The aim of this investigation was an assessment of the application effectiveness of three alternatives for rainwater harvesting systems for individual households, in central Great Poland climatic conditions. During the study the amount of storm water, which can be collected from the 3 different size roof areas (80, 135, 185 m²) was assessed, in relation to the needs of a four-person family, for the region of the Tarnowo Podgórne. The receivable amount of rainwater was analysed at a rate of 10, 25, 50% of total annual precipitation occurrence probability, including the lower values, appeared in the period of 1960-2008. For the financial efficiency evaluation of investment, an indicator of the average annual cost per unit (W_s) and the net present value (NPV) were used. The results show that for the Great Poland region with the average annual sum of precipitation of 550mm, only the roof surfaces of 185 m² and bigger allow obtaining the profits from collected rainwater and reimbursement for building rainwater harvesting installations within 30 years of its operation.