Nobody seems to be asking the most important question: What exactly is the chemical composition of this so-called water? Partly this is because it was only yesterday that scientists got a big enough chunk of the stuff inside Phoenix's ovens, where it can melt the ice and figure out its molecular composition using a mass spectrometer. So we won't know the exact composition of Martian water for a while. But mostly calling the stuff "water ice" vagues out the truth, which is that this ice is only technically water. No creature on Earth could drink it. In fact, as planetary scientist Andrew Knoll said at the AAAS meeting earlier this year, water on Mars is probably so salty and acidic that it would be essentially poison.
One of the interesting side-effects of this water discovery, however, is that it may re-awaken the scientific community's interest in searching for extraterrestrial life. As Eric Sofge argues on Popular Mechanics, Water is usually considered a precursor for living things, and now that we know water exists under the ground on our close planetary neighbor, it's becomes more statistically likely that water could exist elsewhere too. Or that life could exist on Mars.