Put beef in a slow cooker.
Whisk water, gravy mix, and stew seasoning mix together in a bowl until no dry mix remains; add Worcestershire sauce and pour over the beef. Add tomatoes, carrots, potatoes, celery, and onion.
Cook on High for 6 hours.
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.
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