An atmospheric water generator (AWG) is a machine that pulls water from the air around us, creating clean drinking water. Water vapor in the air can be collected in several ways, such as cooling the air until it reaches a temperature where moisture can no longer stay in the air, using drying materials to absorb water vapor, employing special membranes that allow only water vapor to pass through, gathering water from fog, or increasing the air's pressure. AWGs are helpful in places where clean water is hard to find because water vapor is always present in the air. In busy cities, some systems use mesh technology built directly into building walls and rooftops to collect fog; these systems are known as building-integrated fog collectors.

AWGs may need a lot of energy to operate or can work without extra power by using natural temperature changes. Research inspired by nature discovered that the Onymacris unguicularis beetle can collect water from the air in a similar way.

A study found that AWGs could help supply clean drinking water to one billion people.

History

The Incas lived in high areas where rain does not reach by collecting dew and directing it to storage containers. Historical records show they used water-collecting fog fences. These methods did not require energy from outside sources and relied on natural temperature changes.

An emergency survival tool called the Armbrust cup was designed to collect water from breath condensation for use during emergency landings at sea.

In 2022, the US Army and US Navy signed a contract with Terralab and FEMA to use brine-based water extraction technology.

DARPA’s Atmospheric Water Extraction program seeks to create a device that can supply water for 150 soldiers and be carried by four people. In February 2021, General Electric received $14 million to continue developing their device.

In 2022, a desiccant made from cellulose and konjac gum was tested. It produced 13 liters per kilogram per day at 30% humidity and 6 liters per kilogram per day at 15% humidity. The desiccant releases water when heated to 60°C (140°F).

In 2024, researchers introduced a device using vertical copper fins spaced 2 mm apart. The fins are covered in copper foam coated with zeolite. Water is released when the copper sheets are heated to 184°C (363°F). The fins absorb moisture from air with 30% humidity once every hour. When heated hourly, the device produces 5.8 liters (1.5 gallons) of water per day per kilogram (2.2 pounds) of material.

Technologies

Cooling-based systems are the most common, while hygroscopic systems are becoming more promising. Hybrid systems use adsorption, refrigeration, and condensation together. Air wells are another method for passively collecting moisture.

Condensing systems are the most common method. They use a compressor to move refrigerant through a condenser and an evaporator coil to cool the air. When the air reaches its dew point, water condenses into a collector. A fan pushes filtered air over the coil. A purification system removes impurities and reduces risks from microorganisms.

The amount of water produced depends on the air's temperature, humidity, the air volume passing over the coil, and the machine's cooling power. Air water generators (AWGs) work best when the air is warm and humid. Generally, cooling condensation AWGs do not work well when the air temperature is below 65°F (18°C) or humidity is below 30%.

The Peltier effect in semiconducting materials provides an alternative condensation method. One side of the material heats, while the other cools. Air is passed over the cool side, lowering its temperature. Solid-state semiconductors are useful for portable devices but are less efficient and use more power.

Water production can improve in low humidity by using an evaporative cooler with brackish water to increase humidity. Greenhouses are special cases because the air inside is hotter and more humid. Examples include the seawater greenhouse in Oman and the IBTS Greenhouse.

Dehumidifying air conditioners produce non-potable water. The cold evaporator coil (below the dew point) condenses water vapor from the air.

When powered by coal electricity, this method has one of the worst carbon footprints of any water source (worse than reverse osmosis seawater desalination by 1,000 times) and uses more than four times as much water in its supply chain as it delivers to users.

Hygroscopic methods pull water from the air through absorption or adsorption, which dries the air. Desiccants can be liquid or solid. They must be regenerated (usually with heat) to recover the water.

The most efficient and sustainable method uses an adsorption refrigerator powered by solar thermal energy, which performs better than systems powered by solar electricity. These systems can use waste heat, such as for pumping or overnight operation, when humidity is higher.

In 2024, a new technology called sorbent-based atmospheric water harvesting (SAWH) used a fin-array adsorption bed powered by high-density waste heat. It produced 5.8 liters of water per kilogram of sorbent per day at 30% humidity using a 1-liter adsorbent bed and commercial materials.

Examples of liquid desiccants include lithium chloride, lithium bromide, calcium chloride, magnesium chloride, potassium formate, triethylene glycol, and [EMIM][OAc].

Concentrated brine can act as a desiccant. It absorbs water, which is then extracted and purified. Some systems produce 5 gallons of water per gallon of fuel. Brine streamed down tower sides absorbs water vapor. The brine enters a chamber under a partial vacuum and is heated, releasing water vapor that is condensed and collected. Gravity removes the condensed water, creating a vacuum that lowers the brine’s boiling point. The system can use passive solar energy.

Hydrogels can collect moisture, such as at night in deserts, to cool solar panels or create fresh water. One use is to irrigate crops by placing hydrogels near solar panel systems or under the panels.

Silica gel and zeolite remove moisture from pressurized air. One device uses 310 watt-hours (1,100 kJ) per liter of water. It uses a zirconium/organic metal-organic framework on a porous copper base attached to a graphite substrate. The sun heats the graphite, releasing water, which cools the graphite.

A hydrogen fuel cell car produces one liter of potable water for every 8 miles (12.87 kilometers) traveled by combining hydrogen with oxygen from the air.

Rooftop solar hydropanels can generate potable water using solar power and heat.

Energy

To get water from the air, energy is needed unless the air is very full of moisture. The amount of energy required depends on the humidity and temperature. This can be determined using a special calculation called Gibbs free energy.