Cost-effective rainwater harvesting system in the Metropolitan Area of Barcelona

Expected population growth will result in increasing water demand. The consequences could potentially jeopardise water resource availability especially in urban areas and significantly increase costs. Rainwater harvesting (RWH) systems can aid not only in meeting water demand partially, but also doing so in a more cost-effective and environmentally friendly manner than other techniques. Although the reduction of environmental burdens is fairly obvious, the question for urban planners and consumers remains: are RWH systems economically feasible? This paper investigates cost-effectiveness of eight different scenarios in the Metropolitan Area of Barcelona. To do so, monetary investment is quantified to provide rainwater for laundry purposes. Results indicate that high density scenarios are financially the most suitable choices (higher net present value and shorter payback time) given that: more users mean more savings from laundry additive consumption. Further studies should consider which are the variables that have a greater effect on the financial appraisal. Similar to inflation rate, specific attention should be paid to the costs associated with the storage tank location. Included on the savings side should be the no tap water consumption effect on the water bill, along with special attention to tap water prices in the area of study.