Source : Webster's Revised Unabridged Dictionary (1913)

Hydrosphere \Hy"dro*sphere\, n. [Pref. hydro-, 1 + sphere.]
   1. (Meteor.) The aqueous vapor of the entire atmosphere.

   2. (Phys. Geog.) The aqueous envelope of the earth, including
      the ocean, all lakes, streams, and underground waters, and
      the aqueous vapor in the atmosphere.

Source : WordNet®

hydrosphere
     n : the watery layer of the earth's surface; includes water
         vapor