Rainwater harvesting is a promising technique for more rational water use. However, its sustainability merits remain a subject of ongoing debate among researchers. Life cycle assessment (LCA), a method employed to measure the environmental impact of varying solutions, is helpful in this regard. Accordingly, this paper delivers an integrative review based on the PRISMA protocol, outlining challenges and potential avenues for the LCA application to rainwater harvesting. The central findings indicate that while residential buildings are most commonly examined, more consensus is needed on a uniform analytical framework. Furthermore, several benefits of rainwater are often not considered in LCA and need further exploration to understand possible synergies for its broader implementation. Finally, LCA integration with a life cycle cost assessment (LCCA) shows exciting results as it may be a more straightforward showcase of the benefits of an integrated assessment. It is concluded that specific details of the LCA of rainwater harvesting may still be simplistic. There is much work to be done in holistic assessments to prove the system’s sustainability.

Extensive implementation of rainwater harvesting (RWH) systems can promote substantial improvement in urban water resource management. Therefore, establishing the financial feasibility of RWH systems is imperative for their dissemination. This study evaluated the influence of rainfall time series indicators (average annual rainfall, seasonality index and behaviour of periods without precipitation) and design variables (catchment area, rainwater demand, number of inhabitants, potable water demand and rainwater tank size) on the financial feasibility of RWH systems in eight Brazilian cities. Correlations between rainfall indicators and financial feasibility were introduced, along with sensitivity analysis of design variables. Financial feasibility was obtained in 30% to 70% of the simulated scenarios. Initial investment and operating costs varied significantly among the eight cities according to local prices. Systems with a catchment area of 200 m² were capable of supplying, on average, 90.5% of the maximum rainwater consumption observed in this study. Local variation of potable water tariff schemes affected the financial feasibility of RWH systems. The number of inhabitants was the most influential design variable on the financial feasibility of RWH systems, followed by the rainwater tank size. Places with lower rainfall seasonality indexes and lower incidence and duration of dry periods are likely to lead to greater financial feasibility.

Rainwater harvesting (RWH) systems are key solutions to improve water resource management in cities, and financial feasibility is essential for their diffusion. Moreover, studies about rainwater often adopt diverse design approaches, leading to incompatible results for direct comparison. This study introduces a categorised item-by-item outlay procedure and evaluates indirect (gravity) and direct (pressuriser) rainwater distribution schemes. Computer simulations were used to design 54 generic RWH system scenarios in Maringá based on a range of design variables. For each scenario, a monthly cost–benefit balance was built, and discounted payback, net present value, and internal rate of return were obtained. Similar outlays were obtained for direct and indirect rainwater distribution schemes (∆ = BRL 21.81) with an average of BRL 13,484.87 among all scenarios. Average operational costs were estimated at BRL 1.31/month.m³ of rainwater demand. On average, paybacks of 14.7 years and internal rates of return of 0.99% per month were obtained among feasible scenarios. Like in other studies, financial feasibility indicators presented significant correlations (0.88 ≤ R² ≤ 0.94) with rainwater demand. The initial outlay distribution proposed herein provides an objective reference for result comparison among similar studies. Similar results for both rainwater distribution schemes point towards investigating alternative technical solutions for RWH systems.