To dream of a canteen represents planning or preparation for the worst. Having a backup plan to restore comfort or confidence in case a troubling or terrible situation comes up.
To dream of drinking from may represents your attempt to regain composure when a situation has gotten more difficult than you expected. Feeling more pressure than you had hoped for. It may also reflect desperation. Using your last resources to deal a difficulty.
To dream of an empty may reflect a sense of hopelessness or that you’ve tried everything you could without any success. A situation is just too difficult to get through.