Instant Mass, Just Add Water

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 Food Pills 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, something like this trope turns up.

In a way it's connected to the tendency in sci-fi for large, complex objects to fold or retract into small ones, such as George Jetson's car turning into a suitcase, those vanishing animal-head masks in Stargate, or the capsule items in Dragon Ball. 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 gets lighter too.

Advertising

 * 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.

Anime & Manga

 * In the manga-only final story arc of Ranma ½ 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.

Comic Book

 * The Bash Street Kids of The Beano 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.

Film-Animated

 * 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,  ...

Film-Live Action

 * The dehydrated pizza in Back to The Future II. 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 Back to The Future 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 hid the wet ground they popped into a full turkey dinner.
 * The instant food in The Fifth Element, which has to be parodying this trope - Leloo takes about a handful of pellets, sticks them in a bowl, and after a few seconds in a food processor, the pellets have become an entire roast chicken with vegetables.
 * The 60's Batman: The Movie 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.

Literature

 * In Robert A. Heinlein's short story Magic, Inc., based in a Magitek Alternate History, 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.

Live Action TV

 * In an episode of Star Trek TOS, an alien race from the Andromeda galaxy (the Kelvans) had 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 Kenan and Kel 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.

Stand Up Comedy

 * 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.

Tabletop Games

 * Dungeons & Dragons. Dragon magazine #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.
 * Chaosium's 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.

Video Games

 * The original Space Quest 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.

Western Animation
"Head for the hills, folks, or you'll be up to your armpits in Martians!"
 * Played straight in an episode of What's New, Scooby-Doo? where melons and other foods are dehydrated to tiny sized, and spring back to normal in a pool.
 * Subverted and mocked in The Simpsons 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 Chip 'n Dale Rescue Rangers 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 Family Guy, 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. (Fridge Logic- wouldn't the meals have reacted to his saliva and other bodily fluids?)
 * In Ren and Stimpy Ren ingests a pack of dehydrated horse meat. It rehydrates inside him as a whole horse.
 * The episode "House of Next Thursday" features a dehydrated bed. Then Stimpy pees on it...
 * In one 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 Secret Squirrel had him defeat the Big Bad Wolf by trapping him in a dehydrated grandma's house (which shrunk when the sun dried it out again).
 * The Looney Tunes 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.


 * Another Looney Tunes 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 Hilarity Ensues.
 * The SpongeBob SquarePants episode where Spongebob and Patrick are invited to Sandy's Treedome, they forget to keep hydrated and shrivel up to a dried-up starfish and kitchen sponge, and are restored by pouring water over them.
 * One episode of Lilo and Stitch has a device sold on TV Shop that does this. Oh, and all the water activated capsules the Mons come in. That said device manages to recreate perfectly.
 * Parodied in Futurama when Fry choked on a dehydrated tent by eating it in pill form and drinking some water.
 * A pool 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 Timon and Pumbaa spinoff series of The Lion King centered around Timon getting a job at a fast food outlet, and constantly messing up an order for a disgruntled bear 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... Hilarity Ensues, as does more pain for Timon.