Ok.... so it's day 3 after getting Gizmo. He is still hiding under the bed in my room. He has come out from underneath a few times yesterday. I can pet him and hold in my arms and he purrs away like a baby. He used his litterbox for the first time today and ate only little bit of dry food only today when i put cat nip in it. He refuses to eat any sort of wet canned food. His eyes turn back to blue and then back to red when he is stressed or nervous i have noticed.
Oh, don't worry too much. I am sure he will be fine, really! He just doesn't trust you yet. Try to leave him alone as much as possible, he will decide he needs you and come to you. I had a kitty like that years ago and she turned out to be my bestfriend ever.
What you should do about the hiding under the bed is this: Have all your family members sit in a circle with no space for Gizmo to escape. Let him approach each person, and if he develops feelings for them, he will want to see them even more. DO NOT ALLOW ANY UNFAIR ATTENTION SCHEMES! I got this info out of a book by Sara Hodgsen.
OK I admit, I am a horse person first,dogs second and cats...well I like 'em ok... Siamese cats are very sensitive. Let the poor creature hide and come out on his/her terms. Don't worry about drinking.Cats don't require as much water and I promise, he/she will drink...this cat may be feeding on your anxiety and the more you worry over it and not give it the privacy it needs, the more it will hide and not come out for neccessities! Try going out for a very long shopping trip with dinner and a movie...be gone a LONG time. Sounds like this cat needs some privacy.