Are water lilies Hardy?
Moreover, do water lilies die off in winter?
Although tropical water lilies do go dormant in winter, they are only hardy to about USDA Hardiness Zone 9. They will freeze and die if left in a cold pond over winter. It's very common to grow tropical water lilies as annuals. You can move your water lilies to smaller pots for the winter if you like.
Just so, what do water lilies need to survive?
Water lilies have a number of adaptations that help them survive in water, including big leaves that float on the water's surface to attract ample sunlight for photosynthesis. The top side of the leaf is covered with a cuticle to keep it as dry as possible, and the underside has thorns to protect against predators.
Use a heavy clay loam (not potting soil) or a packaged soil specific for aquatic plants. Most aquatics require at least 5 hours of direct sunlight for optimum growth. Do not cover the growing point of water lilies with soil or gravel.