An Inventory Comparison of Harvesting Rainwater from Roofs and Stormwater from Pervious Pavements

The use of pervious pavements is widely researched, and the literature proves they have many benefits, including the possibility of harvesting stormwater for use in buildings. However, despite much research, few studies discuss the differences between this approach and rainwater harvesting through roofs. Thus, this study aims to assess different rainwater harvesting models, i.e. with and without pervious pavements, through water balance simulations. A university building in the Federal University of Santa Catarina (UFSC) was chosen for the case study, and six water supply, paving, and drainage scenarios were modelled. The first scenario was considered the base case, with impervious paving and water supply only by the local utility. The other scenarios considered combinations of rainwater harvesting from roofs and pavements and the variation of the pervious surface in two types, i.e. made of asphalt and Portland cement materials. Another water balance model was also assessed for pervious pavements, providing the pavement’s hydraulic performance and designed cross-section. Considering all harvesting scenarios, results showed a potable water savings potential of 62 to 65%, with a yearly reduction of approximately 1400 to 1450 m³ of water. Other benefits from the use phase were also assessed, with a possible reduction of almost 200 tons of carbon (CO2) in Portland cement pavements. Better water quality was also provided, with a reduction of approximately 250, 7 and 43 kg of, respectively, phosphorus, nitrogen, and zinc for asphaltic and concrete pervious pavements. Finally, one observes many differences in material demand for rainwater and stormwater models, such as different amounts of concrete, polyethylene, reinforcement steel, gravel, and other materials. This inventory is intended to amplify decision-making strategies in such systems.