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Global water shortages remain a significant problem worldwide due to population growth and climate change resulting in seasonal droughts. To provide a sustainable water supply for potable and non-potable uses, rainwater harvesting has received considerable attention in recent years. However, several constraints, such as microbial contaminations detected in rainwater by many studies, limit the use for drinking. Recently, researchers have had an enormous interest in harvested rainwater’s microbiological quality, evidenced by the upsurge in annual publications. Therefore this study examines the research landscape of the microbiological quality of harvested rainwater by conducting a comprehensive bibliometric analysis of the top 100 most-cited articles, most relevant countries, authors, keywords, thematic focus and trend topics over the past two decades using the bibliometrix R-package software. The results from this study indicate that the first paper with the most citations, 191, was published in 2007 by researchers from Greece. South Africa (25), Australia (20) and the USA (11) have contributed 56% of the most-cited articles. Likewise, the most prolific authors are from these countries. Sustainable treatment options for rainwater are the current research trends. These findings are relevant to current and future researchers in understanding the current state of this research area and defining their research focus.