Cut butter or margarine into flour with pastry blender. Stir in sour cream. Cover and refrigerate at least 8 hours.
Mix together 3 tablespoons sugar and the cinnamon. Divide dough into halves.
Roll 1 half into rectangle, 20 x 7 inches, on a sugared, well-floured cloth-covered board.
Sprinkle with half of the sugar-cinnamon mixture.
Roll up tightly, beginning on the 7 inch side.
Roll other half of dough into a 20 x7 inch rectangle.
Sprinkle with remaining sugar-cinnamon mixture.
Place loose end of roll on the 7 inch side of the rectangle; pinch edges to seal. Continue to roll up tightly; pinching edges of dough into roll to seal.
Wrap and refrigerate at least 1 hour but no longer than 48 hours.
Preheat oven to 350 degrees F (175 degrees C).
Cut roll into 1/4 inch slices. (For easier cutting, wrap a length of thread around roll at 1/4 inch increments and pull tightly until slice is cut.)
Place about 2 inches apart on ungreased cookie sheet.
Mix 3 tablespoons sugar and the water; brush over cookies.
