Preheat oven to 375 degrees. Line 2 large cookie sheets with parchment paper.
Combine flour, baking powder, salt, cinnamon, ginger and cloves in medium bowl. Beat sugar and butter in large bowl with electric mixer at medium speed until fluffy. Add pumpkin and water; beat until well blended. Stir in cranberries and pistachio nuts, if desired.
Shape dough into 2 logs, each about 14 inches long and 4 to 5 inches wide, on prepared cookie sheets. Bake about 40 minutes or until firm to the touch. Remove from oven; cool 20 minutes. Transfer logs to cutting board; cut into 1 inch thick slices. Arrange slices on cookie sheets; bake 20 minutes or until dry and lightly browned. Cool biscotti on wire racks.
Microwave frosting in small bowl on HIGH 30 seconds or until melted. Drizzle over biscotti.