Bottle of water (or any other liquid)

[Ongka]

You'll probably have to edit the lantern model located in "redist\models\hand_objects", but that would destroy your lantern.
I'm not sure if you can create additional hand_objects, as there is a pickaxe folder located in there.
Even if it would be possible somehow, it's way too complicated to implement for just a little extra effect.

You might just change the laudanum image to a water bottle, but that would require you to do a full conversion.