[[quoteright:330:[[Film/BackToTheFuturePartII http://static.tvtropes.org/pmwiki/pub/images/pizza_bttf_2.jpg]]]]

Dehydration is a wonderful thing in fiction! It can make anything from creatures to base elements shrink to a easily portable size, and all you need to do to return it to the way it was before is to put a drop of water on it!

Perhaps writers used to have a lot of those expansive sponges or they're very familiar with the factoid that a person is 70% water (a house is seventy percent bricks but try throwing some bricks at some concrete, metal poles and some roofing tiles). However the origin seems to be connected to FoodPills and the idea of astronaut food. Sailors, soldiers and astronauts have needed easily transportable, highly nutritious and long lasting ways of cooking and storing food (and in the case of astronauts, something you can eat in zero gravity), when trying to think of what might be useful for life [[AC:In Space!]], something like this trope turns up.

In a way it's connected to the tendency in sci-fi for large, complex objects to [[ImpossiblyCompactFolding fold or retract into small ones]], such as [[WesternAnimation/TheJetsons George Jetson's]] car turning into a suitcase, those vanishing animal-head masks in ''Series/StargateSG1'', or the capsule items in ''{{Dragonball}}''. In all of these cases, the shrunken item is easily carried, implying all that mass actually went somewhere else. At the very least, there's an overarching trope here- the idea that if you make an object smaller, it magically [[HollywoodDensity gets lighter too]].

There is an element of TruthInTelevision to this trope, at least as far as foodstuffs with a high water content go, as water actually is quite dense. A 1m x 1m x 1m cube of water weighs in at a metric tonne[[note]]Allowing for some variation based on the water's temperature[[/note]] so if you can remove the water from a foodstuff you can remove a significant chunk of its mass. The reconstituted product you get from adding the water back is rarely remotely as palatable as the pre-dehydration product was (though some fruits make quite enjoyable snacks as dried fruit).



* The famous later series of Smash instant potato ads are on a related theme with robotic aliens mocking backwards humans for making mashed potato the normal way when they could just use Smash which is essentially the closest humanity gets to this trope- powder to which you add water to make mash potatoes.

[[folder:Anime & Manga]]
* In the film adaptation of ''Anime/{{Blame}}'', Killy is invited into a settlement that is running out of food. He hands over some rations; 1 king-sized candy bar + 20 gallons of water = 8 cubic feet of spongy "food".
* In the manga-only final story arc of ''Manga/RanmaOneHalf'' Akane grabs hold of a magical heat-producing staff which instantly boils all of the water out of her body, but rather than turning her into a desiccated mummy it turns her into a 6 inch tall doll. To bring her back to life (and normal size) Ranma has to soak the doll in some magical water.

* Employed in one of Carl Hurley's routines involving him going on a dehydrated food diet and losing three pounds... and then gaining five when it rained.

[[folder:Comic Books]]
* The Bash Street Kids of ''ComicBook/TheBeano'' tried making food from dehydrated mash, sausages and gravy once. It went wrong when they used far too much water and the food was bursting out of the kitchen.

[[folder:Comic Strips]]
* ''ComicStrip/SpeedBump'' featured a strip with "Powdered Water: Just Add Water".

[[folder:Films -- Animation]]
* WesternAnimation/{{Megamind}}'s dehydration ray, which is impossibly harmless. If you get hit with it, you get turned into a small perfect cube (presumably equivalent to the mass of you that isn't water, although we never see what happens to the water), and then as soon as that cube gets slightly damp it transforms back into a perfect healthy human being.
** And he uses it on ''everything''. Stray cats, bags of garbage, Minion, ''[[spoiler: himself]]''...

[[folder:Films -- Live-Action]]
* The dehydrated pizza in ''Film/BackToTheFuturePartII''. We laugh when they say "Aw, grandma! Who's going to eat all that?" but then they add the water and you see this massive pizza.
** They also appear in the ''WesternAnimation/BackToTheFuture'' animated series, where Verne would would be bullied for lunch money, admit that he only had the pills, which the bullies then knocked out of his hand and when they hit the wet ground they popped into a full turkey dinner.
* The instant food in ''Film/TheFifthElement'', which has to be parodying this trope - Leeloo grabs what looks like a pepper shaker, off-screen something small is heard rolling into the bowl, and after a few seconds in a microwave, it has become an entire roast chicken with vegetables.
* The 60's ''Film/BatmanTheMovie'' where all the diplomats got dehydrated. Each of them was reduced to a test tube of powder, which didn't appear to be abnormally heavy. They just added water to the powder to return them to normal (Unless you used heavy water... then the results were not so good...)
** The 60's Batman series also featured "instant costume capsules" in one episode. Drop the capsule into a cup of hot water, and it expands into a full sized Bat suit.
* ''Film/SpyKids'' had packets that expanded into Big Macs in a split second after being placed in a microwave-like "rehydrator".
* ''Film/TheForceAwakens'' has ration packets that contain a powdery substance. Drop the powder in a bowl, add a little water, and in seconds it becomes a big, round, muffin-thing.
* A DeletedScene from ''Film/TheBlackHole'' has the following dialogue:
-->'''Lt. Pizer:''' I'm starving. What's on the menu for Christmas Eve?\\
'''[[TinCanRobot V.I.N.CENT.:]]''' Dehydrated turkey, with dehydrated oyster stuffing. Also dehydrated cranberry sauce, dehydrated gravy and giblets, dehydrated sweet potatoes in dehydrated orange sauce, dehydrated vegetable salad, dehydrated mince pie, dehydrated--\\
'''Lt. Pizer:''' ''[firmly cutting him off]'' I envy you, V.I.N.CENT.\\
'''V.I.N.CENT.:''' [[SnarkyNonHumanSidekick That's not surprising]]. Why?\\
'''Lt. Pizer:''' Because you don't have any taste buds.

* In Creator/RobertAHeinlein's short story ''Literature/MagicInc.'', based in a {{Magitek}} AlternateHistory, someone comes up with the idea of using magic to make a tiny raincoat you can keep in a pen sided holder that grows to full size when it gets wet. The protagonist realizes that you could create a huge industry of all kinds of camping supplies or just anything that you want to carry small that you can just add water to make it full sized.
* In ''Literature/EdenGreen'' and sequel ''Literature/NewNight'', humans infected with an alien needle symbiote are able to regrow entire parts of their bodies after disastrous injuries, a process that uses mostly water as raw material.

[[folder:Live-Action TV]]
* ''Series/StarTrekTheOriginalSeries'':
** An alien race from the Andromeda galaxy (the Kelvans) has the ability to "distill" people by using a device on their belts, reducing them down to a porous, softball-sized cuboctahedron. (Water not needed for restoration.)
** Subverted in another episode, when an entire starship crew (except her captain) is dehydrated and crystallized by an unknown pathogen on a planet they visited. The process is shown to be very painful and irreversibly fatal.
* In the episode of ''Series/KenanAndKel'' set in the year 3000, the characters buy all of their food in tablet form. When they add water to the tablets, they turn into the actual food.

[[folder:Tabletop Games]]
* ''TabletopGame/DungeonsAndDragons''. ''Magazine/DragonMagazine'' #73 had the Pill of Plentiful Water. Just add a tiny amount of water to it and it would expand and become a gallon of water.
* Creator/{{Chaosium}}'s ''TabletopGame/{{Stormbringer}}'' supplement ''Stormbringer Companion''. When placed in water, a waterhorse wafer will swell up and become a full sized waterhorse (a demon from the Plane of Probability.

[[folder:Video Games]]
* The original ''VideoGame/SpaceQuest'' game from Sierra On-Line, featured a canister of dehydrated water (hydrogen gas). Part of the game takes place on a desert planet; you actually have to drink the water to avoid dying. You could also throw the canister at the creature Orat. His belly would swell up and he would explode.

[[folder:Web Original]]
* ''Wiki/SCPFoundation'', [[http://www.scp-wiki.net/scp-1122 SCP-1122 ("The House of Tomorrow")]]. The house's kitchen has FoodPills that change into three-course meals when water is added to them.

[[folder:Western Animation]]
* Played straight in an episode of ''WesternAnimation/WhatsNewScoobyDoo'' where melons and other foods are dehydrated to tiny sized, and spring back to normal in a pool.
* Subverted and mocked in ''WesternAnimation/TheSimpsons'' [[Recap/TheSimpsonsS7E4BartSellsHisSoul Bart sells his soul]] for five dollars to Millhouse. He uses those five dollar to buy dinosaur shaped sponges which the page advertises as growing gigantic when made wet. Bart imagines them growing into large dinosaur sized sponges which then frighten Lisa. What he gets is a pair of sponges that get slightly bigger and then get washed by the hose down the sewer drain.
* An episode of ''WesternAnimation/ChipNDaleRescueRangers'' has Monterey Jack unwittingly swallow a piece of "dehydrated cheese" while aboard a space shuttle. It immediately inflates to full size, comically turning Monty into a large brick shape.
* In ''WesternAnimation/FamilyGuy'', when Peter eats a huge amount of dehydrated meals, he initially comments that he's still hungry. Then he takes a drink of water and nearly explodes. (FridgeLogic- wouldn't the meals have reacted to his saliva and other bodily fluids?)
** RuleOfFunny, I suppose.
* In ''WesternAnimation/RenAndStimpy'' Ren ingests a pill labelled "Cowboy's Delight Dinner". It rehydrates inside him as a whole horse.
--->'''Mr. Horse:''' No sir, I don't like it.
** The episode "House of Next Tuesday" features a dehydrated bed. Then Stimpy pees on it...
* In one [[WesternAnimation/WileECoyoteAndTheRoadRunner Roadrunner]] cartoon, Wile E. Coyote uses Acme Dehydrated Boulders. He adds water to one and it expands in his hand - and crushes him.
* An episode of ''WesternAnimation/SecretSquirrel'' had him defeat the [[Literature/LittleRedRidingHood Big Bad Wolf]] by trapping him in a dehydrated grandma's house (which [[AmusingInjuries shrunk when the sun dried it out again]]).
* The ''WesternAnimation/LooneyTunes'' short "Hare-way to the Stars", where Marvin deploys Instant Martians from a gumball dispenser. Bugs later takes it with him to Earth and it accidentally falls down a sewer.
-->Run for the hills, folks, or you'll be up to your armpits in Martians!
* Another ''WesternAnimation/LooneyTunes'' short: "Scrambled Aches," with Wile E. Coyote carrying a box of dehydrated boulders to the edge of a cliff. One drop of [=H2O=] from an eye-dropper, lift boulder high above head, and HilarityEnsues.
* In another ''WesternAnimation/LooneyTunes'' short "I Gopher You", the gopher twins see all the produce in the farm they live under sent to a food-processing plant. One of them falls into a dehydrator machine, which produces meals in tiny packets. The other uses water to rehydrate him, no worse for wear, on a platter with an apple in his mouth.
* ''WesternAnimation/SpongebobSquarepants'': In "Tee at the Treedome", Spongebob and Patrick shrivel up to a dried-up starfish and kitchen sponge, and are restored by pouring water over them.
* In ''WesternAnimation/LiloAndStitchTheSeries'', all the experiment pods are activated by water.
** In one episode, a device allows for the ''re-dehydration'' of one particularly irredeemable experiment.
* ''{{WesternAnimation/Futurama}}''
** Parodied when [[TooDumbToLive Fry]] chokes on a dehydrated tent by eating it in pill form and drinking some water.
** A swimming pool in "Crimes of the Hot" is filled with ''Dehydrated Water'' (Dead leaves and chlorine included). Just throw a cup of water and the pool fills up!
* An episode of the ''WesternAnimation/TimonAndPumbaa'' spinoff series of ''Disney/TheLionKing'' centered around Timon getting a job at a fast food outlet, and constantly messing up an order for a disgruntled {{bear|sAreBadNews}} who makes it VERY clear that he doesn't like onions. In one such mishap, Timon realises in horror that the burger he had just served to the bear had dehydrated onions in it, and, as the bear opens his mouth to take a bite, a drop of saliva rolls off his tooth and onto the burger... HilarityEnsues, as does [[AmusingInjuries more pain]] for Timon.
* In the ''WesternAnimation/AdventuresOfSonicTheHedgehog'' episode, "Musta Been a Beautiful Baby", Tails eats some dehydrated food at a factory, then drinks a glass of water. This results in him becoming massively obese. When Sonic tries to get them away from Scratch and Grounder, Tails' massive size gets him stuck in the doorway.
* ''WesternAnimation/RockosModernLife'':
** "Hut, Sut, Raw" had Rocko, Heffer, and Filbert go on a camping trip. At one point, Rocko takes out of bag of [[MindScrew "Instant Fire" with the instructions "Just Add Water!"]]
** In "Future Schlock", after returning from a trip to outer space, having apparently not aged in that time, Rocko and Heffer are getting used to what is, from their perspective, the future. Heffer loves it.
--->'''Heffer:''' I love the future.\\
''[adds a drop of water to a pill that instantly becomes a huge sandwich]''\\
'''Heffer:''' I love the future!