Uncover remaining icing, and add any icing from piping outlines into bowl; mix well. Stir in warm water, 1 teaspoon at a time, until icing is consistency of heavy cream. (Make sure icing is mixed well before adding next teaspoon of water so as not to add too much.) Pour thinned icing into squeeze bottle; screw on top. Keep squeeze bottle tip and any remaining icing covered with plastic wrap to prevent drying out while decorating.