This article presents a literature review on rainwater usage in buildings in Brazil. It focuses on economic, environmental and social impacts. The legislation related to rainwater harvesting—including the cities that have made such a practice mandatory—was also assessed. The literature review was based on a search strategy that uses protocols to find and select studies about the main subject, i.e., rainwater harvesting in buildings. The protocols were defined as the site to be investigated (buildings), the intervention (rainwater harvesting), and the expected result (influence on the potable water consumption). Despite the variation of water availability in the country, it was concluded that there is a high potential for potable water savings when using rainwater in buildings in Brazil. Finally, it was observed the need for financial investments in experimental research and innovation technologies in order to improve rainwater management.