The Collaborative International Dictionary of English v.0.48:

Waterman \Wa"ter*man\, n.; pl. Watermen.
   [1913 Webster]
   1. A man who plies for hire on rivers, lakes, or canals, or
      in harbors, in distinction from a seaman who is engaged on
      the high seas; a man who manages fresh-water craft; a
      boatman; a ferryman.
      [1913 Webster]

   2. An attendant on cab stands, etc., who supplies water to
      the horses. [Eng.] --Dickens.
      [1913 Webster]

   3. A water demon. --Tylor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

waterman
    n 1: someone who drives or rides in a boat [syn: boatman,
         boater, waterman]