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Bushcraft or BS: Filtering Water with a String

There’s no end to the harebrained ideas for purifying water in survival situations.

The video above is a test of one of the most egregious offenders of “survival hacks” gone wrong. This is the kind of tip that comes from non-experts who need “fluff” content to fill their new book.

As you can see in the video this survival hack has 2 main problems:

  1. Speed: you’d die of thirst waiting for this technique to work.
  2. Sanitation: String or paper towel will remove large contaminants like dirt and may lower turbidity (cloudiness) but will do very little to remove the pathogens (bacteria, fungus, protozoa, viruses) or chemical contaminants from the water. It’ll still need to be filtered or boiled to be safe to drink.

This survival tip is complete bullshit. This is a water pre-filtering technique at best, and a very bad one. You’d be better off pouring the water through a ball cap or bandana to remove large contaminants.

Best to leave this technique to middle school science lesson on capillary action.

Let us know what you think.

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28 thoughts on “Bushcraft or BS: Filtering Water with a String”

  1. While this may be very slow, if someone is hesitant about drinking dirty water, it could work over a period of time. One afterall, will not thirst to death in one day or two. Not the best way to do it, but it would give hope for the future. The water can be boiled after the dirt is gone.

    I have grown up in the woods pers se’, and do know how to filter out water, and to boil it to clean it. It can also be placed in a pot of sorts and let the sun evaporate it into a second container, which does purify it as well as filter it.

    The deal with the speed can be shortened up with having the first container somewhat higher than the catch container, and it is also called a “Wick System”. It is not absolutely impossible, perhaps a little improbable.

  2. Here is how I see it.The technique is only useful in so far as the water is basically transferred into another container leaving behind large particles of debris, either organic or inorganic material that may be floating in the water.

    Where it falls short, or can be see as a hokey method, is that the water was and is still tainted and polluted with chemicals or parasitic organisms and anything that it was poured over, sat in or that swam, ran or bathed in it. Or maybe died in it.

    Thus the water still requires purification by boiling, distillation, solar pasteurization, or chemical additives such as bleach or iodine. It would be faster and better to filter the water for debris with cloth (Bandanna, sock, etc., or a coffee filter) and then use a chemical agent. Of course distillation would be ideal if one had the stuff to do it and could make a fire.

  3. Rather than dismiss the technique outright, I suggest considering how it might be used. At the outset, however, I agree there are much better ways to filter water. I think using a gravel/sand/charcoal filter would be more efficient, even considering the time it takes to build one.
    1) Capillary action will only raise the water a limited amount, so having a wide, shallow container will work better than a deep container.
    2) Gravity is necessary to ‘pull’ the water down, so I would expect a longer ‘string’ to be more efficient than a shorter one. (Greater vertical distance from top of string to bottom)
    3) This is, as shown, a slow process. It isn’t something to quench ones thirst immediately. It could be used for a base camp or overnight replenishment as the first stage of filtering from a large source, assuming the height distance is possible.
    4) The flow rate should increase by using more strings. The paper towel mimics this by increasing the area, similar to using more strings.
    A system using these principles might work for taking water from a stagnant source and having it constantly pre-filtering to a larger container, in more of a base-camp setting. The biggest drawback I see is that the string will eventually clog with particles and have to be replaced (suboptimal) or cleaned. This might make sense if it works with string substitutes, such as bark fibers – again, as a pre-filter. In any case, if you have string, I don’t think using it as a water pre-filter is the best use for it.

    I’m not saying it’s a good idea, just considering the principles involved. I agree, there are much better ways to pre-filter water.

  4. I read premoistened cloth to filter out particulates saving your actual filter from clogging fast. Or clear water for boiling.
    I live near a river that has red clay in it most of the time. If I ever have to use it for drinking the rag might be what I use or the TRS survival shammie.

  5. The best way to filter water in extreme conditions is to pour through a filter of gravel, sand and charcoal (Or mesh / cloth) to remove larger impurities. Then boil the water for at least ten minutes. Although this method is crude it is probably the best method in extreme circumstances if you do not have a water purification system to hand. A few sips of your “Purified” water is recommended at first to ensure you have no extreme reaction. The amount can be incrementally raised and reactions monitored to minimise risk of extreme illness / eventual death.

  6. in all of my past 66 years (starting around the age of 10 ) you could count on one hand the number of times that I have carried more than one container. some were I – qt. and some were the back pack type, plus I don’t think I ever cared a cotton string.. filtering the big stuff can be done thru a piece of clothing or even a back pack. I depend on the tablets or the new filtering devices if and when I get out these days.
    think the string and jar is out because if it works it is way too slow at 2-3 drops an hour.e

  7. The tecnic shown in the video, have litle use in a situation of real need, in short time. Better use is for taking water from a source where the wather is not so abundant. But has it takes time to get a minimum quantity, only for taking the most possible, geting the most wather possible, from diferent sources.
    But, it´s not advisible to forget, that the string can and would have, patogenics elements that put the wather under the need of descontamination. So, this methode depends of the ever decontamination you can get. Even the most simple methodes, put attention for decontamination factor.
    Beeing sure that there are some ways to get “purified wather”, with more speed and garanty , I’ll use only in very restrictive situations.
    Surviving is more brain capacity and ability to materialize the thecnics, than equipement.
    Sorry for my english, but it’s not my birth language.
    Best regards

  8. I have taken cloth or netting and stuck it in a bucket of water and ran it to my potting plants and it will keep it watered but as for filtering it umm don’t think so but I also wet the whole cloth before I did this . Sitting water in the sun if hot enough will help purify it too but again takes a long time … Rocks sand and charcoal [ burnt wood from a fire ] will work then boil it . So I am with you this seems like BS hee hee and this is coming from a lady smiles.

  9. No mention of losses here by evaporation…far more water will evaporate on the way across than drip into the receptacle.
    I wish people would proofread before they send; even a great idea is compromised when the sender sounds ignorant

  10. I’d rather build a fire and use charcoal sand and grass , there’s always plastic bottles somewhere in the wild now a days. Besides I always carry a bandana , tee shirt etc. to use!

  11. I’ve made filters using old lge. Plastic pill containers by drilling small holes in the bottom , then two holes in the top for carrying string to attach around your neck or where ever, then put a layer of cotton in the bottom ,next go to a pet
    store where they have fish and get a small jar of activated charcoal and put in a layer of it in the container along with cotton on top. Now you have it when ever you head out fishing ,camping etc. I carry some along with a couple empty plastic bottles in the cars for boiling , remember you can always cut the top from a plastic bottle for use as a funnel ! I also stuff a few water proof matches in the bottle and take them out before using as a water filter now your prepared !

  12. Heard this one years ago and it nearly cost me and my wife our lives! Also agree works for pre filter of large contaminants very slowly, if you have that kind of time, but does nothing for Bacteria and Protozoa!
    Definitely Bullshit! Boiling and fine cloth still the best way to be sure!

  13. Dear Sirs:


    The string/cloth/paper towel filter idea has been around for a long time and some prepper wannabes take it as “Gospel” …. but, they do so without ever attempting it.

    As you wisely pointed out even if you get the dirt, lumps and swimmie things out, this technique DOES NOT remove the pathogens that will make you sick or even KILL YOU! The clearer water would still have to be boils at the very least, and in urban zones any chemical contamination would still remain, they don’t boil out.

    Thanks for demonstrating the pure BS of it.

    God Bless,
    Orrin M. Knutson
    Peace Officer/Search and Rescue Volunteer Retired
    Survival Author

  14. I think I will suck up the morning dew with my shirt or lick pine trees in the morning the string theory is a good laught

  15. I have used coffee filters as a pre-filter for really cloudy water.
    I then use a fine filter and then boil the water. I carry coffee filters in my field pack.

  16. I agree Bob, if that isn’t bullshit, it’s as close as you can get. Someone can live 3 days without water, experiencing horrible symptoms all along.I can think of 2 ways to filter water. 1. a rain barrel with a tarp over it and a very fine filter at the center to catch rain. 2. My way, a rain barrel again, but don’t bother with a tarp. That’s only the beginning. However much water you plan to use that day, boil it. Almost finished. A friend told me about a hack to make filters both stronger and last longer by adding a coffee filter to it. Last step, filter the water.I use Zero Water, but there are many filters out there.