

Fog-harvesting system could provide potable water for the world’s driest regions - interconnector
http://web.mit.edu/newsoffice/2013/how-to-get-fresh-water-out-of-thin-air-0830.html

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dalke
This title is a bit of an over-exaggeration. As the article says, "Systems to
make use of this airborne potable water already exist in at least 17 nations."
The title implies that it's relatively new technology.

For some historical background, an early fog harvesting project started in
Chile in 1987, and the success from that kicked off projects in other
countries. (Based on a cursory search I just did.)

The linked-to article then clarifies the importance of this new work: "But the
new research shows that their efficiency in a mild fog condition can be
improved by at least fivefold, making them far more feasible and practical
than existing versions."

~~~
schiffern
Fog harvesting's a lot older than that. The Bimbache people used a communal
fog-harvesting tree to provide water on an otherwise uninhabitable island in
what's now the Canary Islands. They led the drip lines to gravity-fed
channels, which directed water straight to their dwellings. Clever systems
like this demonstrate what we already knew — that indigenous people were (and
_are_ ) no dummies.

[http://en.wikipedia.org/wiki/Garo%C3%A9](http://en.wikipedia.org/wiki/Garo%C3%A9)

[http://archive.org/stream/mobot31753002257217#page/152/mode/...](http://archive.org/stream/mobot31753002257217#page/152/mode/2up/search/Canary)

~~~
dalke
Interesting! Though in reviewing the second link I find very little that was
definite. It recounts things second- and third-hand. Some claim a single tree
could provide water for 8,000 people and their animals, another said for 80
families. Some say it was a single tree, others from multiple trees.

You say "otherwise uninhabitable land", but Brown's 1910 guide book points out
that people lived there, grew grains, and pastured animals. As there are
"practically no springs", people needed to build cisterns to catch rainwater.
The translated Spanish document (from the last 1500s?) says there are three
streams on the island, and that the tree (which was not seen by the Spaniard)
is a third type of water source.

Since the 1910 inhabitants didn't use this tree as a water source, I presume
that cisterns and those small springs were enough for them, and so would have
been enough for the Bimbache.

For that matter, how did the first Bimbache live there if it was otherwise
uninhabitable. Did they need to find the tree(s) before they could settle?

You write "which directed water straight to their dwellings" but Duret (1605)
writes that the tanks of water were at the foot of the tree, and that the
remnants from the 1612 storm were still there in 1753. But I don't see
anything in those accounts about channels or pipes leading the water to
people's homes. (The Wikipedia page says "The Bimbaches later filled water
chaffs and water was transported to towns to all parts of the island", but as
part of a legend, and without a citation.)

This is not me rejecting the idea that fog collection was done before the
1980s. Indeed, the Wikipedia page for 'Fog collection' lists several "natural
or assisted" collection methods. Nor am I rejecting the idea that the Bimbache
used trees as a fog collector.

What I'm commenting on is that the information I've read is suggestive, but
not definitive, and that what I've read doesn't fully match with what you
wrote here.

What I would like to see might include measurements of water run-off from one
of those trees, growing in the same area and archeological evidence of an
irrigation system, rather than carrying water from cisterns.

BTW, I really like one of the accounts in that second link about that sense of
astonishment by the British scientists at Cape Town who, 110 years ago or so,
found out that the fog around Table mountain provides a huge amount of water.

~~~
schiffern
Yes, it seems I overstated their dependence somewhat. Obviously water is
important, so you want redundant systems so you have water in both rainy and
dry times. Multiple systems on different scales (family, village, and island)
is a possible explanation for the disparate accounts. Even today most human
systems come in different scales.

> _Since the 1910 inhabitants didn 't use this tree as a water source, I
> presume that cisterns and those small springs were enough for them, and so
> would have been enough for the Bimbache._

That depends on how many inhabitants and what they're doing. I can't find
historical population numbers, unfortunately. Today's population of ~10,000
uses industrial desalination.

> _But I don 't see anything in those accounts about channels or pipes leading
> the water to people's homes._

Check out pp 156: "It falls into a pond made of brick, floored with stones
very tight, by pipes of lead conveyed from the tree to it, _and thence divided
into several ponds through all the island_. They which dwell up-hill fetch it
in barrels."

All in all, a fascinating technology. It's amusing how the western accounts
attribute everything to luck/God, but that's colonialism for ya. ;)

(If you can't tell, I'm a fan of Clarke's [revised] Third Law, "Any
sufficiently advanced technology is indistinguishable from nature." It's even
been proposed as a solution to the Fermi paradox:
[http://www.nextnature.net/2012/02/any-sufficiently-
advanced-...](http://www.nextnature.net/2012/02/any-sufficiently-advanced-
civilization-is-indistinguishable-from-nature/))

~~~
dalke
I discounted the telling on p156 because the population size (enough water for
8,000 people and 100,000 animals), the description of the tree (withered in
the day and dropping at night), and being able to fill 20,000 tuns (about
1,000 L/tun) in a single day.

I also wonder how they were able to get the lead for those pipe. Other reports
imply that there was little contact between the islands, so they likely didn't
trade for all that material. Figure a 4 cm across, and 5 km of pipe gives 6
cubic meters of lead or 70 tons of lead, which is a full load on a Spanish
caravel of the 1400s. And I think I'm underestimating that number.

I tried to find more historical information. The Spanish Wikipedia page points
out that a well with brackish water was dug between 1702 and 1704, as part of
a search to find drinkable water near the coast. It also commented that
Columbus stopped there on his voyages to the Americas.

So I looked up a translation of the log of his first voyage. The entry for 9
Aug 1492 says:

> The Admiral says that many honourable Spaniards, inhabitants of the island
> of Hierro, swore that they were on Gomera with Dofia Inez Peraza, mother of
> Guillen Peraza, who was afterward the first Count of Gomera, and that each
> year they saw land to the west of the Canaries

"Many" is not helpful, but at least a few hundred people on the island?

I looked backwards in time. Jean IV de Béthencourt conquered the Canaries for
Spain in the early 1400. "There was no resistance offered by the scattered
guanche population who were largely sold as slaves" says Wikipedia. Nice guy.

Your best bet I think is to look for records in Spanish. Oh! I found
"Conquista y antiguedades de las islas de Gran Canaria y su descripcion: con
muchas advertencias de sus privilegios, conquistadores, pobladores, y otras
particularidades en la muy poderosa isla de Tenerife", dated 1676,

My Spanish is rather poor, but I think page 59 of
[http://books.google.com/books?id=cKvrI2UF-
LgC&pg=PA59&img=1&...](http://books.google.com/books?id=cKvrI2UF-
LgC&pg=PA59&img=1&zoom=3&hl=en&sig=ACfU3U08RZ14esuFu7FPzYidt6kbigs3tg&ci=486%2C40%2C378%2C339&edge=0)
says there were 1,800 inhabitants of El Hierro.

Here's what I could copy from that text (updating the syntax to more modern
Spanish):

La isla del Hierro esta diez y ocho leguas de Tenerife, es pequeña, tiene su
Villa con buena Parroquia, y dos Beneficiados, que acuden a toda la isla y
algunos Capellanes; ay vn Conaento de San Francisco; cogese much trigo, y
ganado; rendra la isla mil y ochocientos vecinos, y muchos principales.

Here's my+Google's translation:

El Hierro is eighteen leagues from Tenerife, is small, has its Villa with good
parish, and two Beneficiaries, who flock to the island and some chaplains;
(also a convent of??) St. Francis; grows(?) much wheat, and cattle; the island
(has?) 1,800 residents, and many (bosses? people who can represent your
business interest?).

So, a 1670 population of about 1,800 people, under the Spanish crown, and
before the 1702 well. I think this find greatly weakens the hypothesis that
fog collection was necessary in order for a group of up to 2,000 people, and
that they could have survived on the limited springs and cistern storage of
rain water.

~~~
schiffern
I am unable to read the text you linked to. :(

Sounds like the Bimbache people could support 4x the population that the
Spanish could (8,000 vs. 2,000), which makes sense (water being the limiting
resource in that landscape).

Why discount pp156 again? The numbers are perfectly doable with a carefully
placed tree that uses the surrounding landscape to funnel fog to it.

Lead pipes wouldn't be needed for the entire length — clay-lined spillways
would more than suffice. I read it as using lead _just to the cistern_.

Great research, thanks!

~~~
dalke
Before starting, let me say that I've found this conversation very
interesting. Thank you for participating in it with me.

I discounted it for several reasons.

1) There's no corroborating evidence that the population was that high. I
haven't found anything more than "sparse", but
[http://www.sharprazor.com/palma-history.htm](http://www.sharprazor.com/palma-
history.htm) gives some of the history of La Palma:

> The Guanches named their island Benahoare, and divided it into 12 kingdoms,
> each with its own ruler. Estimates of the Guanche population at the time of
> the conquest range from 1200 to over 4000.

La Palma is over twice as big as El Hierro (708.32 km2 vs. 278 km2) and it
seems to support better agriculture and easier access to the sea. I find it
difficult to believe that the population density of El Hierro was at least 4x
more than that La Palma, when the best I can find is that the population of El
Hierro was "sparse."

2) The numbers I see for modern fog harvesting are about 5 liters per square
meter per day. The account says that a tree could fill 20,000 tuns/day, which
is about 20 million liters. This needs about 4 million square meters. Assuming
an 80 meter high tree and 32 meters across (the size of a larger redwood tree)
gives a cross section of 2,500 sq. meters. There's no way these numbers are
close to compatible.

3) Let's assume the tree can capture an excess of 1 liter per sq. meter cross
section, even though there's no evidence that any tree can do that. Let's
assume also that a single tree has a cross section of 2,500 sq. meters. That's
2,500 liters per day. Not bad, but people need about 2 liters per day as a
minimum - and more if they do much activity. Even in this unlikely and extreme
case, that's only enough to provide basic water needs for 1,000 people.

The WHO says "a minimum of 7.5 litres per capita per day will meet the
requirements of most people under most conditions", so that's 330 people. And
no animals.

(Another estimate is to look at the amount of water in fog. A cloud has about
0.5 g of water/cubic meter. However, this is too complex for me to figure out,
because I don't know how much water you can extract with fog mining, I don't
know what a tree or other plant can extract, I don't the wind speed, and I
don't know the capture area.)

4) Why use lead pipes to lead to the cistern? Since clay is good enough for
the cisterns, what's the advantage of using lead for those pipes?

Since each individual detail is not trustworthy, I find it hard to put any
faith in the overall account. How are you certain that it isn't a tall tale,
with little to no basis in reality?

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sologoub
If used on a large scale, I wonder how this would affect the environment
around the collection sites. As is now, the fog goes somewhere and I'm sure
some organisms rely on it getting to where it's going.

If the water is collected with enough efficiency, there could be significant
unforeseen consequences.

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Core-TX
Hmmm, that reminds of Arakis. Are they called windtraps ? ;)

~~~
bjterry
Or moisture vaporators in Star Wars, which Luke's uncle and aunt owned.

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tocomment
If h2o is heavier than other components of air like o2 and nitrogen why can't
we just run air through a giant centrifuge to get the water out?

~~~
aaron695
Generally with these schemes the fog is from the ocean so you have unlimited
saltwater to desalinate, the idea is to get water with little energy cost.

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ForFreedom
That would not be applicable in desert regions.

~~~
NotHereNotThere
How so? From reading around a bit, I found several sources that indicate fog
is present in the desert.

~~~
lutusp
There's no basis for the idea that there is never fog in the desert, as long
as there's sufficient water vapor. But a very dry desert climate cannot fog up
for lack of water vapor.

Remember that fog forms when temperature and dew point collide. But without
water vapor, there's no meaningful dew point.

[http://en.wikipedia.org/wiki/Dew_point](http://en.wikipedia.org/wiki/Dew_point)

Quote: "The dew point is the temperature below which the water vapor in a
volume of humid air at a given constant barometric pressure will condense into
liquid water at the same rate at which it evaporates."

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cz20xx
Tatooine

