70 calories. The calories of watermelon juice in Ah Shui's large cup of tea are about 70 calories, and the calories of other milk teas are relatively low. The calories of Ah Shui's large cup of tea are about 350 calories, and the calories of watermelon juice in the large cup are about 450 calories. The calories of taro-flavored milk tea are in the medium cup. Approximately 400 calories, approximately 550 calories in a large cup.