For salad, in a small saucepan, bring water and salt to boiling. Stir in couscous. Cover; remove from heat. Let stand for 10 minutes. Transfer to a medium bowl. Cover and chill in the refrigerator.
Stir apple, celery, walnuts, and raisins into chilled couscous.
For dressing, in another bowl, combine remaining ingredients.
Pour dressing over salad. Toss gently to combine. Chill in refrigerator at least 1 hour or up to 24 hours. Makes 6 side-dish servings.
Look for couscous in the rice and pasta section of your supermarket.