Agreed! just like humans an animal can go a fair time without 'food' but will die pretty sharpish if it is losing fluids by vomit/urinating/defecation. Water is essential.
I know nothing about staffies but if you are talking old dogs there are a multitude of reasons for it throwing up; vets is the best place to go. However, ask yourself a couple of simple questions... what has it eaten drunk or lately (anything out of the ordinary? bones/barf/refuse) and where has it been that is either unusual or uncommon (contact with poisons or allergies).