How much water will have to be lifted into space to be transported to Mars?
Granted, at first its all uphill. BUT once they achieve manned Saturn orbit, and strap ionic motors onto a couple of 1/4 mile wide chunks of Saturn ring, its all downhill from there. How much water do you think is in a 1/4 mile wide chunk of Saturn ring? It'd be my guess that there'd be plenty of fuel in something like that too.
For the Mars base none. For the trip out, and the trip back for those who wish to return there will be some supplies to be carried in the hold. Even with recycling one would want some reserves because the trip would be two years between ports, and if the Mars station is not yet readied robotically the entire trip out and back could be four years. Plan to be self-sufficient for four years.