How to Make a Field-Expedient Water Filter

by Erich

We all know how important water is in a survival situation. Without it, you don’t stand to last long.

One question I get on this blog from time to time is:

“If I were stuck out in the bush how would I go about making a field-expedient or homemade version of a water filter similar to the commercial varieties made by companies like Katadyn or Berkey.”

I assume they mean making a filter that can eliminate biological nasties like Cryptosporidium or Giardia.

If that’s what you’re after, boiling is the only tried and true method of water purification out in the bush.

The Limitations and Uses of a Field-Expedient Water Filter

In reality, there is no way to get a field-expedient water filter to replicate the filtration performance (in terms of microorganisms filtered out) that you’d get out of a commercial one, but it DEFINITELY doesn’t mean these filters are useless.

In fact, if you plan on using the boiling method with dirty, stagnant water, you’ll have some nasty tasting and discolored water to deal with (even if it is “purified”).

And this, my friends, is where a field-expedient filter would come in real handy.

How to Make a Field-Expedient Water Filter

So, how do you make one and how effective is it really, and how do I make one?

Well, I just uploaded a video to show you how easily it’s done (click on the link or watch below):

How to Make a Field-Expedient (aka BushCraft) Water Filter

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Comment by Joe
2013-08-30 22:48:39

My comment is actually a question. would the charcoal be wood ash that is the same as what you would make lye with?

Comment by woody
2013-08-30 22:59:20

How long did it take to process that pint?
Why didn’t you use sand as a component to the filter (assuming some was available at the creek)?
You said the pint was ready to drink, but you meant AFTER boiling it, or was it literally safe after the simple filtration?

Comment by Tactical Intelligence
2013-08-30 23:20:35


The charcoal portion is the black, solid stuff similar to a charcoal briquette that you’d use in a BBQ stove. The wood ash tends to be the white to brown “fluffy” powder (you don’t want to use that).

– Erich

Comment by Tactical Intelligence
2013-08-30 23:24:25


Good question. It was actually a 1-quart size mason jar. I didn’t time it but it seemed to be around 30 min to process (perhaps a bit more?).

As for the other question, yes meant AFTER boiling it. I’m sure this filter would reduce some of the microorganisms but most would likely get through and for that reason you’d need to boil it (or use the SODIS method if you had a jar or clear plastic bottle).

Hope that helps,

– Erich

Comment by carol miles
2013-08-30 23:55:16

Great Idea! I love your video;s, down to earth and easy to understand. Coffee filters would work great I think, I always have some in car and in purse, as I can always boil water and make a cup of coffee, if in hotels, or camping. Keeps me human at times… Keep up the great work.

Comment by Tactical Intelligence
2013-08-31 11:44:41

Thanks for the comments Carol! Coffee filters would work great in this filter type.

Comment by Senior Veteran
2013-08-31 06:44:11

Saw a news flash that villagers in Africa lay 2 liter bottles of water in the sun, on the
corrugated metal (roofs), for 8 hours.

The Sun is very powerful, and seems to sterilize the water, it is claimed.

Any comments?

Comment by Tactical Intelligence
2013-08-31 11:43:15

You’re absolutely right. It’s called the SODIS method and it’s very effective (so long as the water is clear). Dirty (sediment-filled) water will not sterilize in this manner.

Comment by Aussiebushman
2013-08-31 08:02:35

To make a far more effective filter you can use alternating or successive layers of the same material that you used plus sand(which makes a big difference), example from the bottom up: cloth, charcoal, cloth, sand, cloth, charcoal, sand, grass and then different sized stones. Also the stones do provide a function by attracting and thereby removing larger particles. By using this method I have reduced the overall particulate size dramatically. Alternately I use a Millbank bag(but with much clearer water).

Comment by Tactical Intelligence
2013-08-31 11:45:17

Thanks for the great tip! I’ll have to try this method out.

Comment by Arthur
2013-08-31 08:37:31

Easy and simple. I like it. ut, how many times could this filter e used before making a new one? Thanks

Comment by Tactical Intelligence
2013-08-31 11:40:45


It’s hard to say. Depending on the water and how much sediment it has will determine how many times this will filter before clogging up.

Comment by Michael Hylton
2013-08-31 10:38:29

Great info and comments too! Thanks for sharing!

Comment by Sergeant Major
2013-08-31 11:17:41

Actually boiling water is unnecessary you can pasteurize water by bringing it to 145 degrees for 6 minutes. This can be done with a solar pond.Google water pasteurization. I use coffee filters from the dollar store to filter particulates. The are lightweight, cheap and take up almost no space.

Comment by Tactical Intelligence
2013-08-31 11:40:06

That’s right. The SODIS method is particularly useful in this situation. Thanks for the comments brother!

Comment by Ken
2013-08-31 12:18:59

For more effective use of the carbon filter element in any filter ‘activated charcoal’ is 50% + more effective. Before you go saying where do you fing that in a survival situation, all that is is charcoal that has been heated up to drive out any moisture. I am assuming that in a survival situation you will most likely be needing to make the charcoal, in which case it would be ready to go. Otherwise you can take the embers you have and put charcoal brickets over them and cover them with earth to exclude O2 or put them in a metal can. Also, a lot slower method, but much better method is to use the bladder of a pig or larger animal to filter it through. While I worked in research we sued pig bladders as a semi-permiable membrane for osmosis and reverse osmosis expiraments. Ther would effectively remove salt from water and it is much smaller than any microbes or viruses. If you can treat them with tannin they will last longer too.

Comment by gayle
2013-08-31 14:22:24

Thanks so much for the video , I always enjoy watching them and learning all I can

Comment by Duncan
2013-08-31 15:14:36

No. Charcoal is only partly combusted and has a very, very high surface area in which it traps bad chemicals and bacteria. Wood ash is (mostly) fully combusted and lacks the high surface area of charcoal. It would likely filter out particulates, but it is full of left over salts that would dissolve in small amounts in the water, making it brackish.

Comment by Anthony
2013-08-31 17:16:24

Good Stuff, Erich

Thanks for taking the time to share this information.

Comment by Greenmoon
2013-09-02 13:37:51

Thanks everyone for the great tips….this is a fabulous site

Comment by Mark
2013-09-03 14:12:57

What is the SODIS method?? Thanks. Great video!!

Comment by Ed
2013-10-08 14:39:53

Thanks for the video. It was well done.
I must have missed the reply about the use of commercially produced charcoal briquette. This would primarily be for us bug ins .

Comment by Tactical Intelligence
2013-10-08 14:56:14

Hey Ed,

It would be best to avoid using commercial charcoal briquettes since many of them have chemicals in them to help with starting the fire. These chemicals will leach into the water turning it poisonous. At minimum just make absolute sure that it is pure charcoal and nothing else.

– Erich

Comment by Sunshine
2013-10-19 19:18:25

Which materials work better for the filter? Most websites claim that coffee filters are more effective. If I use this water filtration device for dirty creek water, will it make it clear, colorless and odorless? How would the world become more effective at preserving the finite amount of freshwater if we all were using these filtration devices?

I think your video was very descriptive and provided productive information on how it works.

Comment by Sunshine
2013-10-19 19:31:43

Which materials are the filter systems?

Comment by Bob
2013-11-01 23:37:01

SODIS method used Ultra Violet rays of sun to kill germs. 2 liter bottles need to be clear.
this site has some more info

Comment by Bob
2013-11-01 23:56:17

Excellent training videos. Thank you!!
Here is a link about a Sand Filter. It can be continuously operated and produces pretty safe water. Takes a while for it to optimize the helpful micro organizes so best for a fixed location, like base camp.

Comment by boliso
2017-02-19 23:40:06

I’d want it a LOT bigger than that. Like an entire pair of pants. The pevlic area full of gravel and moss, the upper leg full of sand and the lower leg full of charcoal, with a lot of layers of cloth at the bottom, to keep AMAP of the charcoal out of my water.

Comment by boliso
2017-02-19 23:42:34

I”d boil it if I had the resources, but I”d be willing to risk drinking it straight from the pantleg, if I lacked those resources. But I do NOT trust just a couple of inches of each of the ingredients to do the necessary cleaning of the water!

2017-05-22 22:59:11

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