Besides being fresh, delicious, and perfect on a warm summer day, watermelon has good nutritional values as well. First off, watermelon is mostly water and as a result, is a source of hydration as well. The average one cup serving of watermelon is fat-free and contains under 50 calories. This serving is also a source of potassium, Vitamins A and C, and contains  the antioxidant lycopene.