VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

TRAN DIEU LINH

CONSIDERATION OF EXISTING
RAINWATER HARVESTING SYSTEM AND
ITS ENHANCEMENT USING MEMBRANE
FILTRATION AND UV-IRRADIATION
MASTER'S THESIS
Environmental Engineering

Hanoi, 2019


VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

TRAN DIEU LINH

CONSIDERATION OF EXISTING
RAINWATER HARVESTING SYSTEM AND
ITS ENHANCEMENT USING MEMBRANE
FILTRATION AND UV-IRRADIATION
MAJOR: Environmental Engineering
CODE: Experimental
RESEARCH SUPERVISOR:
Principal Supervisor: Professor. Jun Nakajima
Co-Supervisor: Professor. Naoyuki Kamiko

Hanoi, 2019


ACKNOWLEDGEMENT
First and foremost, I would like to express my heartfelt gratitude to my two brilliant
supervisors, my main supervisor, Professor Jun Nakajima and my co-supervisor,
Professor Naoyuki Kamiko. To Professor Jun Nakajima: Thank you for accepting me
as your student and helping me to find out my interest in studies of rainwater treatment.
Thank you for your outstanding guidance, continuous inspiration and support in my
two-year research. I appreciate the in depth discussions which have sharpened my
thought process and shown me how to transform my mistakes into skills. To Professor
Naoyuki Kamiko: Thank you for all the instructive advices and valuable knowledges
you have provided me during my research work as well as my internship in
Ritsumeikan University, Japan. I am truly grateful to have such a fulfilling experience
working with you, which contributes no small part to my achievements.
I am indebted to my mentor, Professor Jun Nakajima: Thank you for being a good
mentor and for guiding me on the right path as well as providing me with the necessary
materials and knowledges to work with my project. Moreover, your creative ideas
about the projects have impressed and inspired me a lot. To be honest, you are not only
my respectable supervisor but also my beloved grandfather.
In addition, I highly appreciate Professor Hiroyuki Katajama, Associate Professor
Kasuga Ikuro, Doctor Nguyen Thi An Hang, Mrs. Nguyen Phuong Thao and Mrs. Dinh
Dieu Anh for their patience in guiding and assisting me through my Master course.
I would also like to extend my appreciativeness to my fellow lab mates who have been
working with me and sharing their experience and knowledge to me. Thank you for all
the joy, laughter and friendships to help me get over the stress of after-hours work and
make my research much easier. In addition, I would like to send my special thanks to



my classmate, Mr. To Hoang Nguyen for his supports in my experiments and writing
as well.
Eventually, I would like to thank my beloved family and friends for their deep love and
support that enables me to concentrate on my pursuits. Without their encouragement,
this work cannot be done.


CONTENT
Chapter 1.

Introduction and objective .................................................................... 1

1.1. Background ......................................................................................................... 1
1.2. Problem statement .............................................................................................. 2
1.3. Objectives ........................................................................................................... 5
1.4. Structure of the thesis ......................................................................................... 6
Chapter 2.

Literature review .................................................................................... 7

2.1. Introduction of rooftop rainwater harvesting..................................................... 7
2.1.1.

Definition and history ............................................................................... 7

2.1.2.

Advantages and disadvantages of using rainwater harvesting ............... 11

2.1.3.


Components of rooftop rainwater harvesting system ............................. 12

2.2. Quality of harvested rainwater ......................................................................... 16
2.2.1.

Factors affecting rooftop harvested rainwater quality............................ 16

2.2.2.

Physico-chemical quality of rooftop harvested rainwater ...................... 16

2.2.3.

Trace organics ........................................................................................ 19

2.2.4.

Microbial quality of rainwater harvesting systems ................................ 20

2.2.5.

Case study in Vietnam ............................................................................ 24

2.3. Rainwater treatment and disinfection methods ................................................ 26
2.3.1.

Membrane filtration ................................................................................ 27

2.3.2.


Chemical disinfection ............................................................................. 28

2.3.3.

UV irradiation ......................................................................................... 29

Chapter 3.

Methodology .......................................................................................... 31


3.1. Web survey of rainwater harvesting manuals in the world .............................. 31
3.2. Questionnaire survey of rainwater harvesting situations and people’s attitude .
.......................................................................................................................... 31
3.3. Examination of rainwater purification in a typical existing RWH ................... 32
3.3.1.

Sampling area ......................................................................................... 32

3.3.2.

Commercial filter containing RO in combination with UV lamp .......... 34

3.3.3.

UV submersible germicidal System ....................................................... 36

3.3.4.


Measurement of physicochemical quality .............................................. 37

3.3.5.

Measurement of microbiological quality ............................................... 38

Chapter 4.

Results and discussion .......................................................................... 40

4.1. Web survey of rainwater harvesting manuals in the world .............................. 40
4.1.1.

Purpose of using rainwater ..................................................................... 40

4.1.2.

Structure and materials for rainwater catchment roof ............................ 41

4.1.3.

Design and material for gutter ................................................................ 43

4.1.4.

Installation type and material for storage tank ....................................... 44

4.1.5.

Disinfection methods .............................................................................. 46


4.1.6.

Number of explanation contents............................................................. 47

4.2. Questionnaire survey of rainwater harvesting situations and people’s attitude .
.......................................................................................................................... 48
4.2.1.

Overlook of current situation in the area of study .................................. 49

4.2.2.

Willingness to use our introduced rainwater treatment systems ............ 52

4.3. Examination of rainwater purification in a typical existing RWH ................... 54
4.3.1.

Rainwater quality ................................................................................... 54


4.3.2.

Combination system of RO purifier and UV sterilizer .......................... 56

Physicochemical properties .................................................................................... 56
Microbiological properties ..................................................................................... 58
4.3.3.
Chapter 5.


Submerged UV lamp .............................................................................. 59
Conclusion ............................................................................................. 61

References ..................................................................................................................... 62
Appendix I..................................................................................................................... 71
Appendix II ................................................................................................................... 76
LIST OF FIGURE
Page
Figure 2.1. A cistern in Yerabatan Sarayi, Istanbul in Turkey ........................................ 9
Figure 2.2. A common RWH system ............................................................................. 13
Figure 2.3. Floating ball first flush diverter ................................................................... 15
Figure 2.4. Working mechanism of reverse osmosis filter ............................................ 28
Figure 3.1. Sampling location of questionnair survey (Google Maps, 2019) ................ 32
Figure 3.2. Pictures of the pilot of rainwater harvesting system (a: Catchment roof, b:
Storage tank) .................................................................................................................. 33
Figure 3.3. Design of DEWX RO AQUAPRO Serise AP-60 supplied by DEWX
Vietnam .......................................................................................................................... 34
Figure 3.4. Sampling scheme of the examination of RO purifier in combination with
UV lamp ......................................................................................................................... 36
Figure 3.5. Examination system of submerged UV sterilizer ........................................ 37
Figure 4.1. Purpose of using rainwater (a: Total;b: Developing countries, c: Developed
countries). ....................................................................................................................... 41
Figure 4.2. Different structure of roof ........................................................................... 41


Figure 4.3. Materias for roof (a: Total; b: Developing countries; c: Developed
countries) ........................................................................................................................ 42
Figure 4.4. Shapes of gutter ........................................................................................... 43
Figure 4.5. Material for gutter (a: Total; b: Developing countries; c: Developed
countries) ........................................................................................................................ 44

Figure 4.6. Type of tank ( a: Developing countries; b: Developed countries)............... 45
Figure 4.7. Materials for tank (a: Developing countries; b: Developed countries) ....... 45
Figure 4.8. Disinfection methods(a: Developing countries; b: Developed countries) ... 46
Figure 4.9. Histogram of number of contents in a manual ............................................ 47
Figure 4.10. Number of family member ........................................................................ 49
Figure 4.11. Types of water used ................................................................................... 49
Figure 4.12. Percentage of families use each type of water ........................................... 50
Figure 4.13. Monthly water bill ..................................................................................... 51
Figure 4.14. Purpose of using rainwater ........................................................................ 52
Figure 4.15. Types of water treatment ........................................................................... 52
Figure 4.16. Willingness of residential people to use the introduced water treatement
system( a: RO (4.000.000 VND); b: UV lamp (700.000VND); c: combine system
(RO+UV)) ...................................................................................................................... 53
Figure 4.17. Microoganism concentration in Raw water (a: Total Coliforms; b: E.coli)
........................................................................................................................................ 56
Figure 4.18. pH change through the system................................................................... 57
Figure 4.19. Conductivity change through the system………………………………...57
Figure 4.20. Dissolved oxygen change through the system; Figure 4.21. Turbidity
change through the system ............................................................................................. 57


Figure 4.22. Change in microoganism concentration through the system (a: Total
Coliforms; b: E.coli ........................................................................................................ 58
Figure 4.23. Change in microoganism concentration vesus time interval (a: Total
Coliforms; b: E.coli)....................................................................................................... 59


LIST OF TABLES
Page
Table 1.1 Heavy metal concentration in tap water districts in Hanoi ................................. 5

Table 2.1. Concentration of E.coli in storage tanks of roof-harvested rainwater (adapted
from K. Hamilton et al, 2018) ........................................................................................... 21
Table 2.2. Chemical and microbiological characteristic of harvested rainwater before
and after treatment ............................................................................................................. 24
Table 3.1. Components of DEWX RO AQUAPRO Serise AP-60 supplied by DEWX
Vietnam ............................................................................................................................. 34
Table 4.1. Quality of rainwater in storage tank................................................................. 54


LIST OF ABRREVIATION

CFU

Colony forming unit

DO

Dissolved Oxygen

E.coli

Escherichia coli

ND

None Detected

NG

Not Given


RO

Reverse Osmosis

RWH

Rainwater harvesting

UV

Ultraviolet

μS

Micro Siemen

NTU

Nephelometric Turbidity Units


CHAPTER 1.
1.1.

INTRODUCTION AND OBJECTIVE

Background

For thousands years, through big cities to deserts, human has fought to sustain oneself

by the management of vital, especially water. It is clear that water is one of the cardinal
resources in the world which takes an important role to ensure the live of all spices and
propose a part of larger ecosystem (Connor, 2015). In addition, one of the important
index indicating the development of a country is the sustainability of water (Villholth
et al., 2010). According to the definition of European Union (EU) Water Framework
Directive (WFD), “Water is not commercial product like any other but, rather, a
heritage which must be protected, defended and treated as such”. It is possible to
predict the availability of water in the natural water cycle without the interference of
human. However, because of human activities and intrusions including wetland
drainage, deforestation as well as other means of pollution, the ecosystem and natural
sequence have become unbalance. As a result, the world is now facing various water
related issues and it has been reported that one third of population in the word is now
facing the consequence caused by water scarcity (De Silva et al., 2007). Beside the
issues of water availability, the issues of available water quality are even more critical.
Water scarcity and pollution issues lead to health issues due to the water borne disease
exposure. In the case water stress occurs, people would consume any source of water
they can reach without confusing of water quality, in this case, lack of water leads to
lack of water quality. In a study in 2007, Alcamo and colleges analyzed a scenario
exploring the change to 2050 in average annual water availability. According to the
observed results, precipitation in many parts of the world was predicted to increase
leading to the growth in water availability in these areas. On the other hand, increasing
1


air temperature also results in the increase of evapotranspiration, consequently water
availability reduces. The evapotranspiration and precipitation interact differently on
water availability in both positive and negative way, however the evapotranspiration
was proofed to overshadow the increase in precipitation because the temperature
increases almost everywhere in the world (Alcamo et al., 2007). It is clear that climate
change put a lot of visible effects on the limitation of water. In addition, the

improvement of socioeconomic condition increase the population day by day,
meanwhile the more the world develops the more water is required. In this condition,
what will happen to water supply and demand? How to make the situation of water
resource better?
For that reason, toward the sustainable development of our earth, the sustainability of
water sources is needed. Since 4500 B.C, rainwater harvesting (RWH) system had been
popularly applied in the southern Mesopotamia (Iraq) inhabitants and inhabitants from
other Middle Est countries. After thousands years, the use of this type of water has
become more and more interested in both developed countries and developing
countries, from rural area to urban area. By applying RWH systems, human can control
storm water runoff to natural reservoirs and depressions as well. Furthermore, other
usages of rainwater are supplying household water including drinking water and
irrigation water as well as injecting into the ground in order to replenish supply of
groundwater. Moreover, by using in-situ harvested rainwater, carbon footprint caused
by water collection and distribution can be reduced and the cost of transporting water
reduces as well (Harb, 2015).
1.2.

Problem statement

World Health Organization (WHO) reported that 783 million in the world, about one
per 10 people cannot access to improved water. Furthermore, around 2.5 billion people
– more than one third of planet population still lack proper sanitation. This problem is

2


specially serious in Asia, where is home of around 4.5 billion people. Compare to other
areas in the world, Asia countries are now in the worse condition than other parts in the
availability of water according to UNESCO report. The water availability in Asia area

only counts for 36% of the total water in the world meanwhile 60% of the world
population is in this area (World Water Assessment Programme, 2003). Positively,
among the number of people accessing to safe water, 47% are from China and India
due to the economic growth and consideration on standard of living in both nations.
Located in Asia’s Southeastern part, Vietnam is home of over 86 million people with
$3100 of estimated GDP per capita. Almost two-thirds of Vietnam population lives
along three main river basins of the country, which are Dong Nai, Mekong Delta and
Thai Binh. The country has 10km of rivers in total consisting 2360 rivers, therefore the
amount of water supply seems to be enough for the nation (The Water Project, 2019).
However, because of the limited financial capacity and the lack of infrastructure along
with an uneven rain distribution, many parts of Vietnam still have to deal with water
shortage situation. Despite of the improvement in water supply infrastructure and
management recently, the situation in many rural parts of Vietnam which are often the
poorest area of the countries has not been improved so much. I has been reported there
is only 39% people living in the rural area can access to improved water and sanitation.
In some recent decades, the rural residents have changed from surface water obtained
in shallow dug well to the pumped groundwater from private tube wells (The Water
Project, 2019). In the peri-urban area of Hanoi and several communities locating in the
Northern part of Vietnam, arsenic contamination has been reported in the drinking
water which is supplied from groundwater source (Agusa et al., 2006; Nguyen et al.,
2009). Millions people living in these area have a severe risk of arsenic poisoning.
High concentration of arsenic can cause cancer, skin and neurological problem for
human. Furthermore, the recent rapid economic development in the country causes
serious stress on river water quality due to the increase in various toxic compounds

3


discharged. The rivers surface water is locally contaminated by organic pollutants such
as oil and solid waste discharged from industries and livestock activities. In addition,

the special geography and topography of the country also lead to several hazards
including storms, floods, typhoons and drought. These hazards result in many water
issues such as waterborne diseases and water pollution which may put impacts on
livestock and agricultural lands and the nation’s public health. According to a report of
the Ministry of Natural Resources and Environment, 80% of the diseases caused for
Vietnamese are waterborne diseases. The popular waterborne diseases found are
dysentery, malaria, typhoid and cholera. There is no doubt that in Vietnam, agriculture
consumes the highest amount of water because this country is one of the largest
provider of rice in the world. More than 80% of water production is used for
agriculture. Water resources are significant resources because they are not only natural
sources but also sources of economic, social as well as cultural activities. In recent
decades, the government of Vietnam has attempted to develop water resources
management issues by implementing related policies and programs. However, there are
still some challenges including improving access to safe water and clean sanitation in
both urban and rural area, improving public participation, knowledge as well as
strengthening management of river basin. According to the data collected in 2015, 98%
of Vietnam total population can access to clean water, which means that nearly 2
million people in the country still cannot access to clean water, especially in the rural
areas (WHO/UNICEF, 2015).
Regarding the quality of current water supply in Hanoi, Vietnam, Table 1.1 presents
the situation of water supply in some district in Hanoi in parameters of heavy metal.

4


Table 1.1. Heavy metal concentration in tap water districts in Hanoi
Concentration of heavy metal (ppb)
District
As


Cd

Cr

Cu

Fe

Mn

Mo

Ni

Pb

Se

Zn

Hoan Kiem

12.2

0.2

13.5

2.5


66.4

12.8

ND

10.4

6.1

0.1

2623

Dong Da 1

2.4

0.3

21.8

23.6

123

5.5

ND


16.5

7.1

0.4

60

Dong Da 2

11.8

0.3

15.3

14.6

96.9

4.2

ND

12.6

6.9

0.4


94.1

Ha Dong

9.1

0.3

17.3

10.1

136

62.2

0.2

12.3

7.8

ND

554

Hoang Mai

20.7


0.8

15.0

17.3

217

234

0.2

11.5

31.2

0.2

444

Tu Liem

0.8

0.2

14.6

4.9


67.6

7.4

ND

11.7

6.2

ND

23.5

Gia Lam

1.1

0.2

15.6

7.5

111

5.1

ND


11.7

6.9

ND

69.9

For a short conclusion, the country is gradually getting into a water scarcity scenario
and tenable ways are needed to strengthen the availability of water.
1.3.

Objectives

1.

To clear the situation of RWH around the world and compare between

developing and developed countries.
2.

To clear the current situation of RWH and people's attitude in a peri-urban area

in Hanoi, Vietnam.
3.

To clear the applicability of existing water treatment devises to RWH for

reduction of pathogenic risk.


5


1.4.

Structure of the thesis

This Thesis comprises of 5 chapters. In the first chapter, the certain key aspect of this
study is generally introduced. The chapter starts with a brief background of global
water cycle and distribution followed by the problem statement and the objectives as
well as the expected contribution of the study. The structure of this thesis is given at
the end of chapter 1.
Chapter 2 presents an overview of RWH systems with their history and also the
components of harvesting systems followed by the quality of rainwater harvested and
treatment methods for purposes of use.
Chapter 3 explores the methodological framework of the study including sampling
strategy and questionnaire surveys with residents in the area of research.
Chapter 4 focuses on analyses of obtained results in this research and the discussion of
the analyzed results.
Chapter 5 is the last chapter of the study and it gives the conclusions observed from the
results in chapter 4. Recommendations and prospects for the future are also part of this
chapter.

6


CHAPTER 2.
2.1.

LITERATURE REVIEW


Introduction of rooftop rainwater harvesting

2.1.1. Definition and history
Definition
The concept of “Rainwater harvesting” simply involves all those techniques of
collection and storage rainwater in natural reservoir or tank for subsequent utilization
rather than of allowing it to run off. The term has been used to accumulation and
storage of rainwater in mini-scale resources of water; in addition this term refers to the
activities with purposes of harvesting surface and other hydrological studies and
engineering interventions regarding the limited water enforcement (Patel et al., 2014).
Rainwater is normally collected from the roofs of buildings or from other impermeable
surfaces. Therefore, rooftop water harvesting (RRWH) is considered as an important
sub set of RWH. This study covers only rooftop RWH.
History
It has been written in history that rainwater collection and storage techniques have
started to be applied since thousands of years when human first started to farm the land
and new methods of irrigating crops were required. However, there are many changes
have taken on materials and design of harvesting systems through thousands years to
improve the performance of harvesting rainwater.
Archeological evidence showed that the concept of RWH and evidence of this green
technology may trace back more than 4000 years. The use of cisterns for rainwater
storage can date back to the Neolithic Age. In Southwest Asia, by late 4000 B.C,
waterproof lime plaster cisterns were built largely to keep rainwater for farming. In

7


India, Mesopotamia, China, and Israel, rainwater was captured as early as 2.000 B.C.
Harvesting technologies in the Indus Valley were extremely advanced. In many ancient

cities in Indus Valley which still remain today, it is easily to find huge vats cut into the
rock for accumulation of rainwater. During dry time of the year, these vats were used
to keep the citizens and local agriculture going (Gupta and Agrawal, 2015). By that
time, the basic design of RWH systems includes a large rock formed into a basin using
clay and other rocks to seal it from leaking. The storage cisterns for hillsides runoff
water employed to agricultural and domestic use still remain today. Additional
evidence of RWH via an extremely large cistern in Jerusalem since 2500 B.C has been
found. Dating back to 1700 B.C, other evidence of large cistern were also found in the
Greek Isles (Rotoplas, 2018). In the southwest United State, Anasizi and other Native
American ancient residents used to allow rainwater flow into the villages or cliff
dwellings for livestock activity and drinking; the water flowed following the natural
contours of plateaus and mountains by the carefully crafted purveyance trenches.
Meanwhile, in the North America cultures, because of rainwater softness whereas
groundwater shows high hardness, it was early gathered rainwater in barrels for daily
activities such as bathing, laundering and other cleaning chores (Gould and NissenPetersen, 1999).
In most of ancient cities, including Roman, the urbanization and increase of population
led to the increase in demand of water for housing including both potable and nonpotable purpose. As a result, covered cisterns had developed. The cisterns were
constructed underneath the courts. The underground design shows two main
advantages: firstly, this kind of cistern increases the volume of rainwater stored and
decreases the evaporation losses of water inside tank. Secondly, by applying
underground cisterns, rainwater inside can be protected against pollution. In rain event,
all the rainwater from the rooftops ran into the pools then the overflow flowed into the
cisterns. By that time, the harvesting techniques were decentralized and this is

8


considered as the reason why RWH lost their momentum with the increase of use and
the development of a centralized supply from spring channel into the urban areas.
However, it is uncommon to see centralized RWH and storage in cistern. The largest

cistern in the world is found in Yerabatan Sarayi, Istanbul in Turkey. The cistern was
built by Byzantine Emperor Justinian I (527-565 A.D) and named as arasında
Yerebatan Palace and measures 140 by 70 metres. The capacity of storage is 80.000 m3.
The underground structure is based on intersecting vaults.

Figure 2.1. A cistern in Yerabatan Sarayi, Istanbul in Turkey
Another other cistern with high capacity of 50.000 m3 was also found named Binbirdik.
There is a document suggests that Binbirdik was built under Caesar Constantine (A.D.
329 – 337). Both above cisterns are centralized storage. In this systems, rainwater was
collected from paved streets and roofs and a sophisticated system of filters assured
clean water (Hasse, 1989). However, the systems like cisterns in Istanbul is no longer
used in and only considered as examples of centralized RWH systems. Two main
reasons for the lack of use of this system are proposed: firstly, the construction cost of
underground cisterns is higher than the construction of the above one; secondly human
excrete can cause pollution for the water storage in underground cistern.

9


Although RWH systems with closed cisterns were not favored in other reasons as in
ancient Rome, sometime they were still found in the semi-desert areas at home scales
where the owners did not want to build wells or springs in their house. The Christian
monks also built monasteries with this kind of system. Other examples of closed
cisterns system were found in monasteries in Mexico and in former Spanish Empire.
These above example of such a complicated system proof the high quality of design
and construction in ancient time.
However, the use of RWH system became less favorable following the increase of
urbanization. The assumed reason is that during the industrial age, larger amounts and
higher quality of water were required, safe water suppled via pipes are more popular.
But supplied water not only shows advantages but also have a lot of disadvantages as

following:
-

In the bad natural conditions for example earthquakes, or because of the

destruction caused by war as well as source pollution including environmental
pollution through chemicals); the supply of water will be totally cut-off.
-

The convenience access of supply water leads to the wastage of using water, it is

understandable. In addition, water which is one sources of life has become a
commodity of consumption and also played the contradiction between suitable
management of water and economy expansion.
However, in urban areas nowadays, it is hard to find an alternative to a centralized
water supply.
After thousands years, RWH is once again gaining importance in human life in rural
areas particularly in developing countries due to the increase in water demand which
requires all possible sources of water (Climateincorp.com, 1996)

10


2.1.2. Advantages and disadvantages of using rainwater harvesting
Advantages of using rainwater
The use of rainwater shows many benefits over supplied water and ground water. First
of all, it is easy to maintain the water and harvesting system. Simple technology can be
employed to construct this type of system. The overall cost for installing and operating
is much lower than that of water pumping system. As a result, RWH is a sustainable
choice for source of water. In addition, rainwater can be storage in cisterns for use

during time meanwhile supplied water can be cut-off in some special conditions.
Secondly, for many households and small businesses, using rainwater even for nondrinking purpose of drinking purpose can reduce their water bill. For industrial scale
and large business, harvested rainwater can also be used for many operations instead of
depleting the nearby water sources. Thirdly, the population increases leads to the
continuous increase in water demand. As a result, high amount of groundwater is
extracted to fulfill the daily life. Therefore, groundwater which has gone to significant
low level in some areas where there is huge water scarcity depletes. By using rainwater,
the need of groundwater can be decreased. In addition, it has been reported that RWH
system results to reduce soil erosion and floods. In low lying areas, collecting water in
storage cisterns can reduce floods. Moreover, soil erosion and surface water
contamination by pesticides and fertilizers from run-off of rainwater can also reduce,
hence lakes in ponds can be cleaner. Finally, although there are some studies
recommend that rainwater before treatment cannot be used for drinking, rainwater can
be used for many different non-potable purposes. From chemical contamination aspect,
rainwater is free from many chemicals which are found in groundwater, therefore,
rainwater is suitable for watering gardens and irrigation. In the areas where have to
commonly face to forest fires and bush fires in summer, storing rainwater in large

11


reservoir can be considered as a wonderful idea. In addition, collected rainwater can
also be used for toilets flushing, washing house and clothes etc.
Disadvantages of using rainwater
Although there are many advantages of using rainwater, some disadvantages also exist.
Unpredictable rainfall is a biggest drawback of harvesting rainwater. It is hard to
predict rainfall and the supply of rainwater can be limited because of little or no rainfall.
Rainwater use is suitable in the areas with high level of rainfall. Second disadvantage is
requirement of regular maintenance because rainwater in cisterns is easy to get prone to
mosquitoes, rodents, insects, algae growth and lizards. The tanks can become as good

environment for many insects and animals if they are not maintained properly. Third, if
the materials chosen for roof, gutter, pipe and tank are not safe and suitable to the area
condition, microbiological and physicochemical pollution can occur easily. Forth,
rainwater requires large storage tank to reach the demand of use during year, it takes a
large area in the house.
RWH system is gaining speed over time, especially in the areas with plenty of rainfall
(Conserve Energy Future, n.d)

2.1.3. Components of rooftop rainwater harvesting system
Historically, principle of rooftop RWH system is quite simple: rainwater run from
roofs to tanks. A common RWH system contains four main components: (1) catchment
surface (roof), (2) conveyors followed by (3) filter and (4) storage tanks (J. Song et al.,
2009).

.

12


Figure 2.2. A common RWH system
Below is a brief overview of each component.
(1) Catchment surface
The performance of rainwater catchment highly depends on texture of the catchment.
The smooth and impervious surfaces lead to better water quality. Waterproof materials
which absorb less water and do not give chance for microbes and dirty particles to
accumulate in the pores and seams may give better quality of water harvested. In
addition, the smoother the surfaces are, the faster rainwater flows through and the
cleaner the surfaces are. For the best quality of water generated, suitable materials are
clay, metal and concrete. There are several types of roofing material which are not
suitable for rainwater due to components leaching. For example, roofs made by copper

or affected from fungicides, pesticides and herbicides are warned not to be employed.
Furthermore, untreated metal such as galvanized roofs are not appropriate to the roof
material because zinc leaching can cause harmfulness to vegetation. Because rainwater
can dissolve minerals in catchment surface components then carry them flowing to the
storage system. Rainwater harvested forward potable purpose should not runoff from
13


roofs which contain untreated metal including copper, zinc coatings, asbestos or
contaminated by lead flashing, lead-based and other harmful chemicals as well as
biocide compound.
(2) Conveyance
Another important component of the system is conveyance which channels rainwater
from catchment area to storage area by gutters connected to downspouts. Half round
gutter are prefer to the square and V-shape one because it display high performance in
avoiding joint seams in the system to reduce debris catching and bacterial and algae
growing. Regarding structure, an outer edge higher than roof-side edge and has splash
guards of roof valleys and slope towards downspout is highly recommended. To reduce
the debris accumulating in the angle then blocking the flow, angle in downspout pipe
should be less than 45 degrees. The most common material for gutter and downspout
are metal and PVC, in some lower income area, bamboo and wood are also options.
(3) Pre-filter and first flush
Rainwater runs from catchment surface can pick up debris and leaves on the way.
Therefore, pre-treatment items should be included in the system before water runs into
cisterns. Debris excluder of similar filter can prevent the accumulation of needles,
leaves and other debris. Moreover, to larger debris, rainwater can dissolve or pick up
materials too fine for the screens to filter out. In order to catch these pollutants, when
any rain event occurs, the very first part of rainwater running from the catchment area
should be diverted from the storage tank, the diverter is called “first-flush” diverter.
The “first-flush” water contains the highest concentration of debris, pollen and animal

feces as well as pesticides and other airborne residues.
There are several types of diverters which can be employed, all of them need to be
installed before the storage tank. The design of diverter can be very simple which has a
PVC standpipe in connection to a downspout. The simplest first-flush diverter consists
of a PVC standpipe connected to a downspout. In this design, the standpipe play role as
14