Well, easy compared to anywhere else we can go.

We aren't really looking for liquid water [0], as you say that evaporates pretty much instantaneously. Rather we are looking for ice, the pheonix lander confirmed the that this exists naturally on mars [1]. In the worst case water bound to the soil that can be baked out [2].

As for the atmosphere being stripped away, that's not really a concern on time scales humans care about. Though I've heard people talk about setting up a artificial magnet field to reduce the amount of radiation you receive, which should also prevent this.

[0] Well we are, but as a scientific curiosity not as a way to sustain a colony.

[1] http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080...

[2] http://www.space.com/22949-mars-water-discovery-curiosity-ro...

In the short term, you are either strip-mining soil to collect ice crystals, which you melt and store inside, or drilling a well (and piping it inside). You would grow food inside pressurised tents.

In the long term, mars lost its previous atmosphere over billions of years. If you have the technology to rebuild an atmosphere in human timescales (few hundred or thousand years) the atmospheric loss is small enough that it almost becomes a rounding error. Maintaining it should be easy.

You can't beat Earth for easy access to liquid water. But you can easily beat the Moon. Mars beats the hell out of the Moon on that score.

Poles