Can water be freeze-dried in the way that say, coffee can be freeze-dried?
Sure thing. To reconstitute, just add water.
I should bottle it and sell it at an insanely high price.
Just imagine what we could charge for freeze-dried homeopathic remedies!!
In freeze drying, first a substance in frozen so that all the water is in the form of ice crystals. Then the water is sublimated off. This is like evaporation, but entails going from solid to vapor rather then from liquid to vapor. The result is that all the water that was in the substance is gone. What remains can be restored to its original condition (or very nearly so) by adding water back to it.
So if you freeze dry, say, a liter of water, you end up with everything that was in it except for the water. All you have to do to restore it to its original condition is add a liter of water.
Just to pick nits, all you need to add is a liter of pure water; otherwise you’ll end up with a liter of water with roughly twice the normal amount of… stuff… in it.
Unless it was pure water you freeze-dried in the first place!
Doesn’t this one come up every three months or so? 
When I was a kid, the anwer to this was “Just add milk!” on the silly premise that powdered milk was re-constituted by adding water, and that the reverse could be done.
I bought some powdered water, but I don’t know what to add to it.
– Steven Wright
I remember reading this in a Gyro Gearloose comic. He’d invented two powders which, when mixed, produced gallons upon gallons of water. He was very successful selling these powders during a town water shortage, until the citizens realized that the reason there was a shortage was because Gyro was consuming immense amounts of water in his lab to produce the powders.
Isn’t the the same mechanism that causes freezer burn?
Oooh! This question makes me dizzy, and kills puppies too.
Cute puppies!
You can get that at the same place you get lefthanded stovepipe wrenches and rolls of shoreline.
Yes. The commercial process uses much more expensive equipment and is much quicker, but the basic physics are the same.