Researchers in Saudi Arabia develop a passive atmospheric water harvesting system designed for arid environments, improving condensation efficiency without electricity.
Atmospheric water harvesting redesigned for desert climates
Passive atmospheric water harvesting systems are advancing rapidly as water scarcity intensifies across many regions of the world. The latest innovation comes from engineers at King Abdullah University of Science and Technology (KAUST), led by Professor Qiaoqiang Gan.
The team has developed a new humidity collection system capable of operating efficiently in arid climates such as Saudi Arabia, enhancing passive water recovery through improved radiative cooling and gravity-assisted condensation.
How passive atmospheric water harvesting works
Passive atmospheric water harvesting systems capture and condense moisture from the air without requiring electricity.
Currently, these technologies fall into two main categories:
- Absorption-based systems use materials such as metal-organic frameworks, silica gel or zeolites. These systems typically operate during the day and can function even at low relative humidity. Once the absorbent material becomes saturated, the system is exposed to sunlight. Heat causes the water to evaporate, condense on interior surfaces and then be collected.
- Dew harvesting systems rely on radiative cooling surfaces and require higher relative humidity. These devices emit thermal radiation within the atmospheric transparency window, between 8 and 13 micrometers, effectively releasing heat as infrared radiation into space. This radiative effect cools the surface below the dew point, causing moisture in the air to condense.
Gravity-enhanced radiative cooling at KAUST
The KAUST research focused specifically on improving radiative cooling-based atmospheric water harvesting systems by increasing their passive efficiency.
“One common challenge in atmospheric water harvesting systems is that water droplets tend to remain attached to the surface, requiring active collection. Our coating effectively eliminated droplet adhesion, enabling truly passive water harvesting driven by gravity,” explained researcher Ahmad.
The solution builds on Gan’s previous “vertical dual-sided architecture,” originally designed to reflect thermal heat toward the sky to cool solar cells rather than to capture water.
The updated device retains this architecture but adds a lubricated elastomer layer infused with silicone oil on the condensation-facing surface. This modification allows water droplets to slide downward more easily under gravity, preventing accumulation and enhancing collection rates.
Performance results in Saudi field tests
The system was tested over one year in outdoor conditions in Thuwal, approximately 100 kilometers north of Jeddah.
Results showed promising performance. The passive water collection rate reached 21 grams per square meter per hour, roughly double that of a superhydrophobic surface. Under controlled indoor conditions (20°C and 80% relative humidity), the system achieved about 87% of the theoretical condensation limit, with 90% of total condensate collected passively.
The findings were published in Advanced Materials, highlighting the potential of gravity-enhanced atmospheric water harvesting systems for water-stressed regions.
