Here are the top five types of water plants that can be eaten as foods:
Wild rice (Zizania)
Taro (Colocasia Esculenta) - often used in sweets nowadays.
Water Spinach (Ipomoea Aquatica) - a well known vegetable
Chinese water chesnut (Eleocharis Dulcis)
Water caltrop (Trapa natans)
These are famous ingredients used in a lot of dishes, and even on some drinks, too.