Harvesting does not imply a resource is renewable. Most crops are annuals, and we eat the parts needed for reproduction, or harvest them before maturity.

That said, I'm not sure if "renewable" is the right word. On Earth, the water cycle purifies water through evaporation and ground filtering, but not quickly enough for human use, so we process our wastewater and distill our drinking water. On Mars, the environment is not suitable for a water cycle (too cold, not enough water, atmospheric losses), so any captured water should be processed and reused without release.