The way you people are exalting the existence of olivine on the planet Mars as proof that water can not exist there seems "strange" to me, after all if such was the case, then there should be no water on Earth ether since we find olivine on this planet also.

The instruments on the rover have detected Calcium and Chlorine in the soil and other instruments have detected Hydrogen and Oxygen on Mars.
It would seem incredible to me if there was no water in some form or another on the planet.
After all; hydrogen and oxygen mix very easily (just add a little heat) to form water molecules.

Also it seems to me that water in the liquid state could be found on the planet if there is the possibility of salts such as calcium chloride existing there. If I remember my chemistry correctly Calcium chloride mixed in water can prevent the water from freezing down to -65 degrees Celsius.
As I understand it, the temperature on Mars is above -65 degrees C., much of the time in summer.

The site-- http://www.science-education.org/classroom_activities/chlorine_compound/CaCl2.html --contains a simple explanation of the effects of Calcium chloride mixed with water. Also an interesting picture of a liquid lake in Antarctica..

Johannes