From mechanism to deployment: Hydrogel-based solar, atmospheric, and fog water capturing technologies

Freshwater scarcity driven by climate variability, population growth, and uneven infrastructure is accelerating the need for decentralized water capturing technologies (WCT). Hydrogel-based materials have emerged as versatile platforms for three complementary pathways: solar steam generation (SSG) for desalination, sorption-driven atmospheric water harvesting (AWH), and surface-engineered fog capture (FC). Although numerous hydrogel formulations have been reported, performance metrics vary widely due to inconsistent testing conditions and limited long-term validation, complicating meaningful comparison and practical assessment. This review adopts a unified, mechanism-oriented framework to analyze hydrogel-enabled water capture. We examine how water-state regulation, hierarchical transport architecture, and surface interactions collectively govern heat and mass transfer across SSG, AWH, and FC systems. Rather than focusing only on laboratory performance, we extract frequent functional strategies, identify design trade-offs between sorption strength and regeneration, thermal localization and salt stability, and adhesion versus drainage control, and clarify ongoing discussions regarding evaporation thermodynamics. In addition, we discuss manufacturing scalability, cost-reporting limitations, and system-level integration required for real-world implementation. Finally, we synthesize durability mechanisms, including salt crystallization, microbial growth, UV exposure, mechanical fatigue, and additive migration, and propose standardized laboratory and field reporting parameters to improve reproducibility. By linking polymer design principles to application-specific constraints, this review provides a comparative and application-oriented roadmap for advancing hydrogel-based WCT. • A unified, mechanism-oriented framework is used to analyze hydrogel-enabled water capture technologies. • Hybrid and biomass-based hydrogels are included. • Design trade-offs for production and application-specific functionality are broadly evaluated. • A comparative and application-oriented roadmap for advancing hydrogel-based WCT is provided.