A Spatial Life Cycle Cost Comparison of Residential Greywater and Rainwater Harvesting Systems

Decentralized, household water systems have been increasingly integrated into the centralized urban water networks to address challenges related to water stress and shortage, sustainable water production, and network resilience. However, our understanding regarding how different geospatial, housing type, and climate conditions can potentially influence the economic and water-saving benefits of different decentralized water systems remains limited. This study combined system dynamics modeling with life cycle cost assessment to investigate the payback time and water-saving benefits of household greywater recycling (GWR) and rainwater harvesting (RWH) systems in a typical single family and a typical multifamily house across 12 different cities within the United States. We found that for GWR systems, cities had optimum tank sizes of 2-3 m(3) for multifamily housing and 0.75-0.85 m(3) for single-family housing. Optimal tank sizes for RWH ranged from 5 to 10 m(3) for multifamily housing and 4-6 m(3) for single-family housing. Percent demand met for GWR systems ranged from 70% to 90% of the designated nonpotable usages, whereas RWH systems ranged from 50% to 70% across all cities. When the tank size is optimized for payback time, the percent demand met is generally 10% lower than the highest achievable demand met. This indicates a tradeoff between sizing for minimized payback time or maximized demand met. Overall, Boston, Seattle, and Atlanta performed the best in terms of payback time and demand met regardless of housing and system types.

Automated summary

The study combined system dynamics modeling with life cycle cost assessment to investigate the economic and water-saving benefits of household greywater recycling and rainwater harvesting systems in different cities across the United States. It found optimal tank sizes and demand met percentages for different decentralized water systems, indicating a tradeoff between sizing for minimized payback time or maximized demand met. Boston, Seattle, and Atlanta performed the best in terms of payback time and demand met regardless of housing and system types.