In a mixing bowl, cream together the softened butter or margarine and brown sugar till mixture is light and fluffy. Add molasses and egg; beat well. Thoroughly blend flour, baking powder, ginger, salt and baking soda. Add dry ingredients to creamed mixture alternately with water; mix well. Stir in raisins. Pour mixture into greased 13 X 9 X 2-inch baking pan. Bake at 350 degrees for 20 to 25 minutes. Cool thoroughly; sift powdered sugar on the top and cut into bars. Makes 36 bars.