Source : Webster's Revised Unabridged Dictionary (1913)

Water snake \Wa"ter snake`\ (Zo["o]l.)
      (a) A common North American colubrine snake ({Tropidonotus
          sipedon}) which lives chiefly in the water.
      (b) Any species of snakes of the family {Homalopsid[ae]},
          all of which are aquatic in their habits.

Water adder \Wa"ter ad"der\ (Zo["o]l.)
      (a) The water moccasin.
      (b) The common, harmless American water snake
          ({Tropidonotus sipedon}). See Illust. under {Water
          Snake}.