I was there Oct 2008, very dry on Kaliana ridge (no water at all, until the foot of the climb to the Castle saddle where there was a small soak.) Cooyoyo Ck was flowing, a little sluggishly. I was there again this year, Kaliana ridge had water dripping from the Castle, Cooyoyo Ck was *much* more sluggish ... even though the first trip was at the end of the drought, and the second had ample rainfall. You'd want to treat it in either case. After the last trip, I can imagine C.Ck being nearly dry, but in view of its flowing during the drought, I can't imagine it being bone dry. The number of people there, though ... maybe they drank it dry
Along the track from Castle Saddle to MV there are cliffline drips/small bodies of water. At the Northern end of MV (green room?) there's a creek which would have to be perennial. That's quite a way further along. You'd have to get an early start to be able to get there and back to Cooyoyo before nightfall (or be a much faster/lighter walker than me, which is distinctly possible.)
BTW, I wouldn't expect to find firewood around Cooyoyo - it's picked clean ... so best to rely on stoves (as per the mgmt plan.) Also, you'll get to check out the dunny with the best view in the universe.