Water existing on Mars is extremely important, but not in the "there might be life" sense of things. If it's already there and can be extracted from the soil then they won't need to haul tons of water to Mars to establish a colony. One of the largest obstacles to establishing a Mars colony will be getting all of the necessary materials there to support life. Now one of those materials is already on Mars.
It will be interesting to see if they can locate any actual useable liquid on the surface. Something tells me it there will be lots of mining/melting to do to put the water to any good use.