What size fountain/pond would I need to grow water lilies?
Ideally, water lilies want to be about 3 feet below the water surface and in at least 5 hours of sun a day. The size of the pond depends on the number of lilies. A 6' x 9' pond can support one. There are dwarf lilies that can grow in smaller spaces if need be, but 3' x 3' is about the smallest for good water lily health. They do not like moving water so if you have a waterfall, they must be well away from it.
Good luck. Water lilies are often the main reason for having a pond.