I think the problem is that:
1) there's only 4 units of drink in the skin. So it will be emptied on first drink.
2) the skin is named in the wrong order. If you look at all other drink containers, you'll see that they have the named of the liquid as the last alias:
Code:
#3000
barrel beer~
a barrel~
A beer barrel has been left here.~
#3001
bottle beer~
a bottle~
A beer bottle has been left here.~
#3002
bottle dark ale~
a bottle~
A dark bottle of ale has been left here.~
#3003
bottle firebreather~
a bottle~
A bottle of firebreather has been left here.~
#3035
fountain water~
the large fountain~
A large fountain carved from blue-streaked marble is here, bubbling merrily.~
If you change the alias to "waterskin skin water" instead, it'll probably work.
