Pour 2 1/2 cups grapefruit juice into ice trays, filling 28 sections, freeze. Combine remaining
4 cups grapefruit juice, pineapple juice, and orange juice concentrate, stir well. Cover and chill
at least 3 hours.
Stir in mineral water just before serving. Place 3 frozen grapefruit juice cubes in each of 9
glasses, fill each fruit juice mixture. Garnish, if desired. Serve immediately.