Stealing Water from the Sky: Fog Catching
Growing up near San Francisco, California (and now living there) I have always had to deal with the inevitable fog that rolls in from the ocean seemingly every day. Everyone is always complaining about the fog ruining their day and the depression of weeks on weeks of endless fog. Needless to say, I have never been very fond of the stuff. Because the people living in the San Francisco area are very fortunate and don’t have to worry about water thanks to the melting snow pack that provides us clean water that lasts all year, fog was always just a nuisance. However, there are many places in the world where water is scarce and fog can instead be a blessing.
Scientists have found that as long as 2,000 years ago people were taking advantage of the fog as a source of water. They used a very simple technique that is not very different from modern rainwater harvesting. People noticed that when fog passed through an area some of the moisture was caught in the trees and other vegetation. So one day someone decided to put a pot under a tree and catch the water as it ran off of the leaves, much like water is collected as it runs off a roof nowadays, and after some time they had a pot with clean water in it, and from that day forward I’m sure that person was very popular.
Today this same technique can be used, however, there are other ways to capture the water using what are now called “fog catchers”. Using a fog catcher is different than collecting water that condenses on leaves. For the most part fog catchers are made from netting or mesh that is suspended between two poles and is set up in the path of the fog, often along a hill or ridge. When the fog hits the netting or mesh it actually sticks to it, and as more fog sticks drops form, and then the drops can be collected. There are different ways to collect the water, but the basic idea is that gravity will pull the drops down to the bottom of the net or mesh and then fall off. A gutter of some type catches the drops and channels them into a holding tank. Very simple and very basic but life changing.
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Fog catchers can be made out of many different materials which makes fog catching an appropriate practice that can be used all over the world. On the outskirts of Lima, Peru lies the neighborhood of Flor de Amancay, a small rural settlement that gets fog nine months out of the year. Here they strung up plastic mesh between eucalyptus posts in order to make four billboard sized fog catchers (6m x 4m). In past years between April and December they have been able to collect up to 600 gallons (2,271 liters) a day! Because they are so successful there are 26 other fog catchers installed throughout Lima, and more are on their way.
In the Atacama Desert in Chile, the driest desert on Earth, they are using polyethylene or polypropylene mesh to capture the fog that rolls in along the coast. They have several fog catchers set up, each 48 meters, which are able to collect 264 gallons (1,000 liters) per day.
In Napal, up to 132 gallons (500 liters) per day have been collected to serve the Prathivara Temple. There are currently several other projects going on throughout Nepal to collect water using fog catchers.
In Venda, South Africa fog catchers have captured an average of 80 gallons (300 liters) a day, however, they have been able to capture up to 1,000 gallons (3,800 liters) in a single foggy day! These numbers are all very impressive and are a testament to what these fog catchers can provide.
At the forefront of the fog catching movement is an organization named FogQuest. FogQuest has been around since 2000 and has completed or is currently working on projects in Yemen, Namibia, Haiti, Ethiopia, Guatemala and Morocco to name a few. If you’re interested in catching some fog they can be a great resource. Alimon is another organization working on fog harvesting.
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A couple of things I wanted to mention. One is that if you think your climate is appropriate for this type of water harvesting there is mesh that is specifically designed for this purpose that you can buy, however, it’s my opinion that while it may not be as efficient, any sort of mesh should be able to get the job done. Saying that, you MUST make sure that everything is clean before it is put into use in order to avoid contaminating the water you collect. Also, this type of system is probably not going to be enough for a large number of people, however, it can be very effective for small communities. Further, because fog catching relies on the weather it isn’t completely reliable, and therefore, if possible, you might want to have a backup plan. Finally, before spending a lot of time or money on fog catching you should make a trial run and make sure your climate is appropriate for this type of harvesting.
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I originally came upon the idea of fog catchers when I was looking for a way to harvest water at my house in San Francisco to use for irrigation. My house has a flat roof which means that I can’t harvest rainwater with traditional methods, however, I was thrilled to find this method and am looking forward to trying it out. In suitable climates fog catching can be a simple and appropriate way to harvest clean water for either irrigation or drinking water, and with proper maintenance and storage capacity can provide water throughout the year. It’s always exciting for me to find technologies like this to pass along to my readers, and hopefully this can help bring clean water to those in need. Thanks for reading, and if you’ve had any experience with fog catching please leave a comment below and let me know how your experience went. Below you’ll find a video talking about fog catching in the Atacama Desert in Chile.