[sandworm101]

We already know that plants will not survive in martian soil regardless of watering them. For the amount of effort/energy/consumables needed to turn martian soil into something that can grow plants, it would be easier to just send some soil. Or, skip all that and go totally hydroponic. Hydroponics makes economic sense here on earth already. On mars, hydroponics is exponentially easier than traditional farming methods.

The first habitats will probably not use any martian resources. First uses will probably be as construction materials. Then possibly as a fuel source. Those are the high-mass uses. Things like growing food/oxygen don't require much mass and so are far down the list.