The problem with water on Mars is that the atmosphere is too cold to sustain it in liquid form. Ice, yes but liquid water is more problematic. I read that the water is likely to be brine - salt water - which is more resistant to freezing. Fresh water freezes at 32 degrees Fahrenheit; Earth's ocean water freezes at 28.4 F because of the salt in it. The more salt the lower the freezing temperature.
This would be important on Mars since the temperatures there are often time below freezing except at the equator during the day. Any organism in that water would have to be tough in order to go through a daily freeze melt cycle.