This research evaluates which is the most cost-efficient rainwater harvesting (RWH) system in a new commercial building located in the north of Portugal, in Braga. Based on the economic analysis, the cost-efficiency of the presented RWH strategies may be considered for the case studied. The results of this research indicate that RWH scenarios proposed are cost-efficient. Considering a 10 % discount rate, the water price charge in the municipally of Braga and the cost of the infrastructures would be enough to make RWH cost-efficient for this option. At this discount rate, the payback period ranges from 2 to 6 years and the internal rate of return would range from 23 to 76 %. If a discount rate of 5 % were considered, the payback periods would be reduced by approximately 1 year.