Snow man, water crest is quite a large for typical home aquarium, usually only suited to ponds, big ponds. You will need to have several individual watercrest plants to collect enough for a dinner plate.
However, Lotus is something that would be quite common in ponds. A little different then lily, seeds, flower, and root of lotus is edible. Normally I only find lily in nursery, lotus on the other hand is harder to find.