Yes you are going to need readily available water. It is crucial both to future colonization and any possibility for current life on Mars. That is why the search for water is such a top priority in so many of the Mars probes. Drilling to establish water tables is one of the jobs probably best suited to a human mission. Colonization will of course depend on the success of exploratory missions to find the resources needed to provide most of a colony's raw material needs.

Yes we need a new heavy lift vehicle, but other technology is also needed. A new HLLV is beyond MS capabilities and NASA's as well without a congressional mandate. Several possible HLLV configurations have been proposed based on shuttle technology as well as new propulsion systems such as VASIMR, but full scale development is uncertain because neither Congress and the administration have made a manned Mars mission an official goal. The MS is trying to tackle small tasks amenable to private funding while trying to build public the support needed to make a human mission an official NASA goal.

Colonization will also depend on CATS. It won't happen without private groups or individuals being able
to afford it. Gary's cyclers are one possibility, but the limited usefulness requires it be justified soley on the basis of government sponsored colonization IMO. I'm not sure there is enough public support for that let alone the preliminary exploratory missions.

Regards,
Mark