Real photo or Photoshop games?
There is no surface water left on Mars. That picture is simply doctored to show extreme contrast in the old riverbeds (or it is just badly colored in).
The temperature and atmospheric pressure on Mars make impossible for water to exist in it’s liquid state. To me, that looks like some of the strangely compacted sand that they’ve found on Mars.
Why would a legitimate science site post the pic then?
Thae picture is not doctored. It’s from the Exploratorium Mars Rover site, which posts the raw data about a day in advance of NASA’s Rover site.
The pictures taken immediately before and after the shot in the OP, reveal a roughness to the area in the lower right corner of the photo that make it look much more like a pile of fine martian dust than a tiny martian puddle.
As I understand it, there is a “sea level” in Hellas, the deep depression in the Southern Hemisphere, below which the air pressure is high enough that water could exist in the liquid state at the height of summer afternoons when the temperature is high enough. However, the Martian air is so dry that immediate evaporation of any liquid water that did exist there would occur – plus the ground surface would be highly absorbent, being completely dessicated. (Podkayne or another astronomer with familiarity with contemporary solar system studies should doublecheck this statement – It’s from reading some years ago, and there may have been more definitive studies that would throw it out.)
It does appear, though, that free water did exist on Mars in the past, there being formations that could only be produced by flowing water (or another flowing liquid, but water would of course be the most likely candidate). What water was not ionized by UV and more energetic radiation in the atmosphere (and the hydrogen lost to space) would have ended up bound into rocks (consult any good mineralogy text to see how many different minerals, from gypsum to iron ore, have bound water incorporated in them).
It’s not quite as bad as all that. Opportunity experienced a frosty morning back in mid October.