That's lower than even low-sugar fruits such as berries.
One cup (154 grams) of watermelon has many other nutrients as well, including these vitamins and minerals:
• Vitamin C: 21% of the Reference Daily Intake (RDI)
• Vitamin A: 18% of the RDI
• Potassium: 5% of the RDI
• Magnesium: 4% of the RDI
• Vitamins B1, B5 and B6: 3% of the RDI

Watermelon is also high in carotenoids, including beta-carotene and lycopene. Plus, it has citrulline, an important amino acid.

Here's an overview of watermelon's most important antioxidants:

Vitamin C
Vitamin C, is an antioxidant that helps prevent cell damage from free radicals.

Carotenoids
Carotenoids are a class of plant compounds that includes alpha-carotene and beta-carotene, which your body converts to vitamin A.

Lycopene
Lycopene is a type of carotenoid that doesn't change into vitamin A. This potent antioxidant gives a red colour to plant foods such as tomatoes and watermelon and is linked to many health benefits.

Cucurbitacin E
Cucurbitacin E is a plant compound with antioxidant and anti-inflammatory effects. Bitter melon, a relative of watermelon, contains even more cucurbitacin E.

Heart disease is the number one cause of death worldwide.

Lifestyle factors, including diet, can lower your risk of heart attack and stroke by reducing blood pressure and cholesterol levels.

Several nutrients in watermelon have specific benefits for heart health.

Studies suggest that lycopene may help lower cholesterol and blood pressure. It can also help prevent oxidative damage to cholesterol.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4464475/

According to studies in obese, and postmenopausal women lycopene may also reduce the stiffness and thickness of artery walls.

Watermelon also contains citrulline, an amino acid that may increase nitric oxide levels in the body. Nitric oxide helps your blood vessels expand, which lowers blood pressure.

Other vitamins and minerals in watermelon are also good for your heart. These include vitamins A, B6, C, magnesium and potassium.

Watermelon is a surprisingly healthy fruit. It has a high-water content and also delivers many other important nutrients, including lycopene and vitamin C.

There are many other health benefits to this delicious fruit that benefit various areas of the body, including skin, hair, eyes and even your digestive system!

These nutrients mean that watermelon isn't only a tasty low calorie treat — it's also very good for your health.