The slow cooker is the perfect way to go for this traditional dish, since it must bubble away untended for hours, in any event. Be sure to serve with crusty bread, and Dijon mustard and horseradish on the side.
In a 6-quart electric slow cooker, combine the water, vinegar, sugar, pepper and onions, mixing well. Place the corned beef in the mixture. Scatter the potatoes over the top and along the sides.
Cover and cook on the High heat setting 4 hours. Remove the lid and scatter the cabbage wedges over the top. Cover and continue cooking on High 3 to 4 hours longer, or until the beef is tender. To serve, carve the beef into slices and serve with the cabbage and potatoes, with some of the cooking liquid spooned on top of the beef to keep it moist. Makes 6 to 8 servings.