Heat silverside in a deep frypan over medium-high heat. Cook until browned on all sides. Stir in water, tomato sauce, vinegar, onions, garlic, brown sugar and salt. Bring to a boil then cover and reduce heat to medium-low. Continue simmering until tender, turning beef occasionally, 2 1/2 hours to 3 1/2 hours.
Remove beef and allow to cool before slicing the meat against the grain. Place slices in a 20x30cm baking dish or large platter and pour gravy on top. Cover and refrigerate overnight. Remove any excess fat and reheat before serving.