasing roof area and
water demand. The RWHS was likely to be financially viable if water prices in Sydney were
increased and interest rates lowered. Additionally, the largest component of the lifecycle cost of
RWHS was capital cost followed by maintenance cost. It was then concluded that the
government can promote adoption of RWHS in Sydney and other Australian cities by increasing
rebates for RWHS so as to minimize the financial burden of home owners who are interested in
buying and installing this system. This is another study that proves the feasibility and reliability
of RWHS in Sydney as long as the system is designed properly and the government provides
incentives to lower the capital cost.
Rahman, et al. (2012) conducted a study to investigate water savings potential, economic
benefits and reliability of RWHS in Greater Sydney. A total of 10 detached dwellings located in
different parts of Greater Sydney were selected for analysis. The researchers developed a daily

Rainwater Harvesting in Sydney, Australia 32
water balance simulation model and used it to examine water savings, financial viability and
reliability of different rainwater storage tank sizes (2 liters, 3 liters and 5 liters). It was found
from the study that the average annual rainfall is directly proportional to the average annual
water savings. This means that areas that receive more rainfall has the potential of saving more
water than dry areas. The 5 liter rainwater storage tank was also found to be preferable than the 2
liters and 3 liter storage tanks. The benefit cost ratios for all the three storage tanks examined
were less than 1 if government rebate was not provided, meaning that government incentives can
help increase the economic viability of RWHS. This finding suggest that relevant government
agencies in Sydney have to continue with or increase incentives so as to promote adoption of
RWHS by homeowners. Another finding was that homeowners can achieve the best financial
outcome by connecting their RWHS to outdoor irrigation, laundry and toilet. Maintain
A study conducted by Imteaz, et al. (2017) revealed that eTank is an accurate and reliable
tool for analyzing the performance and reliability of RWHS. In this study, the researchers used
eTank to explore a RWHS under three climatic conditions: wet, average and dry years. The
results obtained were then compared with the ones from other water balance models: Raintank
Analyzer and CSWBM. It was found that there was a significant difference between reliabilities
and water savings results obtained from eTank and CSWBM. However, the results obtained from
eTank and Raintank Analyzer were very close. The eTank was also used to predict water savings
in different climatic variations in Sydney and anticipated spatial variations in the city. Therefore
eTank has been proven to be accurate and efficient in analyzing the performance and reliability
of RWHS in Sydney.
Most of the above literatures have concluded that RWHS is a reliable and financially
viable alternative source of water in Sydney. This makes it necessary to conduct more research

Rainwater Harvesting in Sydney, Australia 33
on this topic so as to provide scientific roof on the applicability, feasibility and reliability of
RWHS in Sydney. It is through such studies that more people will learn about the benefits and
opportunities of using RWHS. In this study eTank will be used to explore the feasibility and
reliability of RWHS in Sydney. Therefore this study will improve the available knowledge on
the application of RWHS in Sydney, which is expected to encourage more people to harvest
rainwater and reduce reliance on municipal water supply.
2.9. Description of Study Area
The study area of this research is Sydney, which is the capital of New South Wales (NSW) state,
lying at 33°51'54.148" S and 151°12'35.6400" E coordinates and located on the Tasmanian Sea.
The elevation of Sydney is 19 meters and the city has a population of about five million people.
The Greater Sydney region covers an area of 12,367 km2 while the urban area of the city covers
an area of 1,687 km2. Figure 2 below shows the location of Sydney.
Figure 2: Location of Sydney

Rainwater Harvesting in Sydney, Australia 34
2.10. Climate of Sydney
Based on Koppen-Geiger classification system, the climate of Sydney is humid subtropical
climate (Cfa). This climate can also be described as temperature and humid. The climate is
generally experienced by regions located on each of the continent’s southeast side, usually lying
between latitude 25°and 40°, and most of these regions are located near or at coastal locations.
The climate of Sydney is characterized by cool to mild winters, warm and humid summers, and
uniformly distributed rainfall and sunshine all through the year. However, the first six months of
the year receives more rainfall than the last six months. The average temperature and rainfall
distribution of Sydney are as shown in Figure 3 below. The total annual rainfall is about 1,309
mm and even the driest month of the year (September) receives reasonable precipitation (60
mm). The weather of Sydney is moderated by the city’s closeness to the ocean. The rainfall
variability of Sydney is low to moderate and it is distributed through the months. Storms and
flooding are among the common weather patterns of Sydney. Heavy rain events in Sydney are
mainly caused by the east coast lows, black nor’easters, and wind directions. The city is prone to
drought but also receives sufficient amount of rainfall throughout the year. Thus the climate of
Sydney favors adoption of RWHS.

Rainwater Harvesting in Sydney, Australia 35
Figure 3: Temperature and rainfall distribution of Sydney (Climate-Data.Org, 2019)
2.11. Daily water balance model – e-Tank
There are numerous water balance modes used for analyzing the viability, reliability and
sustainability of RWHS. One of the most recent, accurate and now widely used water balance
models is eTank. This is an efficient and reliable daily water balance model that was designed to
consider a variety of factors including daily rainfall, water uses, area of the roof or catchment
area, water losses resulting from leakage, evaporation and spillage, and volume of rainwater
storage tank. (Imteaz, et al., 2011). This model only considers water usages inside the house and
does not consider water usages outside the house such as irrigation. There are other rainwater
harvesting analysis tools that consider water usages outside the house. One of such tool is
Raintank Analyser and continuous simulation water balance model (CSWBM). Each
geographical location has unique climatic conditions, which result to varied rainfall, water
demand and availability (Mehrabadi, et al., 2013). It is important to consider all these factors
when analyzing RWHS because they have significant impacts on the system. For instance, a

Rainwater Harvesting in Sydney, Australia 36
RWHS that is installed on a building in an area that receives less rainfall will collect a small
amount of rainwater hence the household will have to depend more on the municipal water
supply. On the other hand, a RWHS in an area that receives heavy rainfall will collect more
rainwater hence the dependence of the household on municipal water supply will be low.
The literature covered in this section show that numerous studies have been conducted to
establish the feasibility and reliability of RWHS in Sydney. Nevertheless, there is still need to
carry out more research so as to provide more scientific proof that RWHS can help solve the
problem of water scarcity in Sydney. Such studies should involve statistical, numerical and
analytical computations using advanced computer tools such as eTank. These tools developed
and used should also be able to predict potential water savings, economic benefits,
environmental benefits and reliability of RWHS in Sydney. Therefor this research will provide
very vital information that can be used by individuals, organizations or government authorities to
promote adoption of RWHS in Sydney and other parts of the world.
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Rainwater Harvesting in Sydney, Australia 37
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