Right now the only value to having larger containers is convenience. Excepting the 3l jar, (which somehow compresses water into a smaller volume), everything takes up the same space- except larger containers are heavier.
Plastic bottles are the best containers stat-wise, they're the lightest.
The tradeoff is taking a longer time to collect more than 500ml of water.
I'm not sure how I feel about that.
As for wearable containers, they would only be valuable if they DON'T create encumbrance. They have to be slotless, otherwise they take up valuable encumbrance and gain nothing from their wearability. If they're slotless on the other hand, their volume becomes a non-issue. Presto chango all the cool kids wear waterskins & canteens.
Going off-topic from volume:
Volume vs storability.
Basically, using true volume, (water displacement), as the measure for how much you can stuff in your backpack isn't the best system- it doesn't account for the difference between trying to tuck a baseball bat into the side of one's backpack and trying to stow a pile of bent & chopped up chain link fence; the latter will take up a lot more volume in your backpack despite having a displacement equal to a bat.
The obvious solution to this is 'well give it a value that's truer to storability than displacement'. Fair enough, but now you've got a psuedo-volume that can be misleading.
If that last bit is the case, suggestion: change the term 'volume' to avoid confusion.
If that isn't the case & the 'volume' stat for items is their true displacement: we shouldn't be using that to model storage volume!