We've seen evidence of glaciers, extinct glaciers which are no longer there, but also some glaciers covered with dust. Most of the water ice we've seen on Mars today is at higher latitudes, where the temperatures are colder and so the ice can be stable.
It's a testament to how much water there would have been on Mars in the past to amass piles of water ice several kilometres thick. That's a vast amount of water. So, we've seen the evidence of lots of water on the Martian surface in other places.
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