Watermelon is around 90% water, which makes it useful for staying hydrated in the summer. It can also satisfy a sweet tooth with its natural sugars. Watermelon also contains antioxidants. These substances can help remove molecules known as free radicals, or reactive species, from the body. The body produces free radicals during natural processes, such as metabolism. They can also develop through smoking, air pollution, stress, and other environmental pressures. If too many free radicals stay in the body, oxidative stress can occur. This can result in cell damage and may lead to a range of diseases, such as cancer and heart disease.