The Earth’s atmosphere holds a vast reservoir of fresh water vapor. Capturing this moisture and converting it into liquid water, known as “getting water from air,” is gaining attention as a solution for sustainable water supply. This technology offers water access independent of traditional ground or surface sources, which are often strained.
Understanding Atmospheric Moisture
The presence of water in the air is governed by humidity and temperature. Humidity describes the amount of water vapor in the air. Relative humidity, commonly used, indicates how much water vapor the air holds compared to its maximum capacity at a specific temperature, expressed as a percentage. For example, air at 30°C (86°F) can hold about 30 grams of water vapor per cubic meter, while at 10°C (50°F), it holds approximately 9 grams.
Warmer air holds more water vapor than cooler air. When air cools to its dew point, excess moisture condenses into liquid droplets. Condensation, the transformation of water vapor into liquid water, is visible as dew, fog, or clouds. This natural phenomenon forms the basis for many water extraction technologies.
Key Water Extraction Methods
Extracting water from the air primarily relies on manipulating conditions that lead to condensation or absorption. Methods range from actively cooling air to using materials that naturally draw in moisture.
Condensation-Based Methods
Condensation-based methods cool air below its dew point, causing water vapor to condense. Active systems use refrigeration cycles, like air conditioners, to cool humid air over a surface. The collected water is then used.
Passive methods use natural temperature differences. Radiative cooling involves surfaces that cool by radiating heat to the night sky, often below the dew point. As moist air contacts these surfaces, water vapor condenses, forming collectible dew. This method is effective in regions with clear night skies and high atmospheric moisture.
Desiccant-Based Methods
Desiccant methods use materials with a natural affinity for water. These hygroscopic desiccants absorb moisture from the air via adsorption. Common desiccants include silica gel, activated alumina, and molecular sieves. Once saturated, the desiccant is heated to release absorbed moisture as vapor, which is then cooled and condensed into liquid water.
Desiccant systems are effective even in drier environments, as they do not depend on reaching a specific dew point. However, desiccant regeneration often requires significant energy. Desiccant choice depends on factors like moisture removal capacity and operating temperature.
Fog Harvesting
Fog harvesting captures water from fog droplets. It involves setting up large mesh nets in areas prone to frequent fog. As wind pushes fog through the mesh, droplets adhere to the netting. Gravity causes these droplets to combine and trickle into collection troughs.
This method is effective in coastal or mountainous regions with consistent fog, such as Chile, Peru, and Ecuador. It requires no external energy, making it a low-cost, sustainable option for suitable communities. The efficiency of fog collectors can vary, with some yielding 3 to 10 liters of water per square meter per day.
Real-World Water Generation
Water extraction methods have led to practical applications, from industrial systems to personal devices. These technologies provide solutions for water scarcity. Deployment depends on local climate, energy availability, and water demand.
Atmospheric Water Generators (AWGs)
Atmospheric Water Generators (AWGs) use condensation-based methods and refrigeration cycles to produce potable water. They draw in ambient air, filter it, and cool it below its dew point to condense water vapor. The collected water is then filtered and purified for drinking.
AWGs range from compact residential units producing a few liters daily to large industrial systems generating thousands of liters. Residential units might produce 2-10 gallons (7.5 to 38 liters) per day under optimal conditions, while industrial models can exceed 20,000 liters per day. Effectiveness depends on ambient temperature and humidity, with optimal performance above 18°C (65°F) and 60% relative humidity.
DIY Approaches
Individuals can employ simple, low-cost methods for collecting atmospheric moisture. One approach involves collecting condensation from cold surfaces, such as a chilled metal sheet or a tarp stretched over a cool night surface. As the surface cools, dew forms and can be collected. These methods are low-yield but can provide small amounts of water in survival or emergency situations.
Solar stills, primarily for purifying contaminated water or desalinating saltwater, can also collect atmospheric moisture. They use solar energy to create a temperature differential, causing water to evaporate and condense on a cooler surface. Though not specifically designed for atmospheric moisture, some designs capture dew or vapor from the air within an enclosed system.
Global Impact and Use Cases
Atmospheric water generation technologies address water needs in various scenarios. In remote areas, AWGs offer an independent source of clean drinking water, avoiding extensive piping or drilling. They are valuable in disaster relief, providing immediate access to safe water when conventional supplies are disrupted.
Military operations use portable AWGs to reduce reliance on water transport, enhancing field self-sufficiency. For homes and businesses, these systems supplement existing water sources, providing water security, especially in drought-prone regions. Continued development of energy-efficient, cost-effective solutions expands the potential for atmospheric water harvesting globally.