How to Make a Survival Water Filter

Updated on December 7, 2018

Basics of a Survival Water Filter

Various types of portable water filters can be bought from the camping and kitchen sections of almost any department or sporting goods store. As a matter of fact, I own a few and I'm not going to lie. I love them. They are nice to have and easy to use. But they also need to be replaced after they have been used to filter out so much liquid. If you actually find yourself in a survival situation you probably aren't going to be able to go down to the camping section to purchase a replacement filter.

I'm about to teach you how to teach you how to make a filter that anybody can make, using materials that are free and easy to find almost everywhere. This filter is going to have four parts all together, but you only need to have these two components to make an effective filter:

  • A housing of some sort. We are using plastic bottles because they are easy to clean, and made of food grade materials.
  • Porous materials to put into the housing. These materials filter foreign bodies out of the water and make it safer to drink.

Start with a Clean Plastic Bottle

Start with a plastic bottle that hasn't housed any pesticides, herbicides, or harmful chemicals. It doesn't matter what size of bottle that you use, or what type of plastic it's made out of as long as you are able to safely cut off the bottom with a pair of scissors or a knife, and drill or bore a hole in the cap.

Try to also start with a bottle that hasn't been out in the sun very much. The U.V. rays of the sun degrade some plastics and make them brittle. Picking out a bottle that has been left in the sun could make this project almost impossible. It would keep splitting, and cracking on you while you were trying to cut it. If you're using larger bottles like the five-gallon water cooler bottles, it could even be dangerous. Using a bottle that has been left in the sun for a long time is just best to avoid.

Now that all of that is out of the way, let's get started.

  • Clean your bottle with hot, soapy water and rinse it out well.
  • Cut the bottom off of the bottle with a pair of scissors or a knife.
  • Lay the cap down on a flat surface and carefully bore a hole in it with a knife.

Choosing the Right Charcoal

Charcoal is going to be the bottom layer of your filter. It's also the most important layer because it's very porous and the carbon in it is going to grab on to a lot of materials that our other two ingredients will not.

DO NOT use charcoal that has lighter fluid in it if you choose to use bagged charcoal. Also, try to use lump charcoal over briquettes if your charcoal is coming out of a bag. It's really best to make your own though or pick some bits of charred wood out of your fire for this step.

  • Put the cap back on your bottle and gather enough charcoal to fill it about 1/3 of the way up.
  • Grind or crush about half of the charcoal.
  • Drop the charcoal into the bottle. Start with the stuff that you ground up and end with the chunky stuff.
  • Tamp it all down in there tightly with a stick. Try to leave as few air gaps as possible.

Gathering and Sanitizing Sand

Though a single grain of sand isn't very porous, a layer of sand will act as a good primer for your charcoal. It will remove larger particles of debris, leaving the charcoal to filter out the finer contaminants.

If you can afford a little bit of time and want to take an extra safety precaution here, sterilize your sand. Spread it on a flat rock or dump it in a metal container, and put it over or beside the fire until it is dry. This will kill off any bacteria or parasites that might be living in it. Just cool it down before you dump it into the bottle.

  • Dump a layer of sand on top of the charcoal in the bottle. Ideally, the layer should be about half as deep as the charcoal.
  • Tamp it down tightly with a stick. It doesn't matter if your layer of sand and your charcoal mix a little bit. The last step will separate them back out.

Gathering Stones and Pebbles

The types of stones that you use doesn't matter all that much, but where they come from does. Try to collect your stones from a riverbed or off the side of a path. Try not to use gravel from roads, or other areas where there are signs of heavy traffic because they are more likely to be contaminated than other areas.

This is the next to last step in the construction of our filter:

  • Collect enough small stones, gravel, and pebbles to make a layer on top of the sand. It should be a layer about equal to the sand in thickness.
  • Tamp the stones down with a stick to try to minimize air gaps.

Priming Your Filter

Testing your filter is your last step. This also will help any displaced elements in the filter settle back into place.

  • Pour water through your filter until it comes out of the hole in the cap clear. It will start off black and then it will lighten and lighten as you put more water through it.

Use Your Better Judgement

Even after the water passes through the filter you are going to want to treat it by boiling it or with chlorine or tablets. Especially if it came from a stagnant source that could easily have been contaminated. If it came from a river or stream of moving water then your chances of still getting sick are lessened. Just try to use your better judgment and take all factors and risks into consideration before you drink it.


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