Combine water, vinegar, sugar and pepper, in the bottom of a 6 quart slow cooker. Mix well.
Then place the onion into the water mixture. Add bay leaf.
Place the rinsed brisket on top of the onions, sprinkle with seasoning packet.
Scatter the potatoes and carrots over the top and along the sides of the brisket.
Cover and turn pot to high. Cook for 4 hours.