<Doug Ritter of course has very good info elsewhere on this site.

That's on the site home page under sections 'gear and equipment'.
Just thought I'd say where it was in case you didn't know. People keep asking questions of us amateurs on this forum, when the expert has given the facts already.
But it's fun kicking this stuff around isn't it?

http://www.equipped.org/watrfood.htm#WaterPurification

The Sock