To build a fairly good waterfilter you need sphagnum moss, peat and charcoal.
In addition you need some sort of container.
Start by making a number of small holes in the bottom of the container.
Also remove the top of the can if that is what you are using.
Place a layer of sphagnum moss in the bottom of the container.
Fill the can app. 2/3 with a mixture of crushed charcoal (not powder, just fine gravel-size) and peat.
Add some more sphagnum moss on top of the peat-charcoal layer.
Place a layer of small pebbles (1/4" or so) on top.
The filter is now ready for use.
Gently pour water on top, collect in bottom.
Let a couple of volumes of water flow thought first before any is collected and used.
Wilderness Survival