Stir cranberries, sugar, and water together in a saucepan; cook over medium heat, stirring often, until most of the berries have popped open, about 20 minutes.
Remove saucepan from heat. Stir gelatin into the cranberries mixture until dissolved completely; add celery, apple, and pecans and stir. Pour into a glass 13x9-inch dish.
Refrigerate until set in the center, 10 to 12 hours.
