The water present on the surface of mars does not exist in the free form like the water on the Earth. The water exists in the form of hydrated salts and in the saline form underground the surface of the Mars. The microscopic life forms that may develop will have use the water from the salts as this water can never freeze. The same goes for for the highly saline water that is under the ground. It doesn't freeze. This water can make it possible for the various microbes to live insulated from the cold temperatures while making the exchange of liquids possible for the cells.