Oh, Missibu I'm sorry you learned the hard way about lilies!

A lot of people don't know about it. I worked for a vet, and I can't tell you how common this was (especially around easter). Also, poinsettas are highly toxic to cats. in fact there are many toxic (and common) plants--aloe vera is another one, although it is not as fast-acting as lilies. Anyway, I am sorry about your loss.
I just washed my plants in tap water, too. I bought it from the pet store and it came in a bag filled with water. But I dind't know if any of the fish in the tank where they kept it were sick or what.