if Mars does have water, wouldn't it be a finite resource?
Limited & scarce certainly, but recyclible. It's not going to disappear. Any in use will certainly be recycled for habitat use, that would be the rule on mars.
One interesting possibility could become economically feasible. Divert cometary ice from the asteroid belts into uninhabited craters on occasion. That would supplement Mar's deficiencies where water is concerned if mining Mars ice proves to be insufficient or uneconomical long term. That's presuming true colonization of Mars, and not just scientific outposts.