I was on the bepreparedtosurvive.com and saw a survival water system they offer (http://bepreparedtosurvive.com/The%20Aqua-Pouch%20Plus%20Water%20Purification%20Kit.htm). They made a pre-filter from heat-bonded plastic to hold a #4 Melita water filter. I have a Seal-A-Meal and I thought I would try knocking one off.
I traced out a #4 filter, heat sealed the diagonals, punched a row of holes in the bottom with a paper punch and trimmed to suit. 4.7 grams!
Works best with containers with a large opening, but you can scrunch it into a Nalgene. It is fine once you get a little water and weight to settle it down. I made another to fit #2 filters.



