Preheat oven to 325 degrees. Lay turkey size (19" x 23 1/2") oven bag in 12"x18" baking dish. Place corned beef, water and carrots inside bag. Close bag with twist tie. Make 4 to 5 half inch slits in bag near closure. Bake 2 1/2 to 4 1/2 hours or until tender. When meat is almost done, carefully open bag and add potatoes and cabbage. Reclose bag; cook until vegetables and meat are tender.
MICROWAVE OVEN: Follow directions above, using 12"x18" baking dish. Reduce water to 2 cups. Close bag with rubber band. Micro-cook at high (100% power) for 10 minutes. Reduce power to medium (50% power) and cook 30 minutes. to turn meat, use hot pads; grasp bag at closure, gently lift and bring closure to opposite side of dish. Add potatoes and cabbage to bag; reclose. Continue cooking at medium power for 40 to 50 minutes or until vegetables and meat are tender, rotating dish periodically. Let stand, covered, 10 to 15 minutes before opening bag. To serve, carve corned beef diagonally across the grain in thin slices.