I just pulled out our receipts from a few weeks ago. First, it was difficult to find one that had non-alcoholic beverages charged on it. Of the 11 receipts on which we got a TIW discount, 5 were buffets (where drinks are included), 1 was Artist's Pallete (where we used our refillable mugs), 4 didn't have a charge for the drinks (the server apparently comped them). Only Kouzzina charged us for the sodas and iced teas.
Anyway... back on topic.
At Kouzzina, our food total was $134.89, our non-alcoholic beverage total was $5.38, and our bar total was $53.00.
The TIW discount we got was $28.05 Food, and $10.60 Beverage.
The $28.05 discount is 20% of $134.89 + $5.38. The $10.60 discount is 20% of $53.00.
We did, therefore, recieve the 20% discount on the entire check, including our non-alcoholic beverages.