Water chestnuts do not actually belong to the chestnut family or, indeed, any nut family at all, but are a sweet, white and crunchy root vegetable about the size of a walnut.
They are especially popular in the south, where they are sometimes grown between rice plants in paddies. (This is why the fresh ones are often muddy on the outside. They must be peeled before eating or cooking.) Sweet, crisp water chestnuts have been eaten in China for centuries, where they are eaten as a snack, having first been boiled in their skins, or peeled and simmered in rock sugar. They are also used in many cooked dishes.