Brown ground beef in large saucepan or Dutch oven over medium-high heat until thoroughly cooked, stirring frequently. Drain.
Add water; bring to a boil. Add potato slices; mix well. Boil over medium-high heat for 15 minutes, stirring occasionally.
Stir in milk, sauce mix from packet and onions. Cook an additional 4 to 6 minutes or until mixture is thickened.