there is disclosed a hydration bag for providing potable or even sterile water from contaminated water sources . specifically , there is disclosed two embodiments of a passive membrane osmotic device . the first embodiment has an interior space sealed with one or two membrane walls , having an osmotic agent formulation within the interior space , and having direct osmotic concentration properties . the second embodiment has a sealable nutrient / osmotic agent chamber with a spiral wound membrane wrapped around the nutrient / osmotic agent chamber to form the membrane element , wherein the membrane element is located within a sealable dirty water compartment or within a dirty water source and wherein the membrane element communicates with a clean water compartment . more specifically , the osmotic agent or nutrient can be a partially dehydrated food source , a sugar , a medicine , or combinations thereof .