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Thread: purify salt water

  1. #1
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    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.

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    Quote Originally Posted by tb-av View Post
    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?
    "I never learned from a man who agreed with me." Robert A. Heinlein

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    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.

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    Quote Originally Posted by AK47guy81 View Post
    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.

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    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.
    [SIGPIC][/SIGPIC]

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    If one needed to get fresh water from salt for an extended period, then steam distillation would be the way to go.

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    Quote Originally Posted by rero360 View Post
    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.

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    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.

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    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.

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    nice, good info.

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