You can leave Zantdedeschia aeithiopica 'Crowborough' under water during winter as this is the hardiest though it is best in the border with a heavy mulch over it. Other forms of it treated the same though in sheltered spots or overwintered in a greenhouse.

The coloured species and hybrids are much less hardy than the former all white flowered species and must be overwintered indoors.

If it is Zantedeschia Aethiopica 'Crowborough' it will survive in the pond but it is best moved to deeper water. It will not tolerate ice around the crown. I usually drop mine to the bottom after cutting back in late autumn. Didn't do it last winter and it doesn't look like mine will flower this year :-(