Cook onion in butter until tender but not brown. Combine meat and seasonings; beat thoroughly. Beat in flour, then beat in egg. Gradually beat in water. Add onion. Form into 1 inch meatballs and brown lightly. Put cover on pan and shake to turn balls or use a spoon. Pour in tomato sauce and a can of water. Stir to blend and cook on medium heat about 45 minutes. Turn down and simmer the last 15 minutes.