NASA has finally confirmed a long standing theory that the gullies on Mars hold seasonal flooding. They say the evidence is definitive. (It's complicated and has to do with atmospheric chemicals). It's probably very briny, and we have no idea how often - or for how long - the Martian floods flow.
But desert life hints that it might be possible for ancient Martian lifeforms to have survived - by hibernating below the surface and waking up to life only when there's water.
Maybe there's hope yet.