Update: since this has been linked now I'll edit it to be tidier and a little less blatant about the syndrome name. It might appear as a blank anyway, as the vampire syndrome appears as a blank in the arena, but I can't do anything about that. New dwarven entry text:
Has been tested a little more thoroughly in Arena mode now and seems to work, but even with normal dwarves hunger and thirst work strangely in the arena.
Original text follows.
Edit dwarven blood to be
[SYN_NAME:has bitten a dwarf]
The syndrome name line can be deleted entirely, it's just there so you can keep track of it for testing. To check this out for yourself you need two dwarves in the arena, both on the same side and one of them a vampire. Become the vampire and suck the other dwarf's blood. You should have two syndromes active, one blank one for the vampirism and one 'has bitten a dwarf' syndrome (you'll need to return to the arena to see these). Then go for a swim to kill time. Lie down and sneak as well to pass more time between turns. It'll take about a full day for the thirst status to show. Only the thirst status will show, no drowsiness or hunger.
Thanks to Di for pointing out
that NO_DRINK is a removable tag. I really hope this translates into fortress mode.