Fog water collection systems provide an opportunity to build water resilience by harnessing an environmental feature endemic to areas along the Central Coast of California (fog). Around the world, people living in areas with little rainfall use fog to capture potable water. In some cases, entire communities use fog to meet their basic needs. A fog collector system is comprised of a square of vertically mounted mesh, typically made of nylon, polyethylene, or polypropylene, that can capture several gallons of water in a single day under the right conditions. In this way, fog water collection meshes are an example of biomimicry in the sense that their fibers combine and channel water like the way the surface and ridges of a leaf collect dew along its stem.
Humans have been collecting fog for many years. There is evidence that communities in Chile were harvesting fog 12,000 years ago. Today, people in Chile still collect fog water in areas with intense fog and little precipitation. In South America’s Atacama Desert and in Egypt, piles of stones were arranged so that condensation could trickle down the inside walls where it was collected and then stored.
What is fog?
Fog forms when the difference between the dry bulb temperature and the condensation temperature (dew point) is less than 4°F. In these conditions, the relative humidity of the air reaches nearly 100%, and the air cannot hold any additional moisture. However, there are cases where fog can form at lower relative humidity, and there are instances where fog does not develop when the relative humidity reaches 100%.
Fog formation involves the elements required for cloud formation (e.g., condensation nuclei in the form of dust, aerosols, pollutants, etc.). When there are exceptional amounts of condensation present, especially hygroscopic (water seeking) particles such as salt, water vapor can condense when the relative humidity is less than 100%. Sea fog is a type of fog that forms under such conditions. As the name suggests, sea fog is common along coastlines where airborne salt particles are generated by crashing waves. Due to the hygroscopic nature of salt, condensation can occur when the relative humidity is as low as 70%.
Factors to consider when identifying a suitable fog water harvesting site
The feasibility of artificial fog catchers depends on the meteorology and topography of the area. Moist air must be driven by the wind to a geographic barrier, such as a mountain, that intercepts the clouds. The following factors affect the volume of water that can be extracted from fog and the frequency at which that water can be harvested.
- The frequency of fog is a function of atmospheric pressure, oceanic water temperature, and the presence of thermal inversions.
- Altitude, seasons, and terrain features can affect the fog water content.
- Wind velocity and direction greatly impact the volume of fog water that can be collected.
- Distance from the coast will affect how much fog can be generated. There are many high-elevation continental locations with frequent cover resulting from either the transport of upwind clouds or the formation of orographic clouds. In such cases, the distance to the coastline is irrelevant. However, areas of high relief near the coastline are generally preferred sites for fog harvesting.
- The orientation of the topographic features also impacts the amount of fog water harvesting. Clouds will flow over the ridge lines through passes, with the fog often dissipating on the downwind side.
- As previously mentioned, the wind is an important aspect of fog water collection. Studies have shown that the optimal wind speed for collecting fog water is between 8 mph and 20 mph (Schemenauer and Cereceda, 1994; Schemenauer and Joe (1989); Bridgman et al. (1994); and Marzol (2008).
Fog Water Harvesting in California
If you search for fog water harvesting studies online, you will find that a significant amount of research has been conducted by Dr. Daniel Fernandez, a professor, and researcher at California State University Monterey Bay. He also founded Bayside Fog Collectors, which is based out of Marina, California. The mission of Bayside Fog Collectors is to supply customers with high-quality fog collectors for research and hobby purposes. Dr. Fernandez gave a Ted Talk in 2011, which is shown below.
For example, a study conducted by researchers at the Fernandez Lab at California State University, Monterey Bay, measured the amount of fog collected from mesh-screen fog collectors installed at the Brazil Ranch near Big Sur, California during the summer seasons of 2010 and 2011. The study found that fog deposition occurred during 73% of the recorded days in 2010 and 87% of the recorded days in 2011. The daily average deposition rate was 0.5 gal/yd2 in 2010, and 0.9 gal/yd2 in 2011 (Hiatt et al., 2012). These results show that fog water harvesting could be used in areas where drought is becoming more severe, such as the Central Coast of California. However, it is worth noting that the amount of water collected by a fog water harvesting system is very location-dependent. The amount of fog collected is a function of the density of water in the air, wind speed, and wind direction. More fog will be collected on a mesh when the wind is blowing directly on it.
Collected fog water can be used for irrigation or potable water. Hangar 1, a distillery in the San Francisco Bay area, even makes vodka out of fog water. It should be noted that fog has been found to convey mercury from ocean upwelling. However, researchers have stated that the levels of mercury found in fog (to date) are not dangerous to humans.
How to Build Your Own Fog Water Harvesting Collector
Fog water collection systems are fairly simple to build. Bayside Fog Collectors provides step-by-step instructions free of charge online. In summary, a standard fog collector (SFC) has a fog-collecting area of 1 m2 (10.8 ft2). The mesh sits on a base that is 6.5 feet above the ground with the top of the mesh 9.8 feet above the ground. You can also purchase the materials online at Bayside Fog Collectors.
FogQuest, which is a non-profit, registered Canadian charity dedicated to planning and implementing water projects for rural communities in developing countries, is another good source of information for those who are seeking to build their own fog water harvesting systems. FogQuest has a fog water collection manual available for $24.99 on their website.