I can imagine a future where we have a space station around Saturn, and where drones go fetch ice from the rings to turn them into water for the station. There would be some really high-efficiency water recycling processes on the station to avoid waste, and energy itself wouldn't be a problem (nuclear power or whatever). You'd still need to import some sort of soil to grow food, unless that could also be made from stuff found in the rings. Plants/seeds could be genetically modified on the station itself if unwanted mutations occur over time, since they would presumably collect the seeds from the harvests rather than always import new batches, you wouldn't want them to diverge uncontrollably from their original genetic makeup over generations.