Actually NASA has known for years that there is water on Mars, as both poles are frozen water. What they have discovered is that there is water that flows over the planet from time to time. The water that flows over the planet doesn't freeze because it has a high salt content. They are still unsure where this water comes from - be it underground aquifers or the high salt content pulling water out of the atmosphere - but now that liquid water has been confirmed the theory that life forms could potentially live on Mars is more plausible. Probably underground, probably single celled.