Fog nets are large mesh panels, typically stretched between posts on hillsides or ridgelines, that intercept wind-driven fog and turn it into drinkable water. As fog passes through the mesh, tiny water droplets stick to the fibers, merge into larger drops, and drain by gravity into a gutter and collection tank below. In the right climate, a single square meter of mesh can harvest several liters of water per day, making fog nets one of the simplest and lowest-cost technologies for producing fresh water in arid regions where rain is scarce but fog is frequent.
How Fog Becomes Water on a Net
Fog is essentially a ground-level cloud: a mass of air carrying millions of suspended water droplets, most of them smaller than about 40 micrometers across. When wind pushes this cloud through the mesh of a fog net, some of those droplets collide with the fibers instead of passing through the gaps. The droplets that stick to a fiber grow as more droplets land on them. Once they get heavy enough, gravity pulls them downward along the fiber, merging with other droplets on the way. Researchers have documented several transport mechanisms during this drainage: gravitational draining, droplet bouncing, and a sweeping effect where a sliding drop picks up smaller ones in its path.1Experiments in Fluids. Experimental analysis of droplet coalescence and transport mechanisms on a single vertical fiber Eventually the water reaches a gutter at the bottom of the mesh, which channels it into a pipe running downhill to a storage tank.
Collection efficiency depends heavily on both fog characteristics and wind speed. The fraction of available fog water that a mesh actually captures tends to decrease as the fog’s droplets get larger (above roughly 10 micrometers in mean diameter), because bigger droplets have more momentum and may bounce off or be deflected around the mesh. At the same time, stronger winds push more fog through the mesh per unit of time and improve capture of the larger droplets, so windier conditions generally yield more water when the fog is composed of medium-to-large droplets.2Atmospheric Research. Collection efficiency of fog events
The Standard Mesh and Why Its Design Matters
The most widely used fog-collection mesh is a black polyethylene Raschel netting, originally manufactured in Chile for agricultural shade cloth. It is UV-treated, lightweight, cheap, and easy to transport to remote sites. Its knitting pattern creates continuous filaments running in one direction but discontinuous ones in the other, which gives the material noticeably different stretch and strength depending on which way you pull it.2Atmospheric Research. Collection efficiency of fog events That asymmetry matters for structural engineering: a large panel has to absorb wind loads without tearing or sagging into a shape that spills water off the sides rather than funneling it into the gutter.
One of the most important design parameters is the shade coefficient, which is simply the fraction of the mesh’s area that is blocked by fibers rather than open to airflow. Set the shade coefficient too low and most fog passes through uncollected. Set it too high and the mesh acts like a wall, forcing the wind (and the fog it carries) to flow around the net instead of through it. Research has converged on a sweet spot: an optimum shade coefficient of roughly 50 to 60 percent for fog collection.3Water Resources Management. Evaluating Mesh Geometry and Shade Coefficient for Fog Harvesting Collectors Fiber diameter also plays a role. Thinner fibers catch smaller droplets more efficiently, because the airstream around a thin fiber is less disturbed and droplets are more likely to collide with it rather than be carried past.
Some researchers have moved beyond flat Raschel mesh entirely. Three-dimensional spacer fabrics, which look like two mesh layers connected by angled fibers, showed the highest collection efficiencies in controlled comparisons, likely because the internal spacer fibers create extra interception surfaces and slow the droplets down.4Journal of Industrial Textiles. Evaluation of the geometrical parameters of collector mesh on the fog collection efficiency Another promising approach uses a “harp” structure of parallel vertical yarns with extremely fine hair fibers sprouting from them. These hairy yarns increase the shade coefficient without substantially increasing the pressure drop across the collector, and their parallel arrangement forms channels that move water down by capillary action, reducing the clogging that happens when large drops block the mesh openings. In lab tests, this design captured roughly two and a half times more water than optimized Raschel mesh.5PubMed Central. Fog collection improvement using harp structures formed from hairy yarns
The Shape of the Collector Itself
Most deployed fog nets are flat rectangular panels, but flat is not necessarily best from an aerodynamic standpoint. Computational fluid dynamics simulations have shown that V-shaped collectors, where two mesh panels meet at a low opening angle, outperform flat panels in aerodynamic efficiency. The V-shape effectively increases the capture area presented to the wind while reducing the pressure drop through the mesh, meaning more fog passes through rather than deflecting around it.6International Journal of Heat and Fluid Flow. A CFD study of the aerodynamic efficiency of V-shaped fog water collectors The trade-off is that non-flat designs are harder to build and maintain on remote hilltops, which is why simple flat panels remain the default in most community projects.
Where Fog Nets Work Best
Fog collection is not viable everywhere. The technology depends on consistent, wind-driven advection fog, the kind that forms over cold ocean currents and is pushed inland and upward by prevailing winds. Coastal mountains in arid and semi-arid regions are the prime candidates, because they offer both abundant fog and severe water scarcity. The technology has been deployed or tested in at least a dozen countries, including Chile, Peru, Morocco, Namibia, South Africa, Eritrea, Ethiopia, Guatemala, Colombia, Israel, Oman, and the Canary Islands.7Frontiers in Water. Research History and Functional Systems of Fog Water Harvesting
Yield varies dramatically with local conditions. A model applied to three sites along the Chilean coastal mountains found that hyperarid sites in the north could reach about 10 liters per square meter per day, while arid sites further south peaked at around 5 liters and semi-arid sites at about 3 liters per square meter per day. All three sites experienced fog more than 40 percent of the time.8Hydrology and Earth System Sciences. Observation-driven model for calculating water-harvesting potential from advective fog in (semi-)arid coastal regions In Morocco’s Sidi Ifni project, one of the longest-running operational systems, annual average harvest rates ranged from about 1.6 to 6 liters per square meter per day depending on the season and year.9Journal of Arid Environments. Multi-aspect assessment of operational fog collection systems: A rural development perspective, insights from the Sidi Ifni project in Morocco Those numbers may sound modest, but a large fog collector with 40 square meters of mesh area at the Chilean hyperarid site could produce hundreds of liters on a good fog day.
Wind, the Friend and Enemy
Wind is essential to fog collection, because without it, fog sits still and few droplets reach the mesh. But strong gusts are also the main cause of structural failure. Wind pressure can deform the mesh, concentrate stress at the points where it is attached to the frame or cables, and eventually rip the mesh or collapse the entire structure. Field analyses in Chile and elsewhere have found that the weakest point is usually the mesh near its attachment points, where stress concentrations build up as the panel billows under wind load.10Atmospheric Research. Large fog collectors: New strategies for collection efficiency and structural response to wind pressure
Designers have responded with reinforced attachment systems, tensioned cable supports, and mesh panels that can be lowered during storms. Some projects use multiple smaller panels rather than one large one, reducing the total wind load on any single structure. Getting this right is critical for long-term viability: a fog net that tears every few months is not a sustainable water source, no matter how much water it collects between failures.
Is the Water Safe to Drink?
Fog water is generally clean enough to meet basic drinking water guidelines, with most studies reporting that major mineral concentrations fall within World Health Organization standards. But fog acts as an atmospheric scrubber, picking up whatever is floating in the air. In coastal areas, dissolved sulfates from oceanic emissions can make fog slightly acidic. Near industrial zones, the problem gets worse. An acidic pH is not dangerous on its own, but it can leach heavy metals from aerosol particles trapped in the fog. At a collection site in northern Chile, for example, researchers found selenium, arsenic, and nitrate levels exceeding Chilean potable water guidelines. Elevated aluminum, iron, and lead have been detected in fog and dew water collected in France.11PubMed Central. Fog and Dew as Potable Water Resources: Maximizing Harvesting Potential and Water Quality Concerns
The practical implication is that fog water quality depends almost entirely on local air quality. A remote mountaintop upwind of clean ocean air will yield water that is essentially ready to drink with minimal treatment. A site downwind of mining operations or heavy industry may produce water that needs filtration or chemical treatment. Routine testing is important, and few community-scale projects have the resources to do it rigorously. Biological contamination is generally less of a concern than chemical contamination, because the water is collected without contact with soil or surface sources, but storage tanks still need to be covered and periodically cleaned.
Real-World Community Projects
The longest and most closely studied fog collection programs are in Chile and Morocco. Chile’s Atacama Desert coast, where fog blankets the mountains while rain almost never falls, has been a testing ground for fog nets since the 1980s. Morocco’s Dar Si Hmad project in the Aït Baamrane region near Sidi Ifni, which became operational in 2015, is frequently cited as a model for community-driven fog harvesting. The project trained local community members, with a particular focus on women, to operate and manage the fog-water system.12Procedia Engineering. Harvesting Fresh Water from Fog in Rural Morocco: Research and Impact Dar Si Hmad’s Fogwater Project in Aït Baamrane Assessments show the project continues to deliver improved drinking water access, and interviews confirm strong social commitment from the local community.9Journal of Arid Environments. Multi-aspect assessment of operational fog collection systems: A rural development perspective, insights from the Sidi Ifni project in Morocco
Community engagement turns out to be one of the strongest predictors of whether a fog collection system lasts. Reviews of projects across multiple countries have identified local participation, women’s empowerment, capacity training, and involvement of local institutions as the key drivers of sustainability.7Frontiers in Water. Research History and Functional Systems of Fog Water Harvesting Projects installed by outside organizations without deep local buy-in have a history of falling into disrepair once the initial funding period ends. The technology is simple enough that local people can maintain it, but only if they are trained and invested from the start.
How Nature Harvests Fog
Fog nets are, in a sense, artificial versions of something that trees and other organisms have been doing for millions of years. In California’s redwood forests, the dominant canopy species, coast redwood, absorbs fog water directly through its leaf surfaces. During heavy fog, the direction of water flow in the tree’s xylem actually reverses, pulling water inward from the foliage rather than upward from the roots, with instantaneous inward flow rates peaking at about 5 to 7 percent of maximum transpiration rate.13Plant, Cell & Environment. The contribution of fog to the water relations of Sequoia sempervirens (D. Don): foliar uptake and prevention of dehydration This is not unique to redwoods: roughly 80 percent of the dominant plant species in the redwood forest community use foliar water uptake as a water acquisition strategy.14PubMed Central. Foliar water uptake: a common water acquisition strategy for plants of the redwood forest
The Namib Desert beetle, which lives in one of the driest places on Earth, has inspired a separate line of research. Its back features a pattern of hydrophilic (water-attracting) bumps surrounded by hydrophobic (water-repelling) troughs. Fog droplets condense preferentially on the bumps, grow, and then roll off the waxy troughs into the beetle’s mouth. Researchers have mimicked this by 3D-printing bumpy surfaces combining superhydrophilic and hydrophobic polymers. In laboratory tests, the best beetle-inspired surface achieved a fog collection rate of about 365 grams per square meter per hour, substantially outperforming flat surfaces made of either material alone.15PubMed Central. Desert Beetle-Inspired Hybrid Wettability Surfaces for Fog Collection Fabricated by 3D Printing and Atmospheric Pressure Plasma Treatment
Janus Meshes and Other Advanced Surfaces
One of the persistent problems with traditional fog nets is clogging: once enough water accumulates on the mesh, droplets bridge the openings, block airflow, and collection efficiency drops until the water drains or blows off. A growing body of research addresses this through “Janus” meshes, named for the two-faced Roman god because they have different surface properties on the front and back. The fog-facing side is made hydrophobic to prevent water from spreading into a film, while the back side is hydrophilic to wick water away quickly. This wettability gradient drives captured water from the front surface through to the back, where it drains rapidly, keeping the front clear for continued collection.16PubMed Central. Unclogged Janus Mesh for Fog Harvesting
Recent Janus membrane designs have pushed this concept further. One approach uses a membrane with high-contrast wettability that can transport even tiny droplets (less than 0.1 microliters) directionally, achieving collection efficiencies of over 15 grams per hour per square centimeter, far higher than conventional Janus membranes.17Journal of Materials Science & Technology. A new Janus mesh membrane with ultrafast directional water transportation and improved fog collection Another team developed a three-dimensional origami structure shaped like a trumpet flower, with Janus surface properties that allow it to harvest fog from any direction. By combining the wettability gradient with superhydrophilic channels cut into the surface, the design keeps both sides effectively dry at all times, preventing the clogging that plagues flat collectors.18PubMed. An Efficient Fog Collection Origami Janus Membrane for Rapid Directional Water Transport and Omnidirectional Fog Harvesting
These are still laboratory-scale achievements, not field-deployed systems. Scaling a Janus membrane from a lab bench to a hilltop in Morocco is a very different engineering challenge. But the performance gains are large enough that bridging that gap is an active area of research.
Combining Fog Collection with Solar Desalination
Fog tends to be heaviest at night and in the early morning, while solar energy is available during the day. This complementary timing has inspired hybrid systems that harvest fog after dark and use sunlight to purify or desalinate water during the day. One design uses hierarchically porous microneedle arrays that function as efficient fog catchers in humid nighttime conditions and as photothermal evaporators under daytime sun, driving solar desalination. By combining both water-harvesting routes across a full daily cycle, the system could theoretically deliver an overall water yield approaching 200 kilograms per square meter, a dramatic increase over either method used alone.19Advanced Functional Materials. High‐Performance Freshwater Harvesting System by Coupling Solar Desalination and Fog Collection with Hierarchical Porous Microneedle Arrays
Hybrid systems like this remain experimental, but they point toward a future where fog collection is not a standalone curiosity but part of an integrated, low-cost water production toolkit. For coastal communities in arid zones where fog, sun, and seawater are all abundant, the combination could eventually provide reliable fresh water without any external energy input or infrastructure.
What Fog Nets Cannot Do
For all their appeal, fog nets have real limitations that proponents sometimes gloss over. They only work where there is regular, wind-driven fog. Inland deserts that are dry as well as hot get no benefit. Even in ideal locations, fog is seasonal: many sites have a distinct fog season lasting a few months, and collectors produce little or nothing outside it. That means fog water almost always needs to be supplemented by another source during dry months, or stored in large enough tanks to last the gap.
Yields are also modest compared to conventional water infrastructure. A large fog collector might produce a few hundred liters per day, enough for a small village’s drinking water needs but nowhere near enough for irrigation or industry. Fog collection is best understood as a supplemental drinking water source for remote communities that currently rely on trucked water or long walks to distant wells. Describing it as a solution to regional water scarcity would be an overstatement.
Maintenance is another underappreciated challenge. UV radiation degrades polyethylene mesh over a few years. Wind tears panels. Dust and biological growth can coat fibers and reduce their ability to capture droplets. The concrete and metal support structures need periodic inspection. None of this is technically difficult, but it requires ongoing effort and a small budget, which is why community ownership and training matter so much.
Fog Collection and Reforestation
Beyond providing drinking water, fog nets have been used to support tree planting in arid regions. The logic is straightforward: young trees in fog zones often die not because the climate is permanently hostile, but because they cannot survive the first few dry seasons before their roots reach deep enough to access groundwater or intercept fog drip on their own. Fog-collected water can irrigate seedlings during this vulnerable establishment period. Once the trees mature, their canopies become natural fog collectors, dripping intercepted moisture onto the soil and reducing evaporation beneath them. Fog water has been recognized as a resource for afforestation, gardening, and drinking water for both human and animal consumption.20PubMed Central. Fog as a fresh-water resource: overview and perspectives
This creates an interesting positive feedback loop in some ecosystems: fog nets enable reforestation, reforestation increases natural fog interception, and the restored forest eventually reduces the community’s dependence on artificial fog collectors. Whether this works in practice depends on the specific ecology, but it has been attempted in several locations in South America and Africa, with enough anecdotal success to keep drawing interest from restoration ecologists.