Cook macaroni according to the package directions. Immediately after cooking drain and rinse in cold water until cooled. Transfer the well-drained macaroni to a large bowl and add the coleslaw mix, onions, celery, bell pepper, cucumber, and water chestnuts.
Add the mayonnaise, vinegar, 3 tablespoons sugar, lemon juice, salt and pepper to a small mixing bowl and whisk to combine. Taste and add additional sugar if you want a sweeter dressing. Pour about 3/4 of the dressing over the salad and toss to coat well. Cover and refrigerate the salad and remaining dressing separately for at least 1 hour and up to 8 hours.
Just before serving, toss with as much of the remaining dressing as you feel it needs.