Atmospheric Water Harvesting

Background:

Freshwater scarcity is one of the defining challenges of the 21st century: over two billion people live in areas experiencing high water stress, and demand continues to grow with population, urbanization, and climate change. Conventional responses are often out of reach for the communities that need water most. Groundwater, the traditional fallback, is being depleted faster than it can recharge, and in many regions — particularly arid and semi-arid areas — aquifers are simply absent, too deep, or contaminated, making drilling impossible or uneconomical. Similarly, desalination offers abundant supply only to coastal populations: it requires direct access to seawater, massive energy infrastructure, and heavy capital investment, leaving inland and remote regions with no realistic path to benefit. In this context, atmospheric water harvesting (AWH) — extracting water directly from the air via fog collection, dew condensation, or sorbent-based systems — emerges as a compelling and flexible alternative. The atmosphere holds an estimated 12,900 cubic kilometers of water at any given time, a resource available virtually everywhere on Earth, independent of rivers, aquifers, or coastlines. While AWH is not yet a replacement for large-scale infrastructure, it can provide decentralized, off-grid water production precisely where other options fail — making it not merely a convenience, but in many settings a necessity. This challenge invites students to design, build, and evaluate innovative AWH solutions that turn the air itself into a viable water source.

Problem statement:
Atmospheric water harvesting is fundamentally constrained by local climate: the amount of water recoverable from air depends directly on its temperature and relative humidity. In hot, humid climates, condensation-based systems (dehumidification, dewing) perform well, but in hot, arid climates the air is often too dry for conventional cooling approaches to be viable — here, sorbent-based systems (desiccants, metal-organic frameworks, hygroscopic salts) that capture moisture even at low humidity become the only realistic option, at the cost of added system complexity and a regeneration step. In cold climates, frost formation, freezing of collected water, and low absolute humidity impose entirely different design requirements, while coastal fog-prone regions favor passive fog collection that would be useless inland. The core problem is therefore twofold: no single AWH technology works across all weather conditions, and each technology's yield is highly sensitive to daily and seasonal fluctuations it cannot control.

The second defining constraint is energy consumption. Cooling air below its dew point, heating sorbents to release captured water, or forcing air through collectors all demand significant energy — often more per liter than the water is worth in remote or off-grid contexts. This is precisely where the opportunity lies: AWH does not need to operate as a standalone system. Waste heat recovery from industrial processes, data centers, power generation, or even solar-thermal installations can drive sorbent regeneration at near-zero marginal energy cost. Similarly, excess or off-peak electricity, cold streams from LNG regasification, and nocturnal radiative cooling can power condensation pathways. Designing AWH systems that couple synergistically with existing energy flows — rather than compete for dedicated energy supply — is the key to making atmospheric water economically and environmentally viable.

The challenge:

When crisis strikes — conflict displacing populations into refugee camps, earthquakes, floods, or droughts devastating a region — access to safe water and energy collapses simultaneously. Displaced populations concentrate in locations chosen for safety, not resource availability: arid borderlands, deforested terrain, or areas where wells are absent, contaminated, or destroyed. Trucking water in is expensive, slow, and vulnerable to supply-chain disruption; desalination is irrelevant inland; and damaged or nonexistent grid infrastructure means energy must be generated locally, often with limited fuel supply. In these settings, atmospheric water harvesting (AWH) — extracting water from the air itself — becomes not a flexibility option but a lifeline: a decentralized source that requires no existing infrastructure, no groundwater, and no surface water, deployable wherever the displaced population actually is.
Yet designing AWH for crisis conditions is exceptionally demanding. The system must cope with the specific weather of the crisis site — hot and humid monsoon flood zones, cold winter refugee camps, or hot-arid desert settlements where conventional dewing fails and sorbent-based capture is required — while remaining robust to daily and seasonal variation it cannot control. It must minimize energy consumption, since energy is scarce and competing with medical services, lighting, and communications; the strongest designs will therefore exploit synergies with available energy flows — waste heat from generators or field kitchens, solar-thermal heat for sorbent regeneration, off-peak or surplus power, or fully passive pathways such as radiative cooling and fog collection. And beyond climate and energy, crisis deployment imposes its own hard constraints: rapid deployability, transportability, resilience to dust and mishandling, operation without skilled personnel, and water quality assurance for a vulnerable, protected population.