[Paddlewise] Saltwater to Freshwater "Devices"

Speaking from experience, the best method I have found is to carry your
water with you, next best was distillation using fuel (a stove if you have
plenty of fuel or a firewood back-up if not), although I'd be prepared to
use other methods like a solar still, or pump as well.
A group of us were stuck on an island in Baja and held down for 3 days by
winds 35 to 40 mph winds (we measured) gusting to 55 mph. Late on the first
day we realized that if these winds lasted more than three or four days we
would be out of water. On the second day we spent all morning (a cooler time
to minimize sweating) digging a pit for a solar still. We threw in a lot of
salt water and covered it with a lightweight CLEAR plastic film (Clear not
Black--Black won't work--just gets hot and won't allow the evaporating water
inside the pit to condense on it). Had a pot in the bottom and even surgical
tubing down into the pot so we could drink directly out of it and not have
to open up the system to get the water out. We then carefully placed a large
smooth stone in the middle above the pot and waited and watched. The plastic
became covered with condensation, raising our hopes. Trickles started to run
down the plastic, but to our chagrin most of them broke loose too soon and
didn't make it into the pot. The plastic was vibrating due to the wind (and
pressure changes due to gusts) even though we had built an elaborate wind
break around it and not much wind reached the plastic. About 1/2 hour into
our little experiment that took all morning to set up the sand that had
blown into the top of the still combined with the motion of the plastic
ground a hole through the plastic and the rock and gritty dust/sand
collapsed into the catch pot with a sickening thud. Lesson #1: use much
heavier plastic than the lightweight (1/2 mil) painters dropcloth I happened
to have. Lesson number 2: You are unlikely to get this to work when the wind
is up even with more durable plastic. This is unfortunate since during
strong winds is the most likely the time you will be stuck somewhere on a
paddling trip.
Plan #2: build a moonshiner's still. Someone had a pressure cooker, we
hooked it up to my surgical tubing and fired up the stove. It worked a
little but not very well. We sought to improve it. I had a snorkel that fit
over the pressure relief valve, We cut the long tube off another paddler's
Bow float bag, it fit perfectly inside the snorkel tube and we taped the
other end of that 3 to 4 foot tube into a 1.5 liter medical bottle which we
stuck in a bath of sea water. We quickly heated the seawater but even when
it got very hot and we soon tired of changing it every few minutes we were
still making about a quart of water per hour this way and probably using
less than a pint of fuel per quart.
The water tasted like rubber from the hot snorkel tube but it was fresh and
palatable (although we never had to use it we carried it with us until we
got back to a water supply). Later I made a still from a backpackers
pressure cooker and some copper plumbing tubing that I could store coiled
inside the pressure cooker.
 I also got a Survivor 06 (the smallest of those fresh water makers under
discussion here) to test out. I tried it and it worked, but slowly enough so
that for all the work that went into it was quickly obvious it would be only
be suitable for backup survival. It also required careful maintenance, had a
limited life and needs to be returned to the factory periodically to have
the membrane replaced. It was hand operated but I though it would be far
better to make it foot operated so you could use your hands for other tasks
like holding and turning the pages of a book during the long hour of
pumping. I sent this device to Baja with others a couple of times to get
there opinion over the next couple of years. The unanimous conclusion was
"for survival mode only". I don't know the reason but on testing it after
the last user (a long trip) it no longer functioned. I haven't bothered to
get it repaired. Ed Gillet had two (I believe) of the larger hand operated
ones on his California to Hawaii kayak trip.  Since everything he had
powered by electricity eventually failed I suspect he's glad he had the hand
pump ones.
There is a spherical shaped military solar still that is designed to work
while floating in water but I have never seen one in operation.

Graham MacIntosh described using a tea kettle as the container for a still
and it was by far the best way he made water during his 3000 mile walk
around the coast of Baja (described in his book "Into a Desert Place"). It
almost killed him when it corroded out and became useless once when he
really needed it. Hot salt water is very corrosive.
I take at least a gallon a day. I store it in many containers so no one leak
or accident to a container will leave me wanting. Two liter soda bottles
work well. They are very tough and can be flattened to regain storage space
and can be blown back up if more water is found to refill them. They are
small enough to tuck into many leftover nooks and crannies between gear bags
and the hull. They can be easily moved around to get a level trim too.

Matt Broze
http://www.marinerkayaks.com

original message:
Date: Tue, 01 Feb 2000 19:40:52 -0800
From: Dave Kruger <dkruger_at_pacifier.com>
Subject: Re: [Paddlewise] Saltwater to Freshwater "Devices"
BaysideBob wrote:
>
> Speaking of "survival", does anyone have any info on distilling fresh from
> salt?
> I saw a website of a fellow who did it at the rate of one part fuel to one
> part freshwater distilled, not too effecient and no details as to how it
was
> done. Or perhaps solar stills?
Basically, to get the efficiency up, you have to make good use of the heat
from
the fuel by pre-warming the water entering the still pot with some of the
"waste" heat from the condensing phase. That is SOP on the oil patch or in a
refinery, where every calorie of waste heat is a few millicents lost, and
every
food Calorie is a penny lost. A practical thing when the operation is
stationary and will be used endlessly. Some arid countries do this with sea
water. Invariably, they have cheap fuel -- or, as in the Middle East, the
fuel
is "free:" in Saudi, natural gas has no market, so they just flare it off at
the well head. At that price, it pays to make fresh water from salt.
For we energy-poor sea kayakers, using a large surface-area unit which
exploits
the (low-grade) heat from the sun, and a condensing water source of coolness
(read: sea water as the condensing fluid) is the only really "efficient" and
practical method. Drawback: can't be done on the rolling deck of an enroute
sea kayak. Can be done ashore, with some setup time. Good to know for a
survival situation. I think NOLS has published some methods using black
plastic as the solar collector for the heat. A Web search should reveal some
tested techniques.
- --
Dave Kruger
Astoria, OR
chemist


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