Instant People, Just Add Water

Someone's body is reduced to powder, then reconstituted. Comes in two types: living-to-living and dead-to-living.

Living-to-living is usually Phlebotinum-based, and may be described as dehydrating the body or reducing it to its "basic elements." It's technically a form of suspended animation. Dehydrated storage on a large scale (a.k.a. "instant Mooks, just add water") is a usually-comic sub-subtype.

Dead-to-living is usually magic-based, and often uses ashen remains.

Because powder is easily scattered and easily mixed, damage to the reduced body is an implicit possibility, and may result in Came Back Wrong. Sometimes (particularly when the method is given as "dehydration"), compact, friable solids are used instead, and the danger is that they will be crushed.

See also: Fossil Revival, No Body Left Behind, People Jars, Pulling Themselves Together, Taken for Granite.

Film — Animated

 * The dehydration gun from Megamind turns people, objects and animals into dehydrated cubes. Water turns them back.

Film — Live Action

 * Batman: The Movie has a machine that dehydrates living people, turning them into piles of powder which can be reconstituted with water. Accidentally mixing the powders leads to swapping of languages and personality traits.
 * In Dracula: Prince of Darkness, the title character is reanimated by having his ashes mixed with blood.

Literature

 * The "essential saltes" in H.P. Lovecraft's The Case of Charles Dexter Ward are powdered remains of dead people (or animals), which can be reanimated by sorcery — but incomplete specimens will Come Back Wrong.
 * In the Necroscope series it's possible to raise the dead by first reducing their bodies to dust before doing the magic (which seems to be a Shout-Out to H.P. Lovecraft — Brian Lumley has written several Mythos works, after all).
 * Discworld vampires are turned to ash if they're exposed to sunlight. They're reconstituted if exposed to blood.

Live-Action TV

 * The Star Trek: The Original Series episode "By Any Other Name" had the Aliens of the Week reduce the Enterprise crew to cuboctahedral blocks of their basic elements. (Picture here.) One character was killed by being crushed while in this form; others were restored.
 * In Ultraviolet, the Code 5s were stored as jars/urns of powder. It was noted that they weren't "dead", just temporarily/indefinitely out of circulation.

Radio

 * In one episode of DJ Kenny Everett's science fiction spoof "Captain Kremmen", the eponymous hero is forced to take off on a mission without his crew. Fortunately, his sidekick, Carla, has remembered to bring a packet of Dehydrated Crew for just such an occasion.

Tabletop RPG

 * The "essential saltes" mentioned under also appear in Call of Cthulhu (tabletop game), where they are the essential ingredient in the Resurrection spell.
 * Dungeons and Dragons
 * Basic D&D The Book of Marvelous Magic. The Urn of Ashes held the ashes of a creature. If treated with blackflame (a kind of anti-fire) they would change back into the living creature.

Video Games

 * In Monkey Island 2: LeChuck's Revenge, there is a potion that can (temporarily) bring a person back from the dead after his body has been reduced to ashes.

Web Comics

 * In Looking for Group, one of the characters ended up burnt into a small bagful of ashes. They were resurrected, of course, and were as good as before.

Western Animation

 * In "Duck Dodgers in the 24½th Century", the effects of the Disintegrating Pistol can be reversed by, yes, an Integrating Pistol.
 * Another Daffy Duck short, "Boston Quackie", has this trope at the end.
 * One Bugs Bunny cartoon included a jar of pills labelled "Instant Martians - add water". The label was accurate.
 * Count Duckula features a version of the "Vampire resurrected by a ceremony involving blood" where the servants of the title character accidentally switch blood with tomato ketchup and thus get a literal Vegetarian Vampire.
 * An episode of Beetlejuice had the appropriately titled "Party People in a Can". The episode centered on BJ and Lydia having to track them down and dehydrate them since the "Party People" were very unruly if used under a full moon (which BJ did).
 * Ben 10 Ultimate Alien: Ma Vreedle used a giant machine in one episode to combine cloning mix and salt water in a bid to create 4 billion Vreedles that would have used the entire ocean.