how about this as a way to get %99 filtration with a tree branch!!
.. branch filter

"If you've run out of drinking water during a lakeside camping trip, there's a simple solution: Break off a branch from the nearest pine tree, peel away the bark, and slowly pour lake water through the stick. The improvised filter should trap any bacteria, producing fresh, uncontaminated water."

OK, this is fun but pouring water through a stick seems like the hard part. Maybe you could jam it into a funnel and seal it somehow. Plus, there's the violation of LNT.

What they actually did was put the stick into a rubber tube that was sealed with a hose clamp and epoxy to make sure there were no leaks. With a 0.6" diameter stick, a head of 2' to 11' they got flow rates of 4 liters per day. That's not exactly going to put Sawyer out of business for camping gravity filters.

But as a cheap filter element for a device aimed at for developing countries they may be onto something.

And I like that the paper actually has two high school students as authors and one of them comes from my father's old high school. You can read the actual paper and see the diagrams and a sample of filtered water here

Very Interesting subject, using something readily found in nature as a water filter. The article says they tested the filter under 5 P.S.I. pressure. I would think you could reach that pressure easily by raising your water supply up on a tree branch. I'm guessing the higher you raised it the more pressure and more water flow along with a larger branch and larger tube dia. This Is all speculation on my part but I'm guessing the hose clamp and epoxy could be eliminated using the natural taper of the tree branch matched to the tube size and the stretch of the tube material. I'm guessing the epoxy and hose clamp were just to ensure a 100% seal for testing.

Suddenly, in the thread "Stranded? What is your one piece of gear you want?," a sudden influx of 'rubber tubing and hose clamp' replies... :)

Yes, the goal of using the low pressure was so that it could work with gravity feed rather than a pump in a low tech setting. That saves you cost and time and energy for the person using it. All are a big deal in a developing country setting.

You might be able to get away with just using the taper of the branch but one small gap in the seal and your water may be much more dangerous. Of course, in the BW or Q you can also just go out to the middle of the lake to get water and you have a few days to get rescued before you get sick anyway.

I am tempted to play with this at home.

If you take a full container of lake water and set it next to an empty one then twist a paper towel and insert it from the bottom of the full one to the other by the end of the day they will both be half full and your water will have be filtered.

andy..thanks for the link!!..i found that late last night and just skimmed over it.that link cleared up a lot of questions i had.
i think we are putting the filter people out of business,now where did i put that paper towel??!!

So I am not a scientist and you should not take anything I say as proof.

But if I did my research right, they are saying this is good to 70 nano meters. Giardia cysts are 8-14 micrometers and Crytosporidium oocysts are 4-6 micrometers. 1 micrometer = 1000 nanometers. So this would work very well for these cysts.

However, they say it would not work on most viruses, so when the zombie apocalypse happens, we all need a different back up plan...

I need to add plastic tubing and epoxy to my ditch kit.