摘要：This paper introduces a proposal for reservoir volume calculation in rainwater harvesting systems. The proposed method can be used for reservoir volume design in rainwater harvesting systems and is based on three important variables. These variables are water demand, system efficiency and repayment time. Several simulations were carried out in different scenarios considering typical values of both catchment area （for low-income and medium-income households） and water demand, with fixed water and tank costs. Results showed that the integrated analysis of demand, efficiency and repayment time may assist designers to determine a more adequate reservoir volume.