Desalination at sea or on the coast

Bill Siegle

Bill Siegle

Knifemaker / Craftsman / Service Provider
Joined
Oct 3, 2000
Messages
6,955
Sooooo with the plethora of disaster shows on Discovery Channel(and others) I am seeing a lot of episodes devoted to being stranded on or near salt water. What is available or how can one remove the salt from sea water for drinking? I was theorizing a solar still might work by using a large pot to hold sea water and a smaller pot onside that to catch evaporated water caught on the plastic sheet. I saw a similar device at a local Science museum that had a fresh water collection area built into the base of a clear plastic cone that you would set over a pot of sea water. Am also thinking cooking the water and catching the steam would work but at sea you would need a stove as I assume you wouldn't want to burn your decking :) Any other ideas?
 
I see the solar still a lot but I would highly doubt that i would have plastic wrap with no holes on me and a pot. I heard that turtle blood is safe to drink, but I am not too sure about that.
 
One episode of Ray Mears, the one on Military survival, showed the Brits training along the coast. They had created an actual still from food tins and such. I assume this is a tested design and part of their military survival doctrine but I've never seen it in any literature.

The desalinators that I've seen are bulky and expensive. Does anybody know of one that isn't?

Many of the stories of long-term survival at sea depend upon rainwater for drinkable water.
 
Ive read this recently

"Another source of liquid sufficient to sustain life at sea, when fresh water has ceased to be available, is from the flesh of fish. The fish are diced, and the small portions of flesh placed in a piece of cotton cloth and the moisture wrung out. This moisture from sea fish is not in itself excessively salty, and can sustain life for a long period." -The ten bush craft books by Richard Graves
Downloadable here
 
Bill, right down the street in your state is US Tactical Supply - Albany. They sell a small portable unit that does exactly what you're looking for...if you don't see it on-line call them. My son works for this company and I was looking at them the other day when I was visiting him.

Their largest customer is the military and they sell a ton of stuff on line or via the phone. Last year they opened up a nice store front.
 
While not desalination per se, this is a method that's gotten a fair bit of attention lately and seems very innovative in it's pure simplicity, and could potentially work in a survival situation. The "Fog Quest" system is a fog water harvesting system that uses a double layer of overlapping nylon mesh screen nets. I recently saw a documentary on this and was amazed. One square meter of mesh can collect up to 5 litres of fresh pure drinking water per day. The downside to this is that it does require moist air to operate so it would not work just anywhere. It has proven to work well in the coastal regions or Peru and Chile where you have deserts existing at the coast and very moist air blowing in off the ocean (since I began monitoring it with my Kestrel two months ago the humidity in Lima has averaged about 85%, and yet the Peruvian coast is for the most part a barren desert).


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Long distance sailors use RO desalinators, but there are some portable 'lifeboat desalinators' available. Their output is fairly low, as you have to use hand pressure to pressurize the membrane. Given that RO membranes typically see 1500-2000 psi, it's easy to see that it would take a lot of pumping. That being said, I've seen them in kits but never actually used one.

I've read about people using their sails in both fog and rain to collect water like the Fog Quest idea. There are a bunch of books by Larry and Lyn Pardey that deal with offshore cruising and have a lot of tips that would be helpful to anyone who has to preserve and ration their supplies for a long time. A good one on food storage is Care and Feeding of Sailing Crew.

I've made solar stills and this is just my own experiences with them, but the only way I've found to get a decent output is to lift off the top sheet periodically and collect the condensation manually. You get way more volume that way than from just leaving it....unless you set up more than one I guess.

I'm trying to make a backpacker's still myself actually. Tried a couple different ways, but I'm beginning to think that immersing the coil in a cold water bath is the way to go (versus burying it).
 
Here you go, Bill.... $2000, but produces 1.2 gal/hr of use.

http://www.landfallnavigation.com/-sas35.html

http://www.landfallnavigation.com/ps40.html This one is slightly larger, but works on 12V, so to some extent it would depend on how portable you want to be.

If "highly portable" isn't one of your needs, you could always spend another grand or so on a solar panel that produces 10amps, have your watermaker run all day, and have power to spare.
 
Bill - are you talking about starting with nothing or in a situation where you could prepare?

From nothing - depending on geography of course; rain and dew collection will probably be the most efficient. A compressed sponge in a zip lock can be a useful tool in some environments.

I have made a solar still and don't see the value unless it was for long term use and in an ideal environment of production. This is purely a guess, but based on the one I made (in great conditions), it would take two to three days MINIMUM to get a return on the energy and perspiration spent in construction.

If you had something - I would build a distiller assuming you have fuel wood. (1) Take a large pot with lid (not flat), fill partway with seawater (2) Suspend smaller pot inside larger pot where it is lower than the top of the larger pot. Make sure to get it in the middle. (3) Take lid of larger pot and turn upside down and use as cover of larger pot. Typically the lids are conical and by turning it upside down the steam will caught as distilled water will run down and drip into the smaller suspended pot (kinda like a solar still).
 
Those portable yacht desalinators are nice but pricey. I was looking into getting one, then decided the between $600 and $2000 wasn't in my budget. I'd still (pun) like to save up for one since I am starting to do a lot of marine work on boats.

I recall one of the survivor tips out there, was to dig a hole behind the dunes on a coast and you can usually encounter freshwater streaming into the ocean. Treat as you would any source of freshwater. That or start up a cocunut collection.

Actually I think the freshwater source - around coastal zones is an issue that gets too little play here on the forums!
 
"Bill - are you talking about starting with nothing or in a situation where you could prepare?"

Guess a little of both. Maybe an in between plan of carrying minimal supplies and mix em with a little knowledge :) I read somewhere of a sailor lost at sea for many months and he knew that fish eyes were a good source of water. He used the fish eyes and water catching to stay hydrated.Really I don't spend any real time at the ocean but it is one knowledge base I know I would be lacking in if stuck out there. I would rather be lost than lost and dehydrated :)
 
Great topic! Very applicable to me since I'll be spending some time cruising the coast this summer 'primitive style'.

Right now, I'm just planning on venturing inland in search of fresh water. A reliable backup involving sea-water would be nice, but I can't imagine one happening - I'd like to do this with a minimum of tools - meaning no pots that I couldn't make myself. Using a water bottle inside of a burned-out wood pot with pine boughs as condensers may work, but will definitely take experimentation before actually heading out.
 
A couple of simple clear plastic bottles put together with a little bit of tape will work. Won't make a lot of water quickly but it does work. And ofcourse it only works if you have plenty of sun. It's really a method I've seen used in the desert to get drinkable water out of your urine.

You lay it on the side and cover the empty bottle and let the other one heaty up in the sun.

I don't have time now, I have to go work at the ranch, but if anyone wants a photo of this very simple idea I can make one or two easily and take a photo a little bit later.
 
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