1.
Set potatoes, carrots, and onions in a large slow cooker. Top with beef. In a separate bowl, whisk water together with Italian dressing and pepper, then drizzle over beef.
2.
Cook on Low for 8 hours.
3.
Transfer brisket and vegetables to a plate and cover with foil. Pour cooking juices into a saucepan and set over high heat.
4.
Whisk cornstarch together with cold water in a separate bowl. When cooking juices reach a boil, add the cornstarch mixture and boil for 2 minutes to thicken.
5.
Serve corned beef and vegetables with sauce spooned over each helping.