Sustainability analysis and life-cycle ecological impacts of rainwater harvesting systems using holistic analysis and a modified eco-efficiency framework

Background/Question/Methods  A sustainability paradigm is being recognized globally as a path forward for human prosperity and ecological health in the face of climate change and meeting challenges of the water-energy-food nexus. Rainfall shortages for drinking water and crop production occur throughout the world, and rainwater harvesting (RWH) contributes to water resource sustainability by offsetting surface and ground water consumption and by reducing environmental and human health impacts compared to conventional sources. RWH and related green infrastructure practices provide potential benefits that include reduced environmental and human health impacts, reduced stormwater runoff and combined sewer overflows, and enhanced ecosystem services. However, these improvements, even when considered green, must be evaluated for their impacts to ecological health, including eutrophication, global warming potential, and ecotoxicity. We present findings from recent studies that utilized life cycle assessment (LCA), life cycle cost and impact assessment to evaluate domestic, agricultural and commercial RWH systems compared with municipal water supply and irrigation. We also present a modified eco-efficiency framework and methodology for evaluating the sustainability of RWH design configurations. Subjectivity and sensitivity analysis were addressed by evaluating 10 weighting schemes and derived thresholds, revealing the least to most sustainable design options.

Results/Conclusions  LCA of commercial RWH showed that the benchmark commercial RWH system outperformed municipal water supply in all categories except ozone depletion in Washington, D.C., and the sensitivity analysis revealed pump material and pumping energy to be key components for most impact categories with conditional impact tradeoffs. The contribution of pump materials, pump energy and tank material was noted for a majority of impacts discovered across RWH systems. Our modified eco-efficiency framework included four economic, 11 environmental, and three social indicators, and we used six indicators to analyze RWH designs as decision management objectives. In three watersheds within the Albemarle-Pamlico river basin (southeastern U.S.), impact assessment categories included energy demand, fossil fuel, metals, ozone depletion, global warming, acidification, smog, blue and green water use, ecotoxicity, eutrophication, and human health effects. A watershed-wide RWH adoption rate of 25% has a number of ecological and human health benefits including blue water use reduction ranging from 2-39 Mm³, cumulative energy savings of 12-210 TJ, and reduced global warming potential of 600-10,100 Mg CO₂ eq. Potential maximum lifetime energy cost savings were estimated at $5M and $24M corresponding to domestic RWH in Greens Mill and agricultural RWH in Back Creek watersheds.