If you ever find yourself in a survival situation for any length or time, you’re going to eventually have to find water. Unfortunately, most of the water sources you encounter will have the potential to be polluted, murky and crawling with bacteria. Sure you can boil the water you find in the wild to kill germs, but boiling water will do little to remove particulate matter like sand, mud, clay, silt and rotting vegetation. That’s why you have to filter it first before boiling it, or treating it with halizone tablets or other sanitizers.
Other than a piece of fabric from a piece of clothing, we often don’t have efficient filtering media in our possession in a survival situation, but you may be surprised to find it all around you. You just have to know where to look.
The filter media
Ideally you want to collect clean gravel, clean sand, charcoal, long green-grasses, and that piece of fabric I mentioned earlier. The best way to find clean gravel and sand is to scoop the top layer that has been exposed to the sun and either toss it up to let the wind separate the dust or rinse it in your dirty water. You have to sanitize your filtered water anyway. You get your charcoal from the bed of a fire and you want to find some way to rinse or blow off the charcoal dust the same way. The fabric can come from a piece of your undershirt or the tail of your shirt.
A 2-liter plastic bottle is shown as an example, but you can use an empty, plastic milk bottle or other plastic bottle as long as it can hold a good amount of your filter media and water.
First, you have to cut off the bottom or the base of the plastic bottle. Eventually you’re going to carefully pour your various filter media into the bottle in layers.
Layering in the media
You want the size and porosity of your media to decrease as the water filters down, but you also have to filter the media such as sand. Sand in water is crunchy on the teeth the same was as sand in a sandwich at the beach.
- To start the layering, tie the fabric around the spout of the bottle. This will be the final filter before the water drips into a container or pot.
- Next, crumple up and fold over a large piece of fabric as your first layer at the bottom.
- Top the fabric with a 1-inch layer of criss-crossed, green grass.
- Top the grass with a layer of charcoal about 1-inch thick.
- Top the charcoal layer with a layer of sand about 2-inches thick.
- Top the sand with a layer of gravel about 1-inch thick.
I think you get the idea. You’re trying to use various layers of material or media of various sizes to filter out any rotted vegetable matter and particulate matter. As the dirty water percolates towards the bottom particles of smaller and smaller sizes are filtered. The charcoal will help remove any odors present in the water.
There are substitutes for the filter media you can consider as well. If you happen to be in a location without grasses you can use green leaves or pine needles in a layer. You can also substitute sand with more gravel. The charcoal is also optional but it sure helps to get rid of any strange flavors especially in tannic water stained by rotting, brown leaves and bark. The fabric is fairly critical for smaller particles. If you have to substitute and the water is still off-color you can always let it sit after boiling or chemically treating it, and allow the particles to settle to the bottom. Just be careful to skim the water off the top of the pot so you don’t stir up the stuff at the bottom.
However! You’re water is not yet safe to drink. Microscopic bacteria may have survived the filtration trip and you need to dispatch them. Boiling is safest. Boil your water for at least 10 minutes with a gentle boil. Cover the pot if you can so you don’t lose too much water to evaporation. You can also add halizone tablets to the clear water and let them soak for 15 minutes. Don’t forget to stir the halizone-water with a stick or your finger to distribute it. Failing that, you can add 1/4 teaspoon of bleach to one gallon or water, or 20 drops of iodine to one gallon of water. Some folks recommend that you add the bleach or iodine to the water before you filter it so the charcoal can remove any after taste of iodine or bleach. The problem with that approach is the fact that you have no guarantee that your filter media is biologically pure, although that approach might sanitize at least some parts of the layers as well. Personally, I prefer the boiling approach but that assumes you have a pot for boiling the water. It’s never easy, but if you take the time you can get to clean, clear water safely.