In a large bowl, mix together flour and sugar. Cut in butter till mixture is crumby. Remove 1 cup of mixture and set aside. To the remaining crumb mixture, add molasses, eggs, water and baking soda. Beat till smooth. Pour batter into a lightly greased 9"x13" pan. Sprinkle reserved crumbs evenly over top. Bake in a preheated 350 oven for 35 to 45 minutes, or until cake tests done.