I like survival and here is the simplest water filter that might help you out of a tight spot. Skipping the intro, this is going to show you how to make a completely Recycled Simple Water Filter.

Supplies

You're only going to need a:

1. One Liter Water Bottle

2. A knife

3. A source of rocks

4. A source of charcoal

Step 1: Cutting the Bottle

All you're going to do is cut the back of the bottle off. This will allow an opening and the start to building a filter.

Step 2: The Cap

You need to make holes in the cap, not too big or the insides of the filter will fall through. you can make these holes by any means necessary. With a knife or any other sort of sharp object. I personally used a drill for convince. Make sure you screw the cap back on tight when fished making the holes.

Step 3: Charcoal

Charcoal is found usually after a fire ends. It is a logs black remains. You need to find or make some, and crush it.

Step 4: Resources

You're going to need small rocks the size of a finger nail and make another pile of rocks, larger than the previous rocks.

Step 5: Construction

You're going to pack in the charcoal, then place in the smallest stones and work your way up in the stone size. Once you complete this its done and your water filter is ready.

WARNING: THE WATER WILL COME OUT BLACK AT FIRST, WAIT UNTIL IT BECOMES CLEAR. THEN IT IS OKAY TO DRINK.