TANSTAF1...sorry I misread your post about ON BODY....I'm new to the forums but this is an issue I am concerned with. My original thought was to "dumpster dive" for a bottle and use the Katadyn ClO2 tabs to disinfect...the fold up "platypus"bags are a solution,along with roasting bags, mother's milk storage bags but was looking for something with a smaller profile than the way the cap lays. I wanted a multi use solution is part of my on body carry...the soft stuff..the signal mirror, Bic lighter/button compass, hemostatic gauze, 2x3 gauze, knuckle bandaids, Katadyn tabs, foil roll of Motrin/Tylenol/Aleve tabs, and mosquito wipes ride in the top half (folded)of a 4x8 heavy duty ziploc type bag. Zipped it holds 300ml. Seams are reinforced with, and bag is completely covered with very thin "Duck" brand automotive tape. regards Les