Transpiration, if one has never tried it, isnt very good at producing a lot of water. First, you need sun almost ALL day. The problem with this is, as the earth moves, shadows do too. Once the bag is in the shade, thats it-all done. A way around this is to place the bag, with vegetation in it, on a hill that will not be cast into shade for the vast majority of the day.
Second, you need to POSITIVELY IDENTIFY the vegetation you need. If you choose poisonous vegetation, you ingest poisonous water.
Third, one bag doesnt produce enough water to live off of. My instruction class (YEARS ago), I believe said that these can produce up to a cup of water, per day. What you need to do is place about a dozen of them out, daily, to make up enough water to live off of. The upside, you simply put them out, and leave them.
AS a water carrying device, I say its outstanding. When I hike, I usually take a large nylon bag for gathering water, and filter from that. You could do the same with that oven bag. As a primary source of harvesting water though-I would say dont bank all your needs on that. In theory, transpiration is great-people just dont realize that one bag doesnt produce much.
Oh yeah, the water from transpiration tastes like the host vegetation-just an FYI