I appreciate your comments. And, I would add....Filters don't filter out Viruses, they can't by definition. And, tablets or Iodine take a long time (hours) to work if the water is cold, as it always is here in the northwest. This is a fairly complex subject. Colin Fletcher and Chip Rawlins do a good job of explaining it in The Complete Walker IV (pages 237 to 252).
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Jim M