Place the onion, potatoes and carrots in a 5 to 7 quart slow cooker
In a small bowl combine the water, garlic, bay leaf, sugar, vinegar, pepper and the contents of the spice packet that came with your corned beef and pour over the vegetables.
Top the vegetables with the corned beef brisket and then the cabbage.
Cover and cook on LOW for 8 to 9 hours or until the meat and vegetables are tender.