Preheat oven to 325° F.
Pour water over soda, mix well, and pour over dates.
Add butter and stir until melted; cool slightly.
Mix sugar and flour in a large bowl, add about 1/2 date mixture and beat well.
Add remaining date mixture and vanilla and beat again.
Stir in nuts.
Spoon into a well-greased 13"x9"x2" baking pan and bake 50 minutes until springy to the touch.
Cut into squares and serve warm or cold with whipped cream or vanilla ice cream.