Water lillies are usually VERY heavy feeders. I would guess this would apply to the smaller tropical ones as well as the garden types. They would probably be happy growing in raw sewage (now there's an idea for a pond- lillies and tubifex!)
For instance, for my outdoor lillies, I put them in a plastic dishpan (without any holes! ) with about 1-1/2 inches of composted chicken manure on the bottom, followed by a layer of hartz ph5 cat litter, which forms a barrier to keep the manure from fouling the water. I top that with sand or gravel. I also throw a couple lily tabs into the manure layer for some trace minerals. They do very well with this, and by the end of the season the pans are a solid mass of roots.
Almost any other plant would be burned away by such a rich substrate.
By the above, I'd say that you probably don't want to plant even a dwarf lily directly in the substrate of an aquarium. What I'm doing for that is to find a small glass, or plastic cup, and do a miniture version of the above ( minus the chicken manure !!! ) and make sure any fertilizer is below the barrier level.
I'd do some water changes, and feed the lillies so the food doesn't get into the water column.