Fog collection, also called fog harvesting, is a method of gathering water from fog. It uses large vertical mesh nets to help fog droplets move downward into a trough below. This setup is called a fog fence, fog collector, or fog net. When air cools, water vapor in the air condenses into droplets of liquid water, known as dew. This process is most visible on thin, flat surfaces like plant leaves and grass blades. As these surfaces cool by releasing heat into the sky, water vapor condenses faster than it can evaporate, forming droplets.
Water vapor condenses on the parallel wires of the mesh net and collects at the bottom. This process requires no outside energy and relies on natural temperature changes, making it useful in areas with limited resources. The term "fog fence" describes its long, rectangular shape, but fog collectors can have different designs. The effectiveness of a fog collector depends on the net material, the size of the holes, the thickness of the wires, and any chemical coatings. Fog collectors can collect 2% to 10% of the moisture in the air, depending on their design. Ideal locations are high-altitude dry areas near cold ocean currents, where fog is common, allowing fog collectors to produce the most water.
Historical origin
The systematic gathering of dew or condensation using natural or human-made methods is an old practice. People have collected condensation from plant stems for drinking, a method still used today by survivalists. In dry areas like the Atacama and Namib deserts, fog is used to provide water for plants without rain. The earliest known human-made fog collectors date back to the Inca Empire, where buckets were placed under trees to collect condensation.
Other early examples of human-made dew collection include ancient stone piles in Ukraine, medieval dew ponds in southern England, and volcanic stone covers on farmland in Lanzarote. These structures may have been used to trap dew.
One of the first recorded fog collection projects happened in 1969 in South Africa to supply water to an air force base. The setup included two fences 100 meters long (about 1,000 square feet). Over 14 months, the system collected about 11 liters (2.5 gallons) of water daily, or about 110 milliliters (⅓ fluid ounce) per square meter. A larger study in 1987, led by the National Catholic University of Chile and the International Development Research Centre in Canada, built 100 fog fences in northern Italy, each 48 meters long (about 520 square feet). This project collected about 0.5 liters (1.5 fluid ounces) of water per square meter daily, providing 33 liters (8 gallons) of water each day for 300 villagers.
In nature
In nature, some insects and plants use a method called fog collecting to gather water. Namib Desert beetles obtain water through condensation that forms on their wings. Their wings have a special pattern of areas that attract water and areas that repel water. Redwood forests rely on water collected from condensation on tree needles. This water drips into the roots of the trees, helping them grow even in areas with little rainfall.
Parts of a fog collector
The fog collector has three main parts: the frame, the mesh netting, and the trough or basin.
The frame holds up the mesh netting and can be made from many materials, such as stainless steel poles or bamboo. The frame can have different shapes, including linear (like a fence) or cylindrical. Linear frames are rectangular with vertical ends buried in the ground. They use ropes tied to the top and staked into the ground to stay stable.
The mesh netting is where water droplets form. It is made of thin threads woven together with small holes. A chemical coating helps increase condensation. Shade cloth is often used for the mesh because it is easy to find in areas with limited resources. The threads are treated to both attract and repel water, which helps collect more moisture. This design can capture 2% of the moisture in the air. When the threads and holes are smaller, the efficiency improves. The best mesh uses stainless steel threads about the size of three to four human hairs, with holes twice as large as the threads. The coating reduces how strongly water droplets stick to the surface, allowing more small droplets to form. This type of netting can capture 10% of the moisture in the air.
Under the mesh netting, a small trough collects the water. The water flows from the trough into a storage container or irrigation system for use. If the fog collector is circular, the water is collected in a basin placed at the bottom of the netting.
Principle
Fog usually has between 0.05 to 1 gram of water in each cubic meter (⅗ to 12 grains per cubic yard). The water droplets in fog are between 1 to 40 micrometers in size. Fog moves slowly and is carried by the wind. For this reason, a good fog fence must be placed to face the main direction of the wind and must have a fine mesh. Wind would flow around a solid wall and take the fog with it.
Water droplets in the fog land on the mesh. When a second mesh rubs against the first, the droplets join together and flow down to the bottom of the mesh. The water can then be collected and taken away.
Advantages and disadvantages
Water can be collected in any environment, even very dry places like the Atacama Desert, which is one of the driest areas on Earth. Water collected from fog can sometimes be safer to drink than water from the ground. Fog collection systems are easy to maintain because they do not need electricity and only require occasional cleaning of the nets to keep them free of dirt. In some areas, parts of the system can be found locally, making it easier to repair the system if it breaks and preventing it from being unused. No special training is needed to fix the system. Fog collectors are cheaper to set up compared to other water collection methods.
Fog collectors can only collect a certain amount of water based on the local weather and the way the land is shaped. They cannot produce more water when needed, and the amount of water they collect changes throughout the year due to local weather and large weather patterns like El Niño. The water collected may become dirty from dust, birds, or insects. The moisture collected can also cause mold and other harmful microorganisms to grow on the mesh.
Modern methods
In the mid-1980s, the Meteorological Service of Canada (MSC) started building and placing large fog collection devices on Mont Sutton in Quebec. These tools were made of a large canvas (about 12 meters long and 4 meters high) stretched between two wooden poles, held up by wires. A long trough was placed underneath. Water from the fog would collect on the canvas, join into drops, and then slide down to fall into the trough below.
In busy city areas, the same mesh technology can be built directly into building walls, roof parts, or sun-shading structures. These systems are called building-integrated fog collectors (BIFCs).
The goal of the Canadian project was to study the makeup of fog using these devices. However, their success interested scientists in Chile’s National Forest Corporation (CONAF) and the Catholic University of Chile. These groups wanted to use fog collection to collect camanchaca or garúa clouds that cover northern Chile during winter. With help from the International Development Research Centre (IDRC), the MSC worked with Chileans to test different designs on El Tofo Mountain in northern Chile. In the Atacama Desert near Huasco, farms had water shortages because rivers were drying up. Two-hundred-meter fog-catching water towers were built, producing 10,000 to 50,000 liters of water daily. This water now supports farming communities without using river water. The project near Huasco won the Next Generation First Prize in Latin America for helping the environment.
After the system was improved, about 50 of these systems were built to water seedlings on a hillside to help plants grow again. Once plants grew, they were expected to collect fog themselves, like cloud forests in South America, to create a self-sustaining system. The success of the reforestation project is unknown. However, about five years after the project started, the nearby village of Chungungo asked for a pipeline to bring water down the mountain. Though CONAF was not involved in this request, the collection system was expanded to include 94 nylon mesh collectors, a storage tank, and pipes to provide water to 300 people in Chungungo.
In 2002, the IDRC reported that only nine of the devices remained, and the system was in poor condition. However, the MSC stated in its article that the facility was still working in 2003, though it did not explain why. In June 2003, the IDRC said plans existed to restart the site on El Tofo.
In early 2025, researchers in Chile found that capturing water from fog on a large scale could help some of the driest cities in the world get drinking water. In Alto Hospicio, a city in the Atacama Desert, researchers collected fog. This area gets less than 0.19 inches (4.8 mm) of rain each year and faces challenges like poverty and reliance on water delivered by trucks.
In March 2015, a Moroccan organization called Dar Si Hmad (DSH) built a large fog collection and water distribution system in the Anti-Atlas Mountains. This area has little water but has fog for six months of the year. DSH’s system used technology that sent messages via SMS to monitor the water system. This helped manage how fog collection affected local communities. MIT researchers said DSH’s methods improved fog collection efficiency by about 500%.
Even though the project in Chungungo had problems, fog collection has been used in other places worldwide. The International Organization for Dew Utilization is developing foil-based condensers for areas where rain or fog cannot provide enough water all year. After the initial success, researchers formed a nonprofit called FogQuest. FogQuest has set up working systems in Yemen and central Chile, and others are being tested in Guatemala, Haiti, and Nepal. These projects now focus more on involving local communities to ensure long-term success. Fog collection systems are now used in villages across 25 countries. These systems could help grow plants in dry areas. Simple fog collectors are expected to continue being used. Some attempts to build fog catchers in Peru have had mixed results.