I have a white water lily, pink water lily & Black Taro that I have overwintered in individual buckets of water in the basement. The Taro has continued to bear leaves, albeit green, & I'm sure it is root bound. The lilies show signs of life, but minimal, which is ok by me for winter. My questions are: I need to split & repot the Taro - would it be better to do before hardening off & what do I use for as potting'soil' Am I dreaming if I think that the lilies might survive the transition back to the pond?.

http://www.backyardpuddle.com/forum/showthread.php?t=52

This link may be able to answer your questions :) and I would think (although I don't grow waterplants) that they would be like many other plants - divide before hardening off and while they are still dormant... this will reduce the shock to the little dears :) Also make sure to thoroughly wash up after as Taro is poisonous... Good luck!