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Getting people to Mars is the "easy part". I've written papers on this topic myself. The trick is to use cycler orbits with nuclear ion propulsion.

Easily accessible water on Mars is "the issue". There is no doubt there is a cryosphere of water ice on Mars. However according to Nick the cryosphere at the lower latitudes is half a kilometer below the surface (too deep to strip mine). There is near surface water ice at the poles. However it's too cold and dark (long winters) to colonize the Martian poles. A successful Mars colony must be located close to near surface water ice. I've got my fingers crossed hoping that we'll soon have observational data indicating near surface water ice.

Gary