Container size definitely seems to be a factor.
If I had to guess, I’d say that the game makes you take longer to defrost larger volumes (sure, great), but then it applies the external cold to your container for that same duration, and the whole thing re-freezes before you can take a sip.
Water currently freezes REALLY FAST in cataclysm. Slowing down the rates of freezing considerably might help a lot. Water itself has an incredibly high thermal conductivity, but the containers we usually store it in - and the air - do not, so significant volumes of water should not freeze in a matter of minutes unless it is insanely cold out, and personal body heat would be enough to counteract most freezing for containers carried/worn near the body.
It would of course be nice to see a new category of liquid storage - insulated canteens/thermoses that greatly slow the rate of background temperature change for their contents, at the cost of a bit of additional bulk.
