After filling the Christmas tree stand's reservoir with water on Monday -- somewhat in a panic, I'm ashamed to admit -- I'm happy to report the tree is doing very well. The water level has receded only slightly. I can't be sure if the tree has soaked up the small amount of water, if it has evaporated from the stand, or if the dog has helped herself to it. But it's a negligible amount, so it doesn't really factor into our experiment.
Based upon experience from prior years, I'm comfortably certain that if I hadn't added the Vacation preservative to the reservoir water on day 1, the tree would be drinking up a standful of water every day.
Follow the experiment, day by day, and stay tuned.