Global Potential of Potable Reuse as a Water Scarcity Solution Across Coupled Climate and Socioeconomic Future

Urban water systems worldwide face escalating scarcity challenges driven by the combined pressures of climate change and socioeconomic development. Population growth and urbanization are concentrating water demand in cities, while climate variability and extremes increasingly threaten reliable supply. Simultaneously, competing demands for human activities and ecosystems functioning intensify pressure on finite freshwater resources, making conventional supply strategies insufficient in many regions.

Potable water reuse (PR), the process of treating and recycling wastewater to produce an alternative source of drinking water, is one promising solution to mitigating urban water scarcity. Here, we quantify the global potential of municipal PR as a water scarcity mitigation strategy and explore how its effects vary across development levels and governance contexts. We use the Global Change Analysis Model (GCAM), an integrated multi-sectoral model capturing long-term interactions between economy, climate, water, energy, and land systems, to assess PR potential within coupled socioeconomic and resource systems. We systematically generate a comprehensive scenario ensemble using combinatorial experimental design, simultaneously examining six key drivers related to water supply, demand, and allocation rules. This exploratory modeling framework enables comprehensive assessment of deep uncertainty while identifying critical factor combinations and threshold conditions where PR delivers improved water security outcomes across 235 global water basins.

Preliminary results highlight that PR can significantly reduce freshwater withdrawals, buffer urban demand during shortages, and indirectly relieve pressure on agricultural systems.  However, our analysis reveals substantial spatial heterogeneity in PR effectiveness. Development level and governance capacity strongly mediate implementation potential, creating clear patterns of implementation inequality i.e. regions with greatest water stress often face the steepest barriers to adoption. Critically, our findings underscore that PR is best viewed as a complementary tool within a broader portfolio alongside conservation, desalination, and improved allocation mechanisms rather than a standalone solution.