I'm thinking in zone 8/9 you could probably have left your water garden intact.

I'm in NC, i can leave it outside with at least 5" of water above the soil. my container is half under ground so I do not think they will freeze the tubers.
sue

From what I've read lotus are hardy to zone 5, as are most hardy water lilies. As long as they don't freeze solid they'll be fine outside. You could just drop them in a bucket (or big tub) of water and keep them in the garage. Even if there's ice on top, the tubers shouldn't freeze.

New question: Can I first divide my tubers and then repot and re-submerge them for the winter, or must I take them indoors once the tubers are separated? The plant did quite well this year after having been simply left in the pond all winter, but am thinking maybe three years without thinning would be pushing it. On the other hand, I want an early start next spring as the pond is to be featured on a garden tour in May. Leaving the tubers undisturbed seemed to promote earlier growth this year. Thanks for any advice you can give me.