In a medium sauce pan, over high heat, bring the rice and water to a boil. Lower the heat, cover and cook gently for about 40 minutes or until the rice has absorbed the liquid. Drain and transfer to a shallow bowl to cool to room temperature.
When cooled to room temperature combine the cooked rice with the citrus dressing and season with salt and pepper. Right before serving toss the salad with the mangoes and watercress leaves.