The use of rainwater is widely recognized as a dependable solution to reduce and mitigate the effects of water scarcity. Research on rainwater harvesting systems has increased significantly in recent years, especially on methods and treatment systems. A rainwater harvesting system can be described as collecting and storing rainwater that can be used rather than waste as runoff. A rainwater collection system might lessen the reliance on the public water supply. This study aims to determine the suitability of a rainwater harvesting system at a double-story house, thus identifying the suitable tank size for installation. This study’s analysis used the Tangki NAHRIM 2.0 with localized input data such as rainfall, suitable roof area, and roof runoff coefficient. Findings from this study indicate that installing the rainwater harvesting system at a double-story house is suitable, and the optimum tank size is 3m3 by considering all the activities that contribute to water usage. Concisely, installing a rainwater harvesting system can reduce the monthly water bill and minimize the usage of treated water, thus preventing water scarcity in the future.

• Allen, J., & Haarhoff, J. (2015). A proposal for the probabilistic sizing of rainwater tanks for constant demand. Journal of the South African Institution of Civil Engineering, 57(2), 22-27. https://doi.org/10.17159/23098775/2015/v57n2a3

• Bakar, M. A. A., Ariff, N. M., Jemain, A. A., & Nadzir, M. S. M. (2020). Cluster analysis of hourly rainfalls using storm indices in Peninsular Malaysia. Journal of Hydrologic Engineering, 25(7), 1-11. https://doi.org/10.1061/(ASCE)HE.1943-5584.0001942

• Boretti, A., & Rosa, L. (2019). Water demand by 2050. Reassessing the Projections of the World Water Development Report. https://www.nature.com/articles/s41545-019-0039-9

• Campisano, A., Butler, D., Ward, S., Burns, M. J., Friedler, E., DeBusk, K., Fisher-Jeffes, L. N., Ghisi, E., Rahman, A., Furumai, H., & Han, M. (2017). Urban rainwater harvesting systems: research, implementation and future perspectives. Water Research, 115, 195-209.

• Chang, W., Cheng, J., Allaire, J. J., Xie, Y., & McPherson, J. (2019). Shiny: Web Application Framework for R. https://CRAN.R-project.org/package=shiny

• Daud, N. M., Mahiran, N. N., Ruslan, A. K., Hamzah, N., Bakar, A. A. A., Badrealam, S., Manan, E. A., & Hamzah, A. F. (2021). Effect of roof size on the rainwater harvesting tank sizes and performances using Tangki NAHRIM 2.0. In IOP Conference Series: Earth and Environmental Science (Vol. 920, No. 1, p. 012035). IOP Publishing. https://doi.org/10.1088/1755-1315/920/1/012035

• Department of Statistics Malaysia. (2014). Characteristics of Household 2010. https://www.mycensus.gov.my/index.php/census-product/publication/census-2010/685-characteristic-of-household-2010

• Goh, Y. C., & Ideris, M. (2021). Tangki NAHRIM 2.0: An R-based water balance model for rainwater harvesting tank sizing application. Water Practice & Technology, 16(1), 182-195. https://doi.org/10.2166/wpt.2020.106

• Hajani, E., & Rahman, A. (2014). Reliability and cost analysis of a rainwater harvesting system in peri-urban regions of Greater Sydney, Australia. Water, 6(4), 945-960. https://doi.org/10.3390/w6040945

• Jenkins, D., Pearson, F., Moore, E., Kim, S. J., & Valentine, R. (1978). Feasibility of rainwater collection systems in California [Final Technical Report]. Water Resources Centre, University of California. https://ntrl.ntis.gov/NTRL/dashboard/searchResults/titleDetail/PB288378.xhtml

• Khan, S. T., Baksh, A. A., Papon, M. T. I., & Ali, M. A. (2017). Rainwater harvesting system: An approach for optimum tank size design and assessment of efficiency. International Journal of Environmental Science and Development, 8(1), 37-43 https://doi.org/10.18178/ijesd.2017.8.1.917

• Kummu, M., Guillaume, J. H. A., de Moel, H., Eisner, S., Flörke, M., Porkka, M., Siebert, S., Veldkamp, T. I. E., & Ward, P. J. (2016). The world’s road to water scarcity: Shortage and stress in the 20th century and pathways towards sustainability. Scientific Reports, 6(1), Article 38495. https://doi.org/10.1038/srep38495

• Lani, N. H. M., Yusop, Z., & Syafiuddin, A. (2018). A review of rainwater harvesting in Malaysia: Prospects and challenges. Water, 10(4), Article 506. https://doi.org/10.3390/w10040506

• Liaw, C. H., & Tsai, Y. L. (2004). Optimum storage volume of rooftop rainwater harvesting systems for domestic use. Journal of the American Water Resources Association, 40(4), 901-912. https://doi.org/10.1111/j.1752-1688.2004.tb01054.x

• Mitchell, V. G. (2007). How important is the selection of computational analysis method to the accuracy of rainwater tank behaviour modelling? Hydrological Processes: An International Journal, 21(21), 2850-2861. https://doi.org/10.1002/hyp.6499

• Nandargi, S., & Mulye, S. S. (2012). Relationships between rainy days, mean daily intensity, and seasonal rainfall over the Koyna catchment during 1961–2005. The Scientific World Journal, 2012, 1-10. https://doi.org/10.1100/2012/894313

• Nguyen, V. M., Icikawa, Y., & Ishidaira, H. (2018). Exploring optimal tank size for rainwater harvesting systems in Asian tropical climates. Hydrological Research Letters, 12(1), 1-6. https://doi.org/10.3178/hrl.12.1

• R Core Team. (2013). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org/

• Rahman, H. (2014). Water shortage in Malaysia: Again? International Journal of Recent Trends in Engineering and Research, 4(1), 319-322. https://doi.org/10.23883/ijrter.2018.4038.8jr8f

• Struck, S. (2011). Rainwater Harvesting for Non-potable Use and Evidence of Risk Posed to Human Health Background: General Hazards found in Rainwater. https://www.ccnse.ca/sites/default/files/BCCDC-Rainwater_Harvesting_Oct_2011.pdf

• UN Report. (2018). UN World Water Development Report. https://www.unwater.org/publications/world-water-development-report-2018