1) Chop onion into large chunks and place into bottom of slow cooker. Top with corned beef and seasoning packet that comes with corned beef.
2) Pour water into slow cooker until it covers the corned beef. Add garlic and bay leaves.
3) Cook on low for 9 hours. 
4) After first 2 hours, add potatoes and carrots.
5) After 7 hours, add cabbage.
6) After 9 hours, remove corned beef and slice.
7) Serve with cabbage, potatoes, and cabbage.