Rainwater collecting is now a recurrent topic in urban building as part of sustainable practices. The user who wants to profit from such a practice is concerned about the economic feasibility of constructing a system capable of collecting, treating, and distributing rainwater for residential purposes. To that aim, twelve single-family homes in Belém, Pará, Brazil, were chosen for this study, each with a distinct building quality. For each home, a design and budget for the installation of a rainwater collecting system were created. Using rainwater harvesting modeling software, the hydrological performance and economic viability were assessed under various consumption and economic policy scenarios. The primary finding is that rainwater systems, independent of catchment area size, are more economically viable in homes with greater water demands. The cost of installing rainwater systems varies slightly depending on the building quality of the home where it is placed. In any situation when water usage is below the social tariff or a fixed price water bill is received, the tariff system renders rainwater harvesting economically impossible. The economic viability of rainwater collecting is improved by a combination of increasing water prices to the same level as water production costs and lower implementation costs.