Rainwater harvesting (RWH) systems are increasingly being used as an alternative source of water supply. However, their installation is not often financially feasible. The feasibility analysis of such investments is carried out by traditional techniques that have uncertainty limitations. Thus, the objective of this study is to describe how the studies concerning the economic feasibility of RWH systems have been conducted, thus identifying trends of current studies through a systematic review. We performed a literature search of published articles and, using defined inclusion criteria, 30 relevant articles were selected. We noted an increase in publications on this issue in recent years, and we demonstrate that the feasibility of the systems is frequently calculated by discounted cash flow methods. Several studies seek to incorporate uncertainties with an analysis of sensitivity, and only one study uses real options analysis. With these analyses, we provide recommendations for future studies and an overview of the current literature.