A comparison of environmental impacts between rainwater harvesting and rain garden scenarios

Rain garden (RG) is a simple alternative to reduce pollutant loads carried through runoff. However, RG construction impacts the environment, where it demands evidence of net benefits generated once commissioned for operation. This study has simulated the reduction of runoff and pollutant loads due to the installation of RGs. Consequently, the reduction of the impacts on the environment was estimated using the LCA method. A comparison was carried out between the scenarios with and without RG with the most feasible (environmentally) rainwater harvesting (RWH) system. Three RG sizes are considered, such as 3, 4, and 6 m2 in dry, average, and wet annual rainfall conditions. The catchment-scale results showed that the runoff generation impacts of the RGs' operation phase were about (24–54%), (21–49%), (21–47%), and (14–45%) of the system without RG on eutrophication, human toxicity-carcinogenic, ecotoxicity-freshwater, and ecotoxicity-marine, respectively. However, once fabrication & installation were added, RG had much higher net impacts than without RG, except for eutrophication and ecotoxicity-freshwater. Hence, the net ecotoxicity-freshwater impact was lower for all scenarios except 4 and 6 m2 RG sizes during dry rainfall conditions. The most feasible RWH scenarios (e.g., 2000 & 3000 L tanks) had net impacts of 3–81% of the RG systems on global warming, human toxicity-carcinogenic, and ecotoxicity-terrestrial categories. On the other hand, RWH had net impacts of 105–200% on ozone depletion and eutrophication and 51–119% on the ecotoxicity-freshwater and ecotoxicity-marine of the RG systems.