I know a lady who put down dry dog food and her dog wouldn't eat it. The dog drank water for three days and then realized...this is it. The dog ate the food. If they are hungry enough..they'll eat. A dog will not let themselves starve to death. They will even eat grass if they are hungry enough. It is instinctive behavior. It is the humans that crumble into the dog's will.
If your dog is not eating and only drinking make sure nothing is stuck in your dog's teeth. My dog would do the same and he had something stuck in his teeth.
My chihuahua, gizmo is EXTREMELY picky. He won't eat unless I mix some human food into his food. Meat leftovers and shredded cheese is what I usually use.