How do you make an effective water filter using the natural elements of the great outdoors?

Suppose your only source of water was dirty and questionable at best. How could you make it potable without having to boil it and using only what mother nature has to provide?

I've never made one before, but I imagine it involves sand to filter out the grits, and probably charcoal to absorb the nastiness, as well as a couple other layers for reasons; like herbs that may be effective in killing microbials or some other form of alchemy that will make it safer to drink.

How do you make your own water filter when you're in a desperate situation?

  • Related: What are the different methods to purify water?, but making your own filter isn't one of the answers.
    – ShemSeger
    Commented Jul 28, 2016 at 15:01
  • Also Related: What backwoods trick to get pure water produces the most safe water?, but I want to filter the water, not distill it.
    – ShemSeger
    Commented Jul 28, 2016 at 15:03
  • What level of filtration are you comfortable with? Some virus' and something like mercury are very difficult to filter without nano filters which you can't produce without sophisticated equipment
    – user2766
    Commented Jul 28, 2016 at 15:50
  • Isn't this going to depend on what you mean by 'dirty' and what you think it's contaminated with? Commented Jul 28, 2016 at 16:15
  • 1
    @Liam, people drank water long before sophisticated equipment ever existed. I'm comfortable drinking water straight out of the creeks and streams. I've never used a water filter before, I'm just curious because of this question: outdoors.stackexchange.com/questions/13363/…
    – ShemSeger
    Commented Jul 28, 2016 at 17:36

3 Answers 3


Gravity Filters

Cone Filter

Much like Charlie's gravity filter in a bottle, this filter is essentially the same, only using a cone of tree bark in place of the bottle, and using extra filtration layers instead of a coffee filter or bit of cloth:

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Tripod Filter

Using a shirt, or bag with a hole in the bottom, or whatever bits of material you can spare, you can set up a tripod filter as shown below:

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Images: Pinterest, of all places...

These filters appear to only be effective at cleaning the water of dirt and debris, boiling the water is still recommended for purifying the water and killing anything that might make it through your filter, though any poisons should be mostly absorbed by the charcoal.

What remains to be discovered is what could potentially be used in either of these systems to purify the water as much as possible without boiling.

Filtration Layers

The following are layers you can include in your filter, and what they accomplish:

  • Grass: Filters out floaties, larger debris, and works as a permeable layer to support sand and charcoal.
  • Pebbles: Remove larger grits like sticks, leaves, gravel, small stones, etc.
  • Gravel: Permeable layer that packs well, good base layer for sand and charcoal, also filter larger particles.
  • Sand: Filter out smaller grits, sand, etc.
  • Ground Charcoal: Filter out finest particles, as well as some toxins/poisons (absorbed by carbon), will lose it's ability to absorb toxins with use.
  • Twigs: Plug bottom of cone filter so other layers don't pour out bottom.

Here is what I have found for a very basic set up with a cheap water bottle. The water will be pored through the top through gravel, sand, charcoal and finally either a screen or another mechanism like a hankerchief to prevent the filtering substances from getting into the water.

Like this,

|    |
  • | = Water bottle edge
  • G = Gravel
  • S = Sand
  • C = Charcoal
  • 0 = Screen or cloth

For more information I would suggest this instructable.

  • 1
    Screen and cloth are usually not considered "what mother nature has to provide" nor is a water bottle. Maybe replace the water bottle with a bark cone and the screen with moss. Commented Jul 29, 2016 at 9:58
  • I'd add to this, at least in Europe, a layer of sphagnum moss, which has natural disinfectant properties. Be aware, however, that it's a protected species in some countries.
    – flith
    Commented Jul 29, 2016 at 11:47
  • 1
    @filth I'm pretty sure human beings count as a protected species as well. All the rules go out the window when it comes to preserving your own life.
    – ShemSeger
    Commented Jul 29, 2016 at 14:34
  • 1
    @JamesJenkins You may not have a bottle on you, but at the very least I would hope you're wearing clothing, a bit of cloth off your shirt would suffice here I imagine. But it would be difficult if you didn't at least have a bottle.
    – ShemSeger
    Commented Jul 29, 2016 at 14:36
  • 2
    Just a reminder, for those who night be inclined to idly practice making such a filter. Many exceptions to the rules are permitted in survival situations, but are frowned upon when used merely for fun or for practice.
    – flith
    Commented Jul 29, 2016 at 14:38

Define dirty. The question says potable. The stuff that will hurt you requires very fine filtration that I don't think is feasible using natural elements. Filters for protozoan cysts and bacteria typically filter to 0.2 microns

Yes you can filter larger particulate matter (e.g. dirt) but that is not (typically) the dangerous stuff.

Is Water Treatment Even Necessary?
Q: Why do I need to treat water in wilderness areas?

A: Regardless of how pure water may look, any water source on the planet could be tainted with microscopic waterborne pathogens—disease-causing pests that, if ingested, could cause severe diarrhea, cramps, vomiting and fever.

Recent research, though, suggests that wilderness water at higher elevations is much cleaner than previously believed. Some experts argue that the blame for intestinal infections is more often traceable to preexisting conditions and lax sanitation, particularly unwashed hands.

Q: What's in wilderness water that can affect me?

A: Three groups of waterborne critters are most commonly linked to water-related illness:

  • Protozoan cysts (Cryptosporidium parvum, Giardia lamblia). Tiny (1 to 300 microns; 1 micron = one-millionth of a meter).
  • Bacteria (Escherichia coli, or E. coli, Salmonella, Campylobacter jejuni, Yersinia entercolitica, Leptospira interrogans and many others). Very tiny (0.1 to 10 microns).
  • Viruses (hepatitis A, rotavirus, enterovirus, norovirus, Norwalk virus). Exceptionally tiny (0.005 to 0.1 micron). Viruses are rarely found in North American wilderness waters. Only purifiers (not filters) eliminate viruses.
  • 2
    This doesn't answer the question. There's nothing in this answer about making a filter, or purifier.
    – ShemSeger
    Commented Aug 21, 2016 at 16:36
  • @ShemSeger The question states potable. "How could you make it potable without having to boil it and using only what mother nature has to provide?" en.wikipedia.org/wiki/Drinking_water Clearly I feel that pointing out it is not realistic is an answer. If you feel differently then fine.
    – paparazzo
    Commented Aug 21, 2016 at 16:45
  • 3
    This does answer the question and is the right answer. There is no easy way to make safe potable water using resources available in the forest without boiling it. You can make the water look cleaner and maybe extract some contaminants with the filtration system described in the other answers, but you can't eliminate pathogenic protozoa, bacteria and viruses. Commented Jul 1, 2019 at 15:41

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