Slow Cooker Pork Tenderloin

lbs pork tenderloin 1 teaspoon ground sage ½ teaspoon salt ¼ teaspoon ground black pepper 1 garlic clove (crushed) ½ cup water ½ cup brown sugar 1 tablespoon cornstarch ¼ cup balsamic vinegar ½ cup water  2 tablespoons soy sauce