Optimal use of Rainwater Tanks to
Minimize Residential Water Consumption
A thesis submitted in fulfilment of the requirements for the
degree of Masters of Engineering
Anirban Khastagir
B. Eng. (Hons)
School of Civil, Environmental and Chemical Engineering
RMIT University
July 2008
ii
DECLARATION
I certify that except where due acknowledgement has been made, the work is that of the
author alone; the work has not been submitted previously, in whole or in part, to qualify for
any academic award; the content of the thesis is the result of work which has been carried
out since the official commencement date of the approved research program; and, any
editorial work, paid or unpaid, carried out by a third party is acknowledged.
Anirban Khastagir
iii
ACKNOWLEDGEMENTS
It is with pleasure that I express gratitude to many people who provided me sincere support
during the period of study.
This thesis would not have been achievable without the technical guidance, indefatigable
support, the incisive critiques, the pragmatic queries, and the patience of my thesis
supervisor Dr. Nira Jayasuriya. I thank her from the bottom of my heart.
I remain indebted to my family members both at home in Bangladesh and overseas for
providing me the encouragement to carry out my research for the last two years.
Last but by no means least; I would like to thank my dear parents, Haripada Khastagir and
Late Dipika Khastagir. Nothing I can say to justify my feelings about their bona fide
adoration, support and encouragement they provided throughout my life. I am grateful to
Omnipotent God for the gift of such caring parents.
iv
TABLE OF CONTENTS
DECLARATION ..........................................................................................................ii
ACKNOWLEDGEMENTS ..........................................................................................iii
TABLE OF CONTENTS.............................................................................................iv
LIST OF TABLES ....................................................................................................vii
LIST OF FIGURES...................................................................................................xii
ABBREVIATION
............................................................................................................. xvi
ABSTARCT
................................................................................................................... xviii
CHAPTER 1. INTRODUCTION ............................................................................................. 1
1.1.
M
OTIVATION
.................................................................................................................. 1
1.2.
S
COPE
.......................................................................................................................... 3
1.3.
O
BJECTIVE
.................................................................................................................... 4
1.4.
P
OSSIBLE OUTCOMES OF THIS RESEARCH
....................................................................... 4
1.5.
L
AYOUT OF THE
T
HESIS
.................................................................................................. 5
CHAPTER 2. LITERATURE REVIEW ................................................................................... 6
2.1.
I
NTRODUCTION
.............................................................................................................. 6
2.2.
S
IGNIFICANCE OF
A
LTERNARIVE WATER SOURCE
............................................................................
6
2.3.
A
R
EVIEW OF CURRENT PRACTICE
.................................................................................. 8
2.3.1. Current guidelines for selection of tank size ........................................................ 10
2.4.
P
OPULATITY OF RAINWATER TANKS
............................................................................... 14
2.5.
R
EVIEW OF USE OF ALTERNATIVE WATER SOURCE
......................................................... 19
2.6.
S
UMMARY AND
C
ONCLUSIONS
...................................................................................... 22
CHAPTER 3. VARIATION IN TANK SIZES WITH THE GEOGRAPHIC LOCATION AND
THE DEMAND..................................................................................................................... 25
3.1.
I
NTRODUCTION
............................................................................................................ 25
3.2.
O
VERVIEW OF STUDY AREAS
........................................................................................ 26
3.3.
R
AINFALL
D
ATA
........................................................................................................... 28
3.3.1. Filling in missing data ....................................................................................... 29
3.4.
D
ATA
A
NALYSIS
........................................................................................................... 30
v
3.4.1.Statistical techniques fo data analysis between observed and simulated data ..... 33
3.5.
E
STIMATION OF RAINWATER TANK SIZE
.......................................................................... 33
3.5.1. Development of rainwater tank model .............................................................. 33
3.5.2. Determination of roof runoff (Q)........................................................................ 35
3.5.3. Determination of demand for water (D
t
)............................................................ 36
3.6.
C
OMPARISON WITH
WSUD
M
ODEL
............................................................................... 40
3.7.R
ELATIONSHIP BETWEEN TANK SIZE AND RELIABILITY FOR DIFFERENT STATIONS IN THE
STUDY AREA
……………………………………………………………………………………….40
3.8.
S
PILLAGE AND UDAGE OF RAINWATER FROM A TANK
....................................................... 48
3.9.
S
UMMARY AND CONCLUSIONS
....................................................................................... 54
CHAPTER 4. DEVELOPMENT OF A METHODOLOGY TO CALCULATE OPTIMUM TANK
SIZE .................................................................................................................................... 56
4.1.
D
ERIVATION OF DIMENSIONLESS NUMBERS
.................................................................... 56
4.2.
D
ERIVATION OF DIMENSIONLESS NUMBERS
.................................................................... 56
4.2.1. Dimensionless Analysis.................................................................................... 56
4.2.2. Relationship between dimensionless numbers ................................................. 59
4.3.D
EVELOPMENT OF A GENERALIZED CURVE TO OBTAIN THE OPTIMUM TANK SIZE
................. 65
4.4.
V
ERIFICATION OF THE DEVELOPED CURVE
..................................................................... 67
4.5.
A
NALYSIS OF THE GENERALIZED CURVE
........................................................................ 88
4.6.
S
UMMARY
A
ND
C
ONCLUSIONS
...................................................................................... 93
CHAPTER 5. SIMULATING THE CONTRIBUTION OF RAINWATER TANKS TO
MANAGING MELBOURNE'S DOMESTIC WATER DEMAND ............................................ 95
5.1.
I
NTRODUCTION
............................................................................................................ 95
5.2.
S
TUDY
A
REAS
............................................................................................................. 97
5.3.
S
IMULATION OF RAINFALL DATA
.................................................................................... 98
5.3.1. Thiessen polygon method................................................................................. 99
5.4.
D
ETERMINATION OF POTABLE WATER SAVING EFFECIENCY
........................................... 102
5.5.
WATER SAVING EFFECIENCY AND SCENARIO TESTING
................................................... 104
5.6.
C
OMAPARISON OF WATER SAVING EFFECIENCY
........................................................... 112
5.7.P
OTABLE WATER SAVING EFFECINCY
(
UNDER NO WATER RESTRICTION
).......................... 114
5.8.
S
UMMARY AND CONCLUSIONS
..................................................................................... 117
CHAPTER 6. IMPACTS OF RAINWATER TANKSON MANAGING STORMWATER RUNOFF
HARVESTING AND QUALITY…………………………………………………………………...120
6.1.
I
NTRODUCTION
.......................................................................................................... 120
