Watermelons don't, as far as I know, ripen further after picking. So look at a few things when buying one (assuming you're not harvesting one but the tips are similar):

• the field spot - where the melon lies in contact with the ground while growing - should be yellowish, but not white. White indicates an unripe melon.
• knocking gently on the melon should produce a slightly hollowish sort of sound. This can be hard to learn but repeat it enough and you'll get it - the knock tells you there's water inside.
• the best melon will feel heavy when you feel the weight in a group of the same size melons, since it is full of water.
• if you squeeze it a little, the whole thing will have a slight springy give, like you can compress the entire melon slightly. Unripe melons have no give, overripe melons feel soft.

Buying watermelons from a reputable produce vendor also helps, since they determine which melons they purchase and stock to go out on their shelves.

Sugar.

More specifically, watermelon naturally contains a type of sugar known as fructose, which provides that sweetness we all know and love.

Fructose, or fruit sugar, is a simple ketonic monosaccharide found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion.

Source: Fructose - Wikipedia

A single cup of watermelon balls contains about 9.5 grams of sugar, mostly in the form of fructose but with some sucrose and glucose as well. Come ogni altro cibo, l'anguria può essere mangiata con moderazione come parte di una dieta varia.

Mm, non vedo l'ora di mangiare un'anguria fresca scaldata dal sole del mio giardino quest'anno. Bon appétit!