One of the most pressing concerns confronting developing countries is the provision of safe drinking water for both urban and rural residents, particularly those living in areas remote from natural surface water sources such as rivers and lakes. Other internal factors, such as rising population pressure and conflict, privatization, illegal settlement, changing tenure arrangements, poverty, socio-economic differentiation, and environmental degradation, also have an impact on the quality, accessibility, and dependability of water supplies. In Malaysia, some rural areas are not connected to the potable water supply grid. The water source is mainly from the nearby river, which is of poor quality, especially in the areas exposed to logging activities. Malaysia’s river water is usually polluted or contaminated, resulting in many waterborne diseases
[1]
. Other developing countries also usually face this problem
[2]
[3]
.
The Sarawak government has made numerous efforts to provide a clean drinking water supply. The main water suppliers in Sarawak are the Kuching Water Board (KWB), Sibu Water Board (SWB), Northern Region Water Board (NRWB), and the Sarawak Rural Water Supply Department (JBALB)
[4]
-
[6]
. The function of JBALB is to supply hygienic water to the rural residents, and their goal is to ensure 100% coverage for all rural residents by the year 2025 under the Sarawak Alternative Water Supply (SAWAS) programme
[7]
. SAWAS focuses on building centralized water treatment plants for larger rural communities through the ultrafiltration and reverse osmosis water treatment process. The state’s current clean water supply coverage is only 81.4%
[8]
. Although the Malaysia Federal and Sarawak State governments allocate funding to the SAWAS, more is needed to achieve the goal of 100% clean water supply coverage throughout the state by 2025. The cost of setting up a water treatment system can be substantially high, as it includes the cost of constructing the entire water treatment facilities and connecting them to a water distribution network.
Hence, JBLAB needs to take a different approach under the SAWAS initiative. As Sarawak is blessed with abundant rainfall, one of the ways to ensure a reliable and sustainable raw water supply to the rural community for inland areas is to install a rainwater harvesting system (RWHS) for each rural household. Rainwater can be used for potable and non-potable purposes and can also be stored as a backup supply in times of water scarcity
[9]
. This approach could assist SAWAS in achieving 100% clean water supply coverage throughout Sarawak.
For 4000 years ago, the RWHS has been introducing and delivering high-quality water for drinking and cooking
[10]
. In Malaysia, the National Hydraulic Research Institute Malaysia (NAHRIM) is actively involved in designing and installing RWHS
[11]
. The water pH collected in rural areas is around 6
[12]
[13]
. A typical RWHS is known to have 80% to 89% efficiency in capturing rainwater
[14]
[15]
. The factors affecting the reliability of RWHS are water demand, rainfall intensity, roof size, and rainwater harvesting tank size. The rain harvesting tank should be large enough to store sufficient captured rainwater to attain a higher efficiency or reliability percentage of the water supply. Other factors affecting the optimum rain harvesting tank size are climate, population, and environment.
In this study, the selected study area is Sion village, a squatter located in the Serian Division, Sarawak. There is no water supply at Sion village. Global Peace Foundation Malaysia installed the RWHS for Sion village under the Communities Unite for Purewater (CUP) programme in 2018 to provide a clean water supply to the Sion community
[16]
[17]
. The standard tank size installed was 2 m3 for each household, without considering the roof sizes and water demands. However, the optimal rainwater harvesting tank size can vary depending on the roof size and water demands. Each house in this study had a distinct roof size and water demand. Therefore, this study’s novelty focuses especially on the analysis and design of optimal RWHS tank size and its relationship with roof sizes for a squatter settlement located in the tropical region.
2. Study Area
The selected study area is Sion village, located in Tapah area, Serian Division, Sarawak, Malaysia. Sion village is located east of Beratok village
[18]
[19]
and 3 km northeast of Tapah, about 21 Miles south of Kuching city, Sarawak (refer to
Figure 1
). The settlement is made up of a variety of oddly shaped wood and brick dwellings that the villagers constructed using whatever resources they could find or afford. The gravel road towards Sion village is full of potholes and flooding in certain areas.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 1. Locality of Sion Village.
Sion villagers place less emphasis on children’s education since children are considered the family’s primary labor force. The village’s ladies will often stay at home, take care of the household chores, and grow vegetables for the family’s consumption. There are 42 households in total, with approximately 200 villagers. Most villagers are Ibans and Bidayuh, with a small percentage of mixed-parentage Chinese and Malay
[20]
. Most villagers work as laborers in Kuching, with fewer working in small-scale farming.
In the past, the Sion communities mainly relied on rainwater and a river located 300m away as their primary water source
[16]
. In recent years, the nearby river water has been severely polluted by the upstream pig and poultry farms, making it unsuitable for potable usage. Villagers began to get rashes that turned into open sores and scabs due to taking baths in the polluted river. Realizing this, Sion villagers turned to rainwater as their primary water source. Due to financial restrictions, the rainwater was collected using modified zinc pieces as a gutter, and the harvested rainwater was stored in buckets, jars, barrels, and tanks. During the drought season, some Sion villagers walk 3km daily to the market nearby to purchase drinking water, even though their average household income is only RM800 per month.
Starting in 2018, Sion villagers have improved access to clean water under the Communities Unite for Purewater (CUP) programme, initiated by Global Peace Foundation Malaysia. YTL Power sponsored this CUP project for the Social Outcome Fund in partnership with Agensi Inovasi Malaysia (AIM). CUP aims to uplift the welfare of rural and impoverished communities by providing clean water. To date, CUP has benefited over 4256 people in 21 communities across Malaysia through technical solutions that improve access to water, a filtration technology that provides clean drinking water, and provides Water, Sanitation, and Hygiene (WASH) training that increases knowledge and awareness on water management and hygiene. This project was started in February 2018 and was completed in February 2019.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 2. RWHS designed by the team from Swinburne Sarawak in 2019.
Each house that participated in the CUP programme received a water tank (as presented in
Figure 2
), water purifier, properly installed gutters, and plumbing to collect rainwater from the rooftops effectively. Using the Global Peace water purifier gives each family access to clean water for all of their household needs. In addition, a high-volume LifeStraw Community filter was also installed to provide villagers with free access to clean water (refer to
Figure 3
). This filter has the ability to remove up to 99.9999% of bacteria, viruses, and sediments from the water, making it safe to drink even without boiling
[21]
.
In this study, Tangki NAHRIM, a rain harvesting design tool, is utilized to find the optimal tank size
[22]
. This software can be downloaded for free from the official website of National Water Research Institute of Malaysia (NAHRIM). Tangki NAHRIM considers rainfall volume and pattern, roof catchment area, and water demand. Input data include daily rainfall, roof area, percentage of losses from roof runoff, daily water demand, and tank volume. The output includes total rainwater captured, daily rainwater volume delivered, system reliability, rainwater utilization percentage, storage efficiency, and the number of days without rain or with an empty tank. Manual calculations will be used to verify the software’s reliability.
Four main parameters to determine the most appropriate and optimum size of a rainwater harvesting tank: rainfall pattern, household size, catchment area, and water demand. The potential impacts of each parameter are discussed as follows:
Rainfall pattern: The rainfall pattern is essential to analyze the availability of rainwater to be stored in the rainwater harvesting storage tank for household water supply. Historical daily rainfall data for Tarat Rainfall Station from 2013 to 2023 were obtained from the Department of Irrigation & Drainage (DID) Sarawak. The rainfall data was input into TANGKI NAHRIM rainwater harvesting simulation software to determine the reliability percentage.
Household size: Household size is crucial to determine the total water demand and consumption. The quantitative survey showed that the average household size in Sion village is six persons.
Catchment area: The roof catchment area is the horizontal roof plane under the eaves. The 42 households in Sion village were grouped into five roof sizes, namely 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2. Roof runoff flow into RWHS is calculated using Equation (1).
Q = Ieff × C × A (1)
where Q is the daily runoff (L), C is the runoff coefficient, A is the roof area connected to the tank (m2), and Ieff is the daily effective rainfall (mm). Ieff is obtained using Equation (2).
Ieff = Daily rainfall − First flush (2)
First flush is essential to remove dust, bird and animal droppings, leaves, and debris from the roof surface.
Water demand volume: Questionnaires as shown in the appendix, were used to collect local water usage data. The details of the water demand in Sion village are presented in
Table 1
.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Table 1. Daily water demands per person in rural areas <xref ref-type="bibr" rid="scirp.146388-8">
[8]
</xref>.
Activities
Water Demand (L)
Drinking
4
Cooking
6
Personal hygiene
50
Laundry
20
Utensils Washing
10
House Cleaning
15
Toilet
35
Figure 4
presents the detailed steps in modeling a rainwater harvesting tank to determine the relationship among water demand, roof sizes, and optimum size of the rain harvesting tank using Tangki NAHRIM software. The standard procedures for optimizing rain harvesting tank are:
a) Insert rainfall data—Kuching rainfall data is not available in the Tangki NAHRIM rainfall station dropdown menu. Hence, rainfall data for the Kuching station will be added manually and loaded into Tangki NAHRIM software.
b) Input roof information—roof information, including size and runoff coefficient for roof material, is input into Tangki NAHRIM. The runoff coefficient for a zinc roof that installed in this study is 0.95
[23]
.
c) Input water demand information—the water demand per day for each household is required to determine the optimum tank size for each household.
d) Input first flush volume—first flush is essential for protecting the rainwater quality by isolating the contaminant-laden water, including organic and inorganic fine particles from the roof. The first flush volumes required for different roof areas are tabulated in
Table 2
.
e) Run the simulation—The final step is running the simulation, and the resulting output will present the reliability of different rainwater harvesting tank sizes.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 4. Chronology of the design process.
To investigate the relationships among water demand, roof sizes, and optimum rain harvesting tank size for rural areas in the tropical region, various graphs will be plotted. The optimum tank size will be justified according to the reliability percentage. Higher reliability indicates that the rainwater harvesting system (RWHS) can store sufficient water to meet the water demand. The developed graphs that will be used to determine the optimum tank size for rural areas in the tropical region, particularly in Borneo, are:
a) Reliability Percentage vs. Roof Area
b) Tank Size vs. Roof Area
c) Installation Cost vs. Tank Size
d) Reliability Percentage vs. Installation Cost of Various Tank and Roof Sizes
According to the World Health Organization (WHO), the Drinking-Water Quality: Small Water Supplies guideline explicitly aims for 100% reliability in small or rural systems is often impractical
[24]
. However, reliability beyond 90% often requires exponentially greater infrastructure investment, such as larger roofs, tanks and backup systems. Therefore, the targeting reliability for RWHS ranges from 80% - 89% to achieve adequate potable capacity at reasonable cost
[25]
-
[27]
.
Thereafter, a cost analysis will be conducted to determine the payback period for the optimum tank size. RWHS installation costs as a whole are regarded as an early investment. After that, the rainwater collected will be supplied continuously without any charge. By comparing the RWHS installation cost against the water tariff charged by Kuching Water Board (KWB), a payback period analysis will be carried out to calculate the return on investment (ROI) for installing the rainwater harvesting system (RWHS).
4. Results and Discussion4.1. Roof Sizes and the Reliability Percentage for Different Tank Sizes
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 5. Reliability percentage vs roof area graph.
In this study, the supply of harvested rainwater is calculated according to yield-before-spillage (YBS) algorithm. YBS algorithm is adopting an optimistic approach, where the water is expected to be drawn from the storage tank and supplied to the end users before overflowing the tank. The remaining water after usage will be stored in the tank for use in the following days
[28]
. Since a higher reliability percentage will raise the cost of installing rainwater collecting tanks, it is unnecessary to attain a 100% reliability percentage for the ideal tank size.
Figure 5
demonstrates that the tank size of 2.724 m3 achieves a 100% reliability percentage for any roof size except for the roof size of 60 m2. However, the tank size of 2.724 m3 is much more expensive than other smaller tanks. Therefore, installing 2.724 m3 of rainwater harvesting for each household in Sion village is not financially feasible.
Therefore, a more practical rain harvesting tank size should be chosen for Sion village. Results revealed that the smallest tank size of 0.682 m3 with the smallest roof size of 60 m2 could achieve a 79.49% reliability percentage. The reliability percentage is improving gradually as the roof sizes increase from 60 m2 to 200 m2, with 85.02% for 85 m2, 85.68% for 100 m2, 88.85% for 160 m2, and 90.07% for 200 m2. Similar reliability percentage increment trends were observed for tank sizes of 1.136 m3, 1.589 m3, 1.816 m3, 2.270 m3, and 2.724 m3.
The reliability percentage for the tank size of 0.682 m3 and the roof size of 60 m2 is 79.49%. With the same roof area, it was observed that the reliability percentage increased significantly for the tank size of 1.1368 m3 to 95.50%. The results show that from tank sizes of 1.136 m3 to 2.724 m3, the reliability percentages for the roof area of 60 m2 are increasing gradually until yielding 98.39% for the tank size of 2.724 m3 (refer to
Figure 5
). The results of the roof area of 85 m2, 100 m2, 160 m2, and 200 m2 revealed that all the investigated roof sizes achieved higher reliability percentages than 85%, starting from the tank size of 1.136 m3, meeting the benchmark for reliability percentage between 80% and 89%. The findings clearly demonstrated that increasing roof area and tank sizes would raise reliability percentages, leading to increased efficacy in rainwater collection to provide for the village’s water needs. Considering the available tank sizes with the corresponding reliability percentage against various roof sizes, the minimum tank size of 1.136 m3 accomplishes a reliability percentage of more than 85% at Sion village for the roof size of 60 m2. While for other roof sizes, including 85 m2, 100 m2, 160 m2, and 200 m2, a minimum tank size of 0.682 m3 is adequate to gain a reliability percentage greater than 85%.
4.2. Relationship between Tank and Roof Sizes to Achieve the Reliability Percentage
Figure 6
demonstrates the relationship between the tank and roof sizes to achieve a reliability percentage of 75%, 80%, 85%, 90%, and 95%. It was observed that for a roof size of 60 m2, a reliability percentage of 75% can be achieved with a tank size of 0.52 m3. While roof areas of 85 m2, 100 m2, 160 m2, and 200 m2, can attain reliability percentages of 75% with tanks that are in the size of 0.34 m3, 0.33 m3, 0.30 m3, and 0.30 m3, respectively. A reliability percentage of 80% can be achieved for roof sizes of 60 m2, 85 m2, 100 m2, 160 m2 and 200 m2, with the tank that is 0.74 m3, 0.50 m3, 0.40 m3, 0.33 m3, and 0.33 m3 in size, respectively. Meanwhile, roof sizes of 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2 are able to achieve 85% reliability percentage with the corresponding tank sizes of 1.07 m3, 0.67 m3, 0.65 m3, 0.59 m3 and 0.50 m3, respectively. With roof sizes of 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2, correspondingly, tank sizes of 1.61 m3, 0.97 m3, 0.97 m3, 0.90 m3, and 0.70 m3 can achieve 90% reliability rate. With tanks that are 2.20 m3, 1.60 m3, 1.40 m3, 1.28 m3, and 1.20 m3 in sizes, and corresponding roof sizes of 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2, can yield a reliability percentage of 95%. Generally, the findings illustrated that the roof and tank sizes are proportional with reliability percentage. Bigger tank sizes with larger roof areas will yield a higher reliability percentage, while smaller tank sizes with smaller roof sizes will lead to low reliability.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 6. Tank size vs. roof area graph.
4.3. Cost Analysis
RWHS costs include the materials and installation of the WEIDA Polystor HDPE water tank, gutter, water rundown pipe, etc. Generally, the polystor tank’s price is proportional to the tank size.
Table 3
presents the installation cost and payback period for different tank and roof sizes at Sion village. As the desired reliability percentage is 80% to 89%, the minimum tank size achieved 80% volumetric reliability is indicated in yellow. The payback period is the time required to get the equivalent return from the investment of constructing the RWHS system, calculated based on Equation (3).
(3)
where the cost of water saved is defined as the total volume of water supplied by RWHS X the water rate charged by Kuching Water Board (KWB).
<xref ref-type="bibr" rid="scirp.146388-"></xref>Table 3. Cost analysis for different roof areas.
Roof size
(m2)
Tank Size (m3)
Rainwater yield (L)
Reliability (%)
Price saving (RM)
Installation cost (RM)
Payback Period (Years)
60
0.682
92.85
79.49
90.00
729.03
8.1
1.136
99.86
85.50
97.00
976.53
10.1
1.589
104.74
89.67
102.00
1261.53
12.4
1.816
107.37
91.93
104.00
1336.53
12.8
2.270
111.71
95.64
108.00
1591.53
14.7
2.724
114.92
98.39
111.00
1861.53
16.7
Continued
85
0.682
99.3
85.02
96.00
812.46
8.4
1.136
107.17
91.76
104.00
1059.96
10.2
1.589
111.37
95.35
108.00
1344.96
12.5
1.816
113.29
96.99
110.00
1419.96
12.9
2.270
115.84
99.18
112.00
1674.96
14.9
2.724
116.8
100.00
113.00
1944.96
17.2
100
0.682
99.95
85.57
97.00
831.00
8.6
1.136
107.88
92.36
105.00
1078.50
10.3
1.589
111.72
95.65
108.00
1363.50
12.6
1.816
113.96
97.57
111.00
1438.50
13.0
2.270
115.84
99.18
112.00
1693.50
15.1
2.724
116.8
100.00
113.00
1963.50
17.3
160
0.682
103.77
88.84
101.00
960.78
9.5
1.136
109.41
93.67
106.00
1208.28
11.4
1.589
113.57
97.23
110.00
1493.28
13.6
1.816
114.88
98.36
111.00
1568.28
14.1
2.270
116.16
99.45
113.00
1823.28
16.2
2.724
116.8
100.00
113.00
2093.28
18.5
200
0.682
105.2
90.07
102.00
1034.94
10.1
1.136
110.4
94.52
107.00
1282.44
12.0
1.589
113.92
97.53
111.00
1567.44
14.2
1.816
115.2
98.63
112.00
1642.44
14.7
2.270
116.48
99.73
113.00
1897.44
16.8
2.724
116.8
100.00
113.00
2167.44
19.1
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 7. Installation cost vs tank size.
Figure 7
depicts the installation cost of RWHS rising as tank capacity increases. The cheapest tank size to install is 0.682 m3, while the tank with the highest installation cost is 2.724 m3. The installation cost for a 0.682 m3 tank ranges from RM729.03 to RM1034.94 for different roof sizes. The installation cost for a bigger roof area is slightly higher as it requires longer gutter to collect the rainwater water and channel them towards the rainwater harvesting tank. The cost analysis showed that the installation cost for a tank with a volume of 1.136 m3 can range from RM976.53 to RM1282.44; RM1261.53 to RM1567.44 for a tank with a volume of 1.589 m3; RM1336.53 to RM1642.44 for a tank with a volume of 1.816 m3; RM1591.53 to RM1897.44 for a tank with a volume of 2.270 m3; and finally, RM1861.53 to RM2167.44 for a tank size of 2.724 m3.
The RWHS cost vs. volumetric reliability graph for various tank sizes can be analyzed with the slope gradient, categorized into gentle and steep slopes. The steep slope illustrates that the system reliability was improved significantly by a small increment in cost. In contrast, the gentle gradient linear line reveals that the system reliability was not much improved even after investing a lot in the system.
Figures 8-12
present the percentage reliability of RWHS for roof sizes of 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2, respectively.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 8. Reliability vs installation cost of various tank sizes for roof size of 60 m<sup>2</sup>.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 9. Reliability vs installation cost of various tank sizes for roof size of 85 m<sup>2</sup>.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 10. Reliability vs installation cost of various tank sizes for roof size of 100 m<sup>2</sup>.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 11. Reliability vs. installation cost of various tank sizes for a roof size of 160 m.
<xref ref-type="bibr" rid="scirp.146388-"></xref>Figure 12. Reliability vs. installation cost of various tank sizes for a roof size of 200 m<sup>2</sup>.
Results revealed that for the roof size of 60 m2, the tank size of 0.682 m³ is only able to reach the reliability percentage of 79.49%, which is below the desirable target of 80%. However, a tank size of 1.136 m3 is able to yield reliability up to 85.5%. The total cost for RWHS installation for 1.136 m3 tank size is RM976.53. Cost analysis demonstrated that the total payback period is estimated to be 10.1 years, with a monthly water-saving cost of RM97.
For the roof sizes of 85 m2, 100 m2, 160 m2, and 200 m2, the minimum tank size of 0.682 m3 is sufficient to obtain a reliability percentage of more than 80%. With the tank size of 0.682 m3, the roof areas of 85 m2, 100 m2, 160 m2, and 200 m2 achieve the reliability percentage of 85.02%, 85.57%, 88.84%, and 90.07%, respectively. The cost analysis revealed that the total installation costs for the roof area of 85 m2, 100 m2, 160 m2, and 200 m2 are found to be RM812.46, RM831.00, RM960.78, and RM1034.94, respectively.
The payback period for the roof area of 60 m2, 85 m2, 100 m2, 160 m2, and 200 m2, and tank sizes of 0.682 m3, 1.136 m3, 1.589 m3, 1.816 m3, 2.270 m3 and 2.724 m3, ranges from 8.4 years to 10.1 years, calculated according to the residential water tariff rate of RM 0.53/m3, charged by the Kuching Water Board (KWB). However, as Sion village is not currently connected to the potable water supply grid, RHWS is the only solution to supply sustainable clean water for this squatter area. Moreover, the RHWS will provide free clean water for this village until the end of the system life span. Therefore, RWHS is feasible to be adopted in this project, and it is a sustainable way to conserve water resources for long-term consideration.
4.4. Limitation
The identification of optimal tank sizes for RWHS faces inherent uncertainties stemming from variations in rainfall, climate change, and fluctuations in demand. The natural variability in rainfall, which includes seasonal and interannual changes, can result in inaccurate assessments of water availability, thereby impacting the reliability of storage. Climate change adds complexity to the sizing process, as alterations in the intensity, frequency, and timing of precipitation may make historical rainfall data less applicable to future scenarios. Furthermore, household water demand is variable, shaped by changes in population, lifestyle modifications, and seasonal requirements. These factors collectively challenge the accuracy of sizing models and underscore the need for adaptive and flexible RWHS designs to maintain performance under changing environmental and socio-economic conditions.
5. Conclusions
This study has successfully determined the appropriate rainwater harvesting tank sizes for different roof sizes in Sion village. The optimal tank size for the roof size of 60 m2 was found to be 1.136 m3 with a reliability percentage of 85.50%. Results revealed that the minimum tank size of 0.682 m3 manufactured by WEIDA Polystor HDPE water tank is adequate to achieve the reliability percentage of more than 80% for the roof sizes of 85 m2, 100 m2, 160 m2, and 200 m2. The simulation results demonstrated that the reliability percentage achieved using the tank size of 0.682 m3 was found to be 85.02% for 85 m2 roof area, 85.57% for 100 m2 roof area, 88.84% for 160 m2 roof area, and lastly 90.07% for 200 m2 roof area.
Referring to cost analysis, the payback period for installing the optimum tank size of 1.136 m3 for 60 m2 roof area is 10.1 years. The results revealed that the minimum tank size of 0.628 m2 is adequate to store and supply water to the Sion village with the roof area of 85 m2, 100 m2, 160 m2, and 200 m2. As 0.682 m3 tank size is cheaper than other bigger tank sizes, the installation cost would be significantly reduced. The payback period for installation cost for a roof size of 85 m2 was found to be 8.4 years, followed by 8.6 years for a roof area of 100 m2, 9.5 years for a roof area of 160 m2, and lastly 10.1 years for a roof area of 200 m2. It was observed that the installation cost is proportionate to the roof area as wider and longer roof areas require longer rainwater gutters.
In this case study, the RWHS is a sustainable solution to provide hygiene and a safe water supply to the squatters in Sion village. The collected rainwater can be used for potable and non-potable purposes. The reliability percentage of 80% to 89% indicates that the RWHS can supply sufficient water to the squatters in Sion village. The cost analysis revealed that the RHWS system is affordable, with the payback period ranging from 8.4 years to 10.1 years. Meanwhile, collecting rainwater can also help reduce the flood risk that occurs in Sion village and downstream.
Declaration
We here submit the manuscript entitled “Relationship of Roof Areas and Rainwater Harvesting Tank Sizes for Squatter at Sion village, Sarawak, Borneo Island” to be considered for publication. We declare that this is our original research work.
Availability of Data and Material
Data will be made available on reasonable request.
Appendix: Survey Questionnaire
Section A: Household Information
1) How many people live in your household?
2) What is the age range of household members? (Tick all that apply)
3) How long have you been staying at your current residence?
Section B: Water Usage Patterns
For each activity below, please estimate the average daily water use per person. (If unsure, provide your best estimate.)
Activity
Approximate volume used daily (liters)
Frequency per day
1. Drinking
______ liters
______ times
2. Cooking
______ liters
______ times
3. Personal hygiene (bathing, hand washing, brushing teeth, etc.)
______ liters
______ times
4. Laundry
______ liters
______ loads/day
5. Utensil washing
______ liters
______ times
6. House cleaning (mopping, etc.)
______ liters
______ times/week
7. Toilet flushing
______ liters
______ flushes/day
Section C: Water Supply and Storage
1) What is your primary source of water?
2) Do you use any water storage system at home (e.g., water tank)?
If yes:a) What is the capacity of your water storage tank? ______ littersb) How often is it refilled? ______ times/week
References
Huang, Y.F., Ang, S.Y., Lee, K.M. and Lee, T.S. (2015) Quality of Water Resources in Malaysia. In: Research and Practices in Water Quality, InTech, 65-94. >https://doi.org/10.5772/58969.
World Bank (2004) World Development Report 2005: A Better Investment Climate for Everyone. The World Bank.
Robinson, J. (2005) Urban Geography: World Cities, or a World of Cities. Progress in Human Geography, 29, 757-765. >https://doi.org/10.1191/0309132505ph582pr
Kuok, K.K., Chiu, P.C. and Mersal, M.E. (2017) Investigation of Sarawak River Kiri Sedimentation before and after Bengoh Dam Construction. International Journal of Geology, Agriculture and Environmental Sciences, 5, 9-12.
Kuok, K.K. and Chiu, P.C. (2018) Indigenous Drinking-Water Consumption Pattern of Residents in Kuching City: Results of a Pilot Study. Journal of Water, Sanitation and Hygiene for Development, 8, 817-824. >https://doi.org/10.2166/washdev.2018.004
Kuok, K.K., Rahman, M.R., Bakri, M.K.B., Chan, C.P., Yun, C.M., Al-Bogami, A.S., et al. (2022) Sustainable Clean Water Production Using Bamboo Activated Carbon for Rural Residents in the Borneo Island. BioResources, 17, 3227-3241. >https://doi.org/10.15376/biores.17.2.3227-3241
Ministry of Utility and Telecommunication (2023) Kenyahs of Long Busang Enjoying Free Power, Water Supply Thanks to Sares, Sawas Projects. >https://mut.sarawak.gov.my/web/subpage/news_view/551
Kuok, K.K., Chiu, P.C., Rahman, M.R., Bakri, M.K.B. and Chin, M.Y. (2023) Modelling the Effects of Socio-Economic Demographics on Urban Water Usage in Kota Samarahan, Sarawak: A New Education Hub in Borneo Island. Journal of Sustainability Science and Management, 18, 102-117.
Kuok, K.K., Chiu, P.C., Rahman, M.R., Bakri, M.K.B. and Chin, M.Y. (2021) Performance of Rainwater Harvesting Systems in Institutional Buildings under Different Reliability and Future Economy Benefits. Journal of Hunan University Natural Sciences, 48, 58-66.
Fulton, L. (2018) A Simulation of Rainwater Harvesting Design and Demand-Side Controls for Large Hospitals. Sustainability, 10, Article 1659. >https://doi.org/10.3390/su10051659
Che-Ani, A., Shaari, N., Sairi, A., Zain, M. and Tahir, M. (2009) Rainwater Harvesting as an Alternative Water Supply in the Future. European Journal of Scientific Research, 34, 132-140.
Thomas, T.H. and Martinson, D.B. (2007) Roofwater Harvesting. A Handbook for Practitioners. International Water and Sanitation Centre, Technical Paper Series.
Kuok, K.K. and Bessaih, N. (2007) Artificial Neural Networks (ANNS) for Daily Rainfall Runoff Modelling. Journal of the Institution of Engineers, Malaysia, 68, 31-42.
Kuok, K.K., Harun, S., Shamsuddin, S.M. and Chiu, P.C. (2010) Evaluation of Daily Rainfall-Runoff Model Using Multilayer Perceptron and Particle Swarm Optimization Feed Forward Neural Networks. Journal of Environmental Hydrology, 18, 1-16.
Kuok, K.K. and Chiu, P.C. (2019) Space-Saving Rainwater Harvesting Tanks for Double Story Houses in Kuching, Sarawak. International Journal of Engineering&Technology, 8, 38-43.
Swinburne Sarawak (2018) Global Peace and Swinburne Collaborate on Water Project in Tapah. >https://www.swinburne.edu.my/news/global-peace-swinburne-collaborate-water-project-tapah.php
Kuok, K.K., Chiu, P.C. and Selamat, A. (2019) Comparison of Bat Neural Networks and Bat Optimisation Neural Networks for Rainfall Forecasting: Case Study for Kuching City. In: Advancing Technology Industrialization through Intelligent Software Methodologies, Tools and Techniques, IOS Press, 79-92.
Mapcarta (2021). Kampung Sion. >https://mapcarta.com/N5049904837
Kuok, K.K., Chiu, P.C., Rahman, M.R., Bakri, M.K.B. and Chin, M.Y. (2022) Effectiveness of Centralized Wastewater Treatment Plant in Removing Emerging Contaminants: A Case Study at Kuching, Malaysia. Journal of Water Resource and Protection, 14, 650-663. >https://doi.org/10.4236/jwarp.2022.149034
YTL Foundation (2020) Learn from Home—Kampung Sion. >https://www.ytlfoundation.org/november2020/
Kuok, K.K. and Chiu, P.C. (2020) Optimal Rainwater Harvesting Tank Sizing for Different Types of Residential Houses: Pilot Study in Kuching, Sarawak. Journal of Engineering Science and Technology, 15, 541-554.
Nahrim, T. (2021) Official Website of National Water Research Institute of Malaysia (NAHRIM). >https://www.nahrim.gov.my/tangki-nahrim-v1-0/
DID (2012) Urban Stormwater Management Manual for Malaysia. Department of Irrigation and Drainage Malaysia: Kuala Lumpur, Malaysia.
World Health Organization (2024). Guidelines for Drinking Water Quality: Small Water Supplies. World Health Organization. >https://iris.who.int/bitstream/handle/10665/375822/9789240088740-eng.pdf
Semaan, M. (2020) A Novel Approach to Communal Rainwater Harvesting for Single-Family Housing: A Study of Tank Size, Reliability, and Costs. Doctoral Dissertation, Virginia Polytechnic Institute and State University. >https://vtechworks.lib.vt.edu/server/api/core/bitstreams/e7b0280e-3f3f-407f-a257-70e6bd30d9c9/content
Teston, A., Piccinini Scolaro, T., Kuntz Maykot, J. and Ghisi, E. (2022) Comprehensive Environmental Assessment of Rainwater Harvesting Systems: A Literature Review. Water, 14, Article 2716. >https://doi.org/10.3390/w14172716
Suprapti, S., Kusuma, M.S.B., Kardhana, H., Cahyono, M. and Juliana, I.C. (2025) Communal-Based Domestic Rainwater Harvesting System: A Novel Approach to Alternative Solutions for Increasing Water Supply and Recharging Groundwater in Jagakarsa Urban Area, South Jakarta. Case Studies in Chemical and Environmental Engineering, 11, Article 101126. >https://doi.org/10.1016/j.cscee.2025.101126
Kuok, K.K., Chiu, P.C. and Ting, D.C.M. (2020) Evaluation of “C” Values to Head Loss and Water Pressure Due to Pipe Aging: Case Study of Uni-Central Sarawak. Journal of Water Resource and Protection, 12, 1077-1088. >https://doi.org/10.4236/jwarp.2020.1212064