Modular life cycle assessment approach: Environmental impact of rainwater harvesting systems in urban water systems

The environmental assessment of urban water systems through life cycle analysis can be facilitated by using a modular approach. This study aimed to use such an approach to assess the impact of implementing rainwater harvesting systems in buildings in the urban environment during their lifespan, from manufacture to disposal. For this purpose, urban systems were divided into components (water treatment plant, potable water distribution, consumer water use, wastewater collection and wastewater treatment plant). The impacts were quantified using the ReCiPe 2016 H impact assessment method, which considers eighteen impact categories. A case study was carried out in the Belém river basin in central Curitiba, southern Brazil, to validate the method. The results showed a reduction of environmental impacts of up to 23.0 % on water treatment plants, up to 19.0 % on potable water distribution and up to 11.3 % on wastewater treatment plants with the implementation of rainwater harvesting systems. The consumer component was the most significant contributor in eight and seven impact categories in the scenarios with and without rainwater harvesting, respectively. Despite the increased infrastructure materials, the results showed potential for environmental impact reduction with rainwater harvesting, mainly in urban water systems' operation process (energy and chemicals consumption). By analysing the total impacts, implementing rainwater harvesting reduced the impacts in eleven out of eighteen impact categories analysed (up to 11.0 % reduction). The principal reductions occurred in ozone depletion, ionising radiation and water use. Finally, the modular life cycle assessment approach proved to be a comprehensive analysis, which can aid in the analysis and decision-making for different scenarios.