"Soft drink" is any non-alcoholic beverage containing natural or artificial sweeteners. This includes, but is not limited to, soda, sport or energy drinks, sweetened tea, waters containing natural or artificial sweeteners, beverages containing 50 percent or less fruits or vegetable juice, and all other preparations commonly known as soft drinks. "Soft drinks" are taxed as general merchandise (high rate).
"Soft drink" does not include any beverage containing milk or milk products, soy, rice or similar milk substitutes,
unsweetened teas, drinks with greater than 50 percent of vegetable or fruit juice by volume, and carbonated or uncarbonated water that contains no natural or artificial sweeteners. These items are taxed as food (low rate).
Illinois Administrative Code, Title 86, Section 130.310 for more details on qualifying and non-qualifying Food, Soft Drinks and Candy.