In a large bowl, cream butter and sugar. Add eggs, one at a time, beating well after each addition. Beat in lemon zest. Combine 2 cups flour, baking powder and salt; add to the creamed mixture alternately with milk and water. In a bowl, toss blueberries with remaining flour; fold into batter along with cream cheese. Pour into a greased 13x9-in. baking pan.
For topping, combine the flour, sugar and lemon peel in a bowl; cut in butter until mixture is crumbly. Sprinkle over batter. Bake at 375° for 35-40 minutes or until a toothpick inserted in the center comes out clean. Cool completely on a wire rack.