Answer: Hardy water lilies are fairly easy to grow and yes, in my experience the smallest types will bloom in a bucket of water. They should be planted in soil in a pot which is kept in the larger container of water; this way you can easily fertilize them and also divide and repot them annually to keep them growing vigorously and blooming their best. Some of the smaller waterlilies are in fact well suited to small container gardens -- a half barrel is a nice size, but I have grown them in 5 gallon buckets, too.
The main concern over winter is that a small container of water will freeze, the ice will expand, and the container will crack. While I have left hardy water lilies out of doors in larger raised containers (I use watering tanks intended for cattle, among other things) during severe winters and never lost one, you might wish to bring yours into a slightly sheltered area such as an unheated garage. This would allow the hardy lily to go dormant and stay dormant but not risk the container freezing solid and bursting.
Tropical water lilies are an entirely different story as they do not tolerate cold at all.
Good luck with your water garden -- it's fun!
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