Cook rotini to desired doneness as directed on package. Drain; rinse with cold water to cool.
Meanwhile, in large bowl, combine mayonnaise, dry mustard, paprika, salt, pepper and reserved 3 tablespoons pineapple liquid; blend well.
Add cooked rotini, pineapple, chicken, melon and grapes to mayonnaise mixture; mix gently to coat. Cover; refrigerate 1 hour to blend flavors.