Fog Collection As Sustainable Water Source

paulproteus writes: "Space.com has a new article up called 'Fog Collector.' It describes a $450 polypropylene net that is used to gather fog, and convert it into drinkable water. 'Fans of science fiction will recognize this idea from Dune.' The nets 'have replaced and surpassed the thready life vein of truckloads of water that once sustained a village near the Atacama Desert in northern Chile.' The article also describes the second International Conference on Fog and Fog Collection."

Comments

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[paulproteus]

I think that this URL affects many /. viewers, and should therefore be on the main site.

Why is this only on the Science subsite?!?

Re:Horizon (IIRC) had a story about these nets...

[cetan]

I knew I had seen this somewhere a long long time ago. The nets are used in some remote mountain areas that dont' get a lot of rain but get lots of fog. the people trap the moisture and it get's piped down the side of the mountain to their village. sheesh, that episode was years ago....

Interesting calculations

[jellisky]

It's actually truly amazing that you could get something sizable out of fog, but it actually makes some sense.
Here's some back of the envelope calculations that might be a bit convincing:
(Note: I'll be using standard scientific E notation. So, 6.4E+3 = 6400.)

The liquid water content of a dry fog is 5E-8 m^3(H2O)/m^3(air). This translates into 5E-4 L(H2O)/m^3(air).
Assume that we can collect a fog bank that's 10km x 10km x 10m (height). That would be 1E+9 m^3 of fog, or 5E+5 (or 500000) L of water in that region.
Even if we only could collect 1% of that, it's still 5000 L. Seriously, that's not too bad for that kind of area of land.
Problem is that evaproation would take back quite a bit of that if one isn't careful.
It's amazing how much water could be tapped from clouds of all sorts. Problem is, that those well-versed in the hydrological cycle will tell you that the water in the atmosphere is VERY small compared to that elsewhere in the world. (We're talking hundreths of percentages here.) Perhaps trying to figure out better ways of de-salinating ocean water should be a little more important.
Just my thoughts.

Re:Interesting calculations

[Louis_Wu]

Perhaps trying to figure out better ways of de-salinating ocean water should be a little more important.

Unless you live at 7000 feet, 500 miles from the nearest large body of water, and the water table is 2000 feet down.

Granted, these types of cases are rare, and de-salinization is very important, but the people who are working on this wouldn't be working on de-sal processes or plants. So they might as well do something to keep people in water.

Louis Wu

"One of life's hardest lessons is that life's lessons are hard to learn."

Effect on Environment?

[dmatos]

Don't get me wrong, I'm not an eco-terrorist or anything (actually, I loved the clip where the Russian loggers heaved a Greenpeace member off of their ship into the ocean :). However, are these fog nets large enough to have an effect on the surrounding environment? I know that fog banks are a critical part of the ecosystems on both sides of ridges. Is enough water being harvested to adversly affect anything?

It was different on Arrakis because any moisture they didn't collect would just be collected by the sand trout anyway. Here maybe it will make a difference.

Re:Effect on Environment?

[Mad Hughagi]

Well, it's estimated that up to 1% of clouds formed in the upper atmosphere are the result of jet trails, and there was some commotion about that, so I don't doubt there will be some kind of evironmental stirring about this application if it is considered to be implemented on any large scale.

The direct consequence of altering the density of water vapour in the atmosphere is that you will have appreciable temperature changes. Since water absorbs IR (the portion of the EM spectrum that accounts for most radiative heat) you could be reducing the ability of the atmosphere to maintain it's temperature. Whether or not this would be a serious temperature change is left to the reader to calculate.

I guess another aspect that you have mentioned is that fog banks provide the needed moisture for heavy rainfall areas (coast of BC) and that by reducing this you might be reducing the amount of precipitation in the area. The counterpoint to this is that you probably wouldn't be using these nets in wet rainfall areas anyways since the rain provides a water basin.

13,000 cubic *kilometers* of water in the air!

[salsbury]

According to some research I did for a paper, there are actually about 13,000 cubic kilometers of water resident in the air at any period in time. Details and numbers are here. This comes out to about 1/10th the total of all freshwater lakes on the planet, or 13 times as much as all the freshwater streams and rivers of earth.

The nice thing about pulling out of the atmosphere, is that it's a great automatic distribution system. There's water vapor blowing over most of the planet, most of the time. No need to truck it in or dam up reservoirs when it can be drawn from the air where it's needed.

One other person was asking about environmental impact. If you look at the diagram at the above URL, you'll see a great graphic of the hydrological cycle. There's so much water in constant motion on the planet, that any we took out of one place is being replaced someplace else. And since it's in gaseous form, when you draw it out in one place, you're creating a 'relatively dry' airspace for more water vapor to flow in towards you. Also, given the numbers in that graphic, you'll see that we couldn't really even begin to dent the amount of water in the atmosphere. Most of it falls directly back into the oceans, so there's plenty we could get from nature's own desalination process.

I also run a mailing list devoted to discussion of water topics like these. You can find info about it (and lots of other neat stuff) at the Reality Sculptors website.

Patrick Salsbury