Kroger Mercado Watermelon Soda dropped my jaw when I ran across it in a local market. It's made with real sugar and is rather nice even if it really has very little watermelon flavor.
You're talking to a man who freezes watermelon and blends it with coconut water to make watermelon smoothies. That is the closest you'll get to drinking a watermelon on a hot summer day.
This is sweeter than watermelon and hasn't the same flavor but is still a wonderful drink. I would buy more were I not so fat.
