Place brisket in a 10x15 inch roasting pan. Add the crushed ginger snaps around the brisket. In a separate small bowl, combine the onion soup mix with the water. Mix well and pour over the brisket. Then pour the chili sauce over the brisket.
Bake at 350 degrees F (175 degrees C) for 1 hour. Add the carrots, potatoes and onion to the roasting pan around the brisket.
Bake at 350 degrees F (175 degrees C) for 1 more hour, adding water as needed when done to thin the sauce in the bottom of the pan.