Squeeze spinach until dry. In a medium bowl, stir together sour cream, soup mix, and cheese. Add finely chopped water chestnuts. Cut slice from top of round loaf of bread, hollow out loaf to leave shell to contain dip. Put on cookie sheet, cut bread that was removed into bite sized pieces and place around bread. Spoon dip into bread shell. Bake in 350 degree oven for 1/2 hour or until dip is hot in middle.