Rating: 4 / 5
Ray's filter system design intriqued me. As with the iodine treatment Polar Pure, there is no shelf life to this system. Like Roy, I followed the instructions found in Beyond Backpacking. However my filter is a little thing called the Survival Straw. The Survival Straw is intended to work by sticking one end in a water source and sucking on the straw end. So I stuck the water source end of the Survival Straw filter through a hole in the center of the fabric circle. I secured the fabric around the plastic filter housing with rubber bands. Surgical tubing replaces the removeable straw.
My first version is made from 30" dia siynylon circle, 6' surgical tubing, 1/2" nylon webbing loops and weighs 4.12 oz. Since I have .7 oz spinnaker fabric now, I will re-make the bag portion with lighter fabric, debulk the bag by sewing the bag in a cone shape and sealing the seam with silicone, and using grosgrain for loops.
For added filtration, a large coffee filter or two can line the inside of the fabric bag to trap large particles. A folded up white kerchief is another simple prefilter. (White makes it is easier to see the crap that is being strained out of the water.)
The tubing can taken off and used to siphon water out of small pools and into the filter bag. It can also be used as a sling-shot.
The effectiveness of filtration on truely cleaning water is a bit of a gamble. I just came across a study in Helsinki that indicated that reverse osmosis cartridges were the best at getting rid of all the big baddies, pp 33, 41. Another notable survival gear reviewer, Doug Ritter, also has some well reasoned views on water treatment - among other things. I never wanted to spend anymore than the $25 for my filter with all of the EPA re-reviewing going on.
Chemical methods seem to be the cheapest, lightest, and most effective though. For now I will stick with Polar Pure because of the shelf life and ease of use. No iodine taste either (although a little ascorbic acid - vit C - or sugar would nix the taste.) But I really like the simple Ray-Way bag design for collecting water to at least prefilter. In fact one of the filter manufacturers is now including a gravity feed bag in their set up. This design could even be improvised in the field if needed.