Future trends of desalination and wastewater treatment accounting for risks of maladaptation

The intensifying effects of climate change on global water stress calls for novel strategies to ensure reliable, equitable, and sustainable water supply. As population growth, urbanization, economic activities and overuse of conventional freshwater sources put pressures on water systems, novel technologies are becoming increasingly central to adaptation strategies. In this study, we provide a global assessment of the evolution and future prospects of wastewater and desalination treatment, as critical yet contested options to enhance water security. While technologically mature and rapidly expanding, their future development remains underexamined as a potential source of maladaptation due to its high energy demand and potential carbon footprint. In this study, historical data on capacities of wastewater treatment and key desalination technologies were combined with climate and socioeconomic indicators to analyze historical growth patterns and project future trajectories under different Shared Socioeconomic Pathway (SSP) scenarios. We present novel projections of wastewater treatment and desalination capacities, energy demands and CO ₂ emissions. We find that water-stressed regions like Africa and South Asia – currently only minor contributors to the global wastewater treatment and desalination capacity – are projected to become largest producers of novel water in the second half of the century across all assessed scenarios. Wastewater treatment and desalination emerge from this analysis as indispensable yet imperfect adaptation options, whose future contributions will crucially depend on how their expansion is powered and embedded in broader water and energy systems. While the emissions footprint is non-negligible, it is modest compared to other industrial emitters or projected increases in other key adaptation options such as air conditioning.