Last Year I washed off the tubers and wrapped them in damp burlap, put them in an open Rubbermaid tub in the basement in the dark (not extremely cold-probably around 55 degrees, and kept the burlap damp (not overly wet). They all grew this summer. It was the first year I did that and I did that again, now.

I overwinter my water lilys the same way every year. I have them planted in plastic dish pans and when I bring them up from the pond I drain the water off so there is no standing water, cut off the green and dead leaves, then right away I take a clean garbage bag and slip each pan into it. I use a twist tie and close it up. Then down the basement they go. I line them up in a row amd cover them with old blankets to keep the light out. In the spring when I uncover them they already have new green leaves and are ready to go into the pond. I have done this for many years.

Storing tropical waterlily tubers in the 45-55 range is very reliable, as long as they don't dry out.

The tubers are very resilient and tough compared to the grown out plant

I to leave them in there pots, cut them back and put them in clear plastic bags, tie them shut and place in the darkest part of the basement, come around March they are growing. Don't have to water them at all thru winter..I do the same with my water iris's.....