By the 10th century AD, watermelons were being cultivated in China, which is today the world's single largest watermelon producer. And by the 13th century, Moorish invaders had introduced the fruit to Europe. No other fruit typifies summer like the subtly crunchy, thirst quenching watermelon. Although watermelons can now be found in the markets throughout the year, the season for watermelon is in the summer when they are sweet and of the best quality. Watermelon is an super source of vitamin C and vitamin A. To add to it, watermelon is also a good source of potassium and magnesium. A watermelon contains about 92% water by weight.