View Full Version : purify salt water
Was just reading another thread and got to thinking. If you live closer to rivers and the bay than say the mountains,,,, what is a reasonable procedure for getting pure water.
The thread in question was about the Katadyn Pocket. That's great for say mountain stream water or maybe high up a river but what if you were near where the rivers empty to the Ches. bay or further up but still in salt or brackish water.
Also is there any kind of test to determine how salty the water is.
I see Katadyn has desalinaters but damn that's $1K. I thought the Pocket was expensive at $250.
Seems like there is no easy solution.
Was just reading another thread and got to thinking. If you live closer to rivers and the bay than say the mountains,,,, what is a reasonable procedure for getting pure water.
The thread in question was about the Katadyn Pocket. That's great for say mountain stream water or maybe high up a river but what if you were near where the rivers empty to the Ches. bay or further up but still in salt or brackish water.
Also is there any kind of test to determine how salty the water is.
I see Katadyn has desalinaters but damn that's $1K. I thought the Pocket was expensive at $250.
Seems like there is no easy solution.
I want to say, something like a battery, wires, and two metal sticks might do it.
Also, boiling and condensing?
Boil salt water with a platic sheet tented over the top at an angle. The steam will be pure and condense on the sheet and eventually run down(hence the angle), collect the purified water in a container under the bottom tip of the plastic sheet.
Salt water is the hardest on filters, avoid using it in your regular filter systems except as a last resort.
Google how to make a homemade dowsing device and you can dig up your own fresh water.
Boil salt water with a platic sheet tented over the top at an angle. The steam will be pure and condense on the sheet and eventually run down(hence the angle), collect the purified water in a container under the bottom tip of the plastic sheet.
Salt water is the hardest on filters, avoid using it in your regular filter systems except as a last resort.
Google how to make a homemade dowsing device and you can dig up your own fresh water.
Dowsing is an old-wives tale that has been thoroughly dispelled.
Also salt water isn't just hard on the filters, filters won't filter out the salt because the pore size is simply too large to work with an ionic solution like salt water. Using a standard filter (such as a Katadyn Pocket) will only produce filtered salt water.
OP, to generate potable water from salt/brackish water you have basically two routes, distillation and reverse osmosis. Desalinators are almost exclusively the latter, and yeah, they are expensive. You can use evaporative methods but the flow-rate is generally pretty low.
I know it would be labor intensive and require a fair amount of fuel, but wouldn't a still be a good method of boiling the salt water and collecting the water vapor? I imagine it would be a bit more efficient long term than the plastic sheet method.
If one needed to get fresh water from salt for an extended period, then steam distillation would be the way to go.
I know it would be labor intensive and require a fair amount of fuel, but wouldn't a still be a good method of boiling the salt water and collecting the water vapor? I imagine it would be a bit more efficient long term than the plastic sheet method.
Boiling sea water and having it consense on plastic is a still. Instead of the vapor condensing on the inside of some type of condenser, it's condensing on the plastic. No difference, except a true still would be much more efficient since you wouldn't lose as much water vapor, so yes, it would require less fuel per unit of purified water.
Anchor Zero Six
11-26-12, 17:26
Water under vacuum boils at a much lower temp than at ambi atmosphere which would help maximize fuel use for a boiler/condenser desalination set up.
Also consider waste heat applications that could be harnessed such as the exhaust from a generator. Lots of stuff we operate routinely give off temps capable of boiling water under vacuum, trick is putting together a system to harness it.
One fairly common system once used by the Navy was to use the jacket water from the diesel generators to flash the brine water into steam at about 160 degrees F.
I live in south Florida and we keep a desalinator I our BOB simply because we are literally surrounded by salt water wherever we go. They have their pros and cons...
If you go this route, keep in mind that they use membranes, not filters... You need to keep them moist, they are fragile as hell and ridiculously expensive. The membrane for our $800 filter costs $400 and you must absolutely have at least one spare. A microscopic tear and its useless.
Also, at best, we get half a liter per hour with constant pumping. There are electic versions, but I assume that if we are desalinating salt water, things have gotten bad enough that electricity may be unavailable, so I wouldn't bother with them.
xrayoneone
01-05-13, 22:38
Also if it is a scenario where you do not have the means to boil the salt water you can set up a solar still. With the salt water in a small puddle place a cup in the center of the puddle that is taller than the puddle is deep. Place a plastic sheet over the puddle, anchor and seal securely and then place a small rock or other weight in the center of the plastic. The sun/heat will cause the salt water to evaporate, condensation will form on the sheet then run to the center and collect in the cup.
It takes a long time. I've tried it for shits and grins and it worked okay but you would probably die of thirst with the out put of this thing.
http://www.landfallnavigation.com/memss.html?cmp=froogle&kw=memss&utm_source=memss&utm_medium=shopping%2Bengine&utm_campaign=froogle
Have not used it, but have been told that something similar is still issued by the Navy.
Allen
whiskey lake
04-05-13, 16:34
Generally speaking (exceptions to every rule) it is almost impossible to desalinate enough water manually to last long term. The energy expended in boiling and collecting the steam is counter productive. You need a pretty complex operation to gather enough water.
Reverse osmosis would work, but salt water is really hard on the membranes. RO's also require a pump (electricity availability) to provide the high water pressure for the RO to work.
Easiest in the field way to provide safe water is distilling. If I had enough pots, tubing and plumbing fittings, I am sure I could cobble something together. Boiling will kill anything in the water, all solids and salts stay behind in the boiler and the steam leaves it through tubing or piping.
An air cooled coil of tubing will condense your pure water into a container.
The biggest problem is a safe boiler, or a way to remove it from the heat if the pressure gets too high. Boiling pressure vessels will explode if you don't have things right. As your pot boils off you need a way to add more water to it and also get rid of the concentrated "brine". Pretty doable, but it won't be a very portable set up.
The other problem with a distilling operation is smoke/odor from your fire attracting attention. You would also need close proximity to the water source and a steady fuel supply.
http://en.wikipedia.org/wiki/Solar_still
The one thing I have against solar stills is the low volume, plus the OP says he is in the Chesapeake Bay area, cloudy days and winter time will affect production or make them useless.
I made a few solar stills, one using a hole in the ground and a rock on plastic, made a half a cup of water in a day. With the scouts, we made one using a kiddie pool, and distilled off a quart in about 4 hours of sunshine.
Also is there any kind of test to determine how salty the water is.
Short of buying expensive lab equipment to determine exactly which salts are present? The easiest is one of those pocket TDS meters, a decent one is usually around $100. It won't tell you specifically salt content, but will give you ALL dissolved solids in the water. Usually anything below 500 is safe to drink solids wise, but will require chlorination.
One of those would give you a good relative idea of how "hard" the water is. It could mean the difference between adding some chlorine to low TDS water to kill any bugs, to having a very high reading and looking at having to distill it to make it drinkable.
If you specifically want to see salt content, I know some pet stores have hydrometers and other test equipment for salt water aquariums. That stuff is pretty cheap compared to lab quality stuff.
Here is a link to the EPA on drinking water standards and the maximums of contaminants that can be in water, pretty good definitions at the bottom also (scroll down): http://water.epa.gov/drink/contaminants/index.cfm
The one thing I have against solar stills is the low volume, plus the OP says he is in the Chesapeake Bay area, cloudy days and winter time will affect production or make them useless.
I made a few solar stills, one using a hole in the ground and a rock on plastic, made a half a cup of water in a day. With the scouts, we made one using a kiddie pool, and distilled off a quart in about 4 hours of sunshine.
http://en.m.wikipedia.org/wiki/Water_Pyramid
Scale it up. 1000l per day!
calebgriffin31
06-15-13, 23:28
Another thing with the solar stills. They do have their place. Although one still will not produce the amount of water necessary, multiple stills can. If you are digging holes for stills, you are obviously staying in that area for an extended period of time and can dig more than one still. Additionally, if some sort of tubing is placed in the collection device, the water can be removed from the still without having to disassemble the still.
if you have time and opportunity to make a solar still then why not just set up a system for distillation? you could boil the water and pipe it into a condenser of some sort and make distilled water.
https://en.wikipedia.org/wiki/Distillation
Distillation is your best bet. As others have stated. Solar or otherwise.
You can also use DE to filter salt out as well. I cannot locate the info on this currently, but will try to locate the info and post it at a later date.
Basic diatomacious earth filters can be found in homebrew supply shops and online that would work for this- using the proper DE.
Basically you can use the ground/soil to filter out the salt and collect the ground (Desalinated) water by digging a trench or setting up a mini well with hand pump.
Once lockheed brings "Perforene" to the market, RO filtering of salt water will be much more realistic and effective without such high amounts of pressure needed to push the water through the membrane- making RO systems small/portable enough to be used in survival situations.
Have no idea when it will be brought to market though...
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