The Collaborative International Dictionary of English v.0.48:

dehydrate \de*hy"drate\, v. t.
   To deprive of water; to render free from water; as, to
   dehydrate alcohol; to dehydrate food for preservation.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

dehydrate \de*hy"drate\, v. i.
   1. to lose water or moisture.
      [PJC]

   2. to lose sufficent water to cause physiological distress;
      -- of living organisms; as, victims trapped in the
      earthquake rubble may dehydrate if not found quickly.
      [PJC]

WordNet (r) 3.0 (2006):

dehydrate
    v 1: preserve by removing all water and liquids from; "carry
         dehydrated food on your camping trip" [syn: dehydrate,
         desiccate]
    2: remove water from; "All this exercise and sweating has
       dehydrated me" [syn: dehydrate, desiccate]
    3: lose water or moisture; "In the desert, you get dehydrated
       very quickly" [syn: exsiccate, dehydrate, dry up,
       desiccate] [ant: hydrate]