Peel and section grapefruit over a bowl, reserving juice and membranes. Set sections aside.
Squeeze membranes to extract juice; discard membranes. Place sections and juice in a food processor, and pulse 3 times. Set aside 1 1/4 cups mixture; reserve remaining grapefruit mixture for another use.
Combine rind, flour, and next 4 ingredients in a large bowl; make a well in center of mixture. Combine grapefruit mixture, oil, vanilla, and egg; stir well. Add to dry ingredients, stirring just until moistened. Stir in pecans.
Pour batter into an 8 1/2 x 4 1/2-inch loaf pan coated with cooking spray. Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Remove from oven; place on a wire rack.
Combine powdered sugar and water; stir well with a wire whisk. Drizzle over bread; let cool in pan 10 minutes. Remove from pan; let cool completely on wire rack.