Over the years I got a small collection of Lotusphere water bottles. It started in 2003 when I ended up with a couple of extra bottles in my backpack on the last day, and I brought them home with me. The next year I picked up a couple again to drink at the airport while waiting for my flight, and I got one leftover as well. Since then I made sure I bring home at least one bottle per year for my little collection.
This year I noticed that the older bottles were squished, like there were vacum inside. The older they were the more squished. I let some air in and noticed that it seems like water is evaporating despite the bottles being closed. Quite interesting, since there was a vacum inside. It seems like the water evaporates and get out, while air is not able to get in. The bottles have been stored above the washer, with the dryer a few feet away. Might be the temperature that did it.