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}.