1. Place beef, mushrooms and onion in slow cooker.
2. Mix Seasoning and water until blended. Pour over beef and vegetables; toss to coat well. Cover.
3. Cook 8 hours on LOW or 4 hours on HIGH. Stir in sour cream until well blended. Cover. Cook 10 minutes longer on LOW. Serve over cooked egg noodles, if desired.
Slow Cooker Tip: For best results, do not remove cover during cooking.