If an emergency water filter was needed to be made, does anyone know how to construct one out of natural materials? I have heard you can use hollowed out logs and black ashes with other techniques to make a tube water can be filtered through, what effectiveness could be achieved and does this kind of thing work on salt water?
Actually, water filters are pretty easy, depending on what you want to 'Filter' out...
Salts are not 'Dissolved' and can be filtered out with a 'Membrain' type water filter.
You can also distill the water away from the salts and minerals, (and heavy metals, ect.) fairly easily.
See 'Solar Stills'...
FRESHWATER FILTERING.
You could use anything from layers of 'T' Shirt with fine sand in-between the layers, to sediment settling containers...
First off, let's ASSUME, you have muddy water out of a stream.
The first thing to do is find a container to let the water set in COVERED, so the sediments settle out without insect larva being laid in the water.
Once you have CLEAR water (or if you start with CLEAR water), you can move to filtering.
Although some say a 'T' shirt is enough, it's not.
The weave simply isn't tight enough to catch the 'Nasties' that can be in the water, including Eggs/Larva, Cysts, Bacteria and Viruses.
The most common type of filter is a SAND FILTER.
Dry fine sand over a fire, heat it to the point nothing can live (around 250 degrees F.).
Put that sand, several inches deep, on top of that 'T' shirt and TRICKLE your "RAW" water on top, catching the water that runs through.
This will remove about 95% of the pathogens in the water.
I would further boil it if possible before consuming.