Don't give him any more water! The best thing you can do is put him back in his nest if you know where it is, though it doesn't sound like you do. I'd take him to a vet or an animal rescue center if possible. He may have other injuries you can't see and he needs to be checked over. The vet can also direct you best what to feed him. You should be able to find a baby bird formula at a pet store. You can feed it to him with with a syringe. I wouldn't give him anymore apple or walnut or anything else until checking with someone first. Baby birds need to be fed VERY often, so it is important you get him baby bird formula as soon as possible. Or get him to a vet or rescue center.