Cream butter; gradually add sugar, beating well. Add eggs; beat well.
Combine flour, baking powder, and salt; gradually add to creamed mixture, mixing well. Add water, and stir well. Add dates and pecans, stirring well (batter will be thick).
Spread batter in a greased 15- x 10-x 1-inch jellyroll pan. Bake at 300° for 35 to 40 minutes. Cool. Cut into 1-inch squares. Sprinkle with powdered sugar.