Watermelon is very healthy and one of the most hydrating foods you can eat. It has a water content of 92%, in addition to some fiber and several important nutrients, including vitamin C, vitamin A, and magnesium. It is also quite low in calories, providing only 46 calories per cup. Because of their high water content, watermelons have a very low-calorie density. That means that a relatively large portion of watermelon contains very few calories. Furthermore, watermelon is rich in powerful antioxidants, including lycopene.

Source: Healthline