<p>The intensifying effects of climate change on global water scarcity require ensuring reliable, equitable, and sustainable water supply, with novel technologies becoming increasingly central to adaptation. In this study, we develop projections of wastewater treatment and desalination capacities and analyze their associated energy demand and CO₂ emissions. While technologically mature and rapidly expanding, their future development remains underexamined as a risk of maladaptation that stems from their high energy demand and potential emissions footprint. We find that, compared to the present day, wastewater treatment and desalination capacities could double and triple, respectively, by 2050, followed by scenario-dependent multi-fold increases in energy demand and emissions. While the emissions footprint is non-negligible, it is only about a half of the projected increases in key energy-intensive adaptation options such as air conditioning. We find that water-stressed regions like Africa and South Asia, currently minor contributors to global wastewater treatment and desalination capacity, are projected to become largest producers of novel water in the second half of the century across the tested scenarios. Wastewater treatment and desalination emerge from this analysis as indispensable yet imperfect adaptation options, whose future contributions crucially depend on how their expansion is embedded in broader water and energy systems.</p>