Crockpot Corned Beef and Cabbage

1 (4 1/2 pound) corned beef brisket
2 medium onions, quartered
1/2 teaspoon pepper
3 tablespoons vinegar
3 tablespoons granulated sugar
Potatoes (optional)
Carrots (optional)
1 cabbage head, cut into small wedges
2 cups water

Combine ingredients in crock pot with the cabbage on top. Cut meat to fit, if necessary. Cover and cook on LOW for 10-12 hours or on HIGH for 6 to 7 hours.