I like the Katadyn and MSR filters. They are fairly light and easy to use to filter large amounts of water quickly. I carry purification (putrification?) tabs as back up. However, I never forget that boiling is the easiest and best way to purify water, and is doable anytime, anywhere without any other equipment but a can to hold the water. I often boil water just for the practice, and it gives me something to do while sitting by the fire.
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"Most men take the straight and narrow. A few take the road less traveled. I chose to cut through the woods." ~Unknown~