Solar‐Driven Bifunctional Adsorption‐Storage Films for Ultra‐Fast Dehumidification and Freshwater Supply in Low‐carbon Buildings

ABSTRACT Indoor humidity strongly affects both building energy demand and occupant health in hot and humid climates, but it remains largely controlled by energy‐intensive mechanical systems and is seldom exploited as a source of freshwater. Here, we demonstrate a passive humidity regulation and freshwater harvesting strategy enabled by cost‐effective adsorption films (18.79$·m −2 ) that couple moisture capture, storage, and release within indoor environments. The films rapidly reduce relative humidity from 90.7% to 21.6% within one hour while maintaining long‐term operational stability and release the captured moisture to produce freshwater at a rate of approximately 1.1 kg·m −2 ·day −1 under ambient conditions. Leveraging the harvested water, an autonomous plant irrigation system is achieved, enabling sustained regulation of indoor CO 2 concentration (about 920.2 ppm) without manual intervention. Global‐scale projections indicate that this passive approach could reduce building energy consumption by up to 29.9 kWh·year −1 ·m −2 and associated carbon emissions by 16.5 kg·year −1 ·m −2 , with an exceptionally short payback period of 48 days. This work reframes indoor humidity from a latent load to a recoverable resource, offering an integrated route towards water harvesting, energy reduction and healthier indoor environments in sustainable buildings.