Core apple and chop into small cubes, about 1/2″. (Leave peel on.)
Combine cabbage and apple in crockpot.
Add vinegar, water, and sugar; stir well.
Cover and cook on low for 4 hours.
Notes
I used green cabbage for this dish, which made its presentation a little lackluster. Red cabbage would be a fine (and more colorful) option for the dish.