Ever since they introduced those rules about liquids/gels/aerosols designed to keep us safe from terrorists with full-sized bottles of deoderant, carrying a bottle of water has been problematic.
You can usually take an empty bottle with you, but last time I flew to Europe, I forgot to empty my bottle in Singapore and had it confiscated when my hand luggage was x-rayed before I got back on the plane (I wonder what they sell in Changi airport that's dangerous, and whether it wouldn't be more effective just not to sell it rather than screen all the passengers who've only been in the secure area before they get back on the plane?)
Then to my horror I found that Air France do not serve bottles of water. They serve CUPS of water. Now this might seem like a good enough idea, until you want to sleep (or in my case, medicate yourself, then sleep) and realise that every time you wake up thirsty and want a mouthful of water (in my case, seems like about every 15 minutes on a plane, where it's dry as dust and you're completely dehydrated) you have to get up and walk to the galley for another glass, which you then have to drink all of because you have no-where to put it while you sleep, which leads to a seemingly endless cycle of short sleep > wake up > drink cup of water > short sleep > need to pee > wake up > pee > drink cup of water > short sleep > need to pee > etc.
They utterly refused to give me a bottle.
Anyway, I have found the solution. One of these, rolled up in your pocket and then if you forget to empty your standard water bottle you've got a back up. I have ordered one - I'll let you know whether it's any good once it arrives. Should also be good for carrying while sight-seeing - it's lighter than a standard bottle.