My travel-sized CPAP doesn’t use a water tank, it uses cartridges coated with a material that absorbs moisture from your exhaled air and gives it to the dry incoming air. A plain old mask helps just because it’s got lots of surface area and it’s inherently slightly cooler than your freshly exhaled breath (which means it will gather at least some condensate from your exhaled breath), but these chemically treated cartridges (especially the “Plus” rated ones) really do great. For my last few flights to/from Japan (12-13 hours each way), I’ve started using this thing whenever I’m not eating/drinking/talking, and it makes a fantastic difference in how I feel during the flight.
I do still drink plenty of water. Getting up to pee during long flights is important:
- It’s a useful sign that you’re well hydrated, and
- getting up to move around, stretch, and get blood flowing all over your body is a good thing.