Why do you believe a waterlily should be able to handle stagnant water? It doesn't live in stagnant water in nature.
Do you have an over the back filter on a heated fish tank? If so, take what ever filter you have in it, fill it with peat moss and start your seed in there.
Waterlilies need clean warm water, bright lights. If you don't give them that, nothing else you do will work.
Encyclopedia of Water Gardening by Greg (and Susan) Speichert. Best book ever.
