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.

 

 

Sources:

Fog – National Geographic Encyclopedic Entry

Fog Catchers Bring Water to Parched Villages

Aleszu Bajak: Catching Fog in Lima

Giant “Fog Catchers” Provide Water in the Desert

Nepal – Fog Collection Operational Project

Water Harvested from Clouds in Rural South Africa

FogQuest Website

 

Stealing Water from the Sky: Fog Catching

10 thoughts on “Stealing Water from the Sky: Fog Catching

  • May 8, 2013 at 12:20 pm
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    I have casually followed the concept of fog harvesting for several years, and have always felt they are mostly confined to the western coastal areas were trade winds come off the open sea with sufficient reliability for nearly daily fog.

    I also got the impression that those in Chile and Peru had been abandoned or at least were for a while. And thus I wonder how durable the mesh is and how often it might have to be replaced particularly if there are any strong winds coming through the areas. I can see a fairly frequent need to replace the mesh at considerable cost.

    Also, for irrigation purposes you might want a quick estimate of water requirements as 1 lit/sec/ha. continuous flow. That is a lot of water.

    Thank you.

    Reply
  • February 2, 2015 at 1:12 pm
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    I just found this entry. Did you ever try and implement a fog catcher at your house? If so, is there an entry explaining how it worked/how you built it?

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    • February 16, 2015 at 4:29 pm
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      Hi Sean,
      I have not. I’ve been planning on building one, but as things go…I haven’t gotten around to it yet. Once I do I will be sure to post something about it.

      Thanks,
      Brian

      Reply
  • February 17, 2015 at 11:37 am
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    I very much like the idea of fog catchers but was concerned a few years ago when I saw an article out of Chile indicating that many of the fog catchers had fallen in disrepair.

    While the number seem impressive may I interpret the 2,271 liter/day. If the potential ET rate is 6 mm/per day than 0.6 liters will be able to irrigate 1square meter or the 2,271 liter will irrigate 3785 sq meters or 0.37 ha. Also, it you accept the World Health Organizations claim that minimum water per person is 50l liters/day than the 2,271 liter will provide enough water for 45 people.

    Is that really enough?

    Reply
  • June 16, 2015 at 8:45 am
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    At first thought, Plant Trees…however there’s not enough ground water to sustain them…so then I thought, Plant Trees under the Fog Catchment…to eventually create an environment that will pull the water down and transform the ecosystem. Then I think – this could be an Irrigation System to grow food. Ya maybe farfetched…but possible. Possible that in these regions there’s not enough sunlight to grow anything….not sure ( I remember Freezing in San Fransisco in the middle of summer ). I love the Roof Top Idea! Again…for irrigation to grow a Roof Top Garden. Only You know….Thank you

    Reply
  • June 18, 2015 at 10:51 am
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    I would also be weary of metals in the water. I am considering designing a fog catcher prototype in Berkeley and spoke to some designers. They were under the impression that the fog carries mercury from ocean spray and that any fog will be unsuitable for drinking or irrigation. I will be testing the water quality in the prototype and recommend others do so as well.

    Reply
    • June 17, 2016 at 6:25 pm
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      Kit. I was wondering if you were able to set-up your prototype. And if so, would be interested to know your average yield in a 24-hour period and the quality of the water you captured. Thanks!

      Reply
  • March 11, 2016 at 11:25 am
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    So will this water be safe to drink then? Looks like the debate is out there. Would be nice to see some more research as its a great idea if it can indeed be rolled out.

    Reply
  • July 23, 2016 at 3:08 am
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    hi guys I am vitalis Haupindi from Luderitz I am in grade 8 and I am participating in a science fair competion whereby I am doing a project about collecting clean drinkable water from fog ,I would like you guys to give me advices on what type of materials attract fog the best

    Reply

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