Dark blood flowing continuously means a vein has been damaged. Bleeding is stopped with a tight dressing, and raising the arm reduces the blood flow. Water would wash away the blood clots, and iodine would burn the tissues and not stop the bleeding.
Dark blood flowing continuously indicates venous bleeding. The most effective way to stop this type of bleeding is to raise the injured limb (to reduce the blood flow) and immediately put a tight dressing on the wound.
Option 1. Washing a bleeding wound with water will remove the forming blood clots and increase the bleeding.
Option 3. Pouring iodine straight into a deep wound burns the tissues and does not stop the bleeding.