With the arid and dry climate we've experienced here in GA, I'm very concerned about the birds. How long would it take for a large bird and small bird to get dehydrated?

I would thing fairly quick if there was a problem with a water dish or bottle, maybe die in about 12 hours. I don't really know since because our weather is so hot I make double sure that my birds are never able to tip out or bath out water dishes.

It depends on the size, the smaller ones less than the bigger ones but just make sure they have plenty of fresh, clean water and watch the droppings. If the birds are getting dehydrated, you will notice a reduction in quantity and a higher concentration of ureates in their poop.

Living in a dry climate myself... I have found that a small fountain in the bird room helps with skin and feather moisture.

To answer your original question: I don't personally believe it would be safe to leave a bird without water at all in such condions.... I would think it would take no more than half a day to deyhydrate. But I'm no vet of course...