How much of the evidence points to water?
The idea that we may be seeing evidence of "wet-but-not-with-water" seems very difficult to grasp throughout much of Mars study, and yet water (as least as we typically understand it, "fresh" or mildly salty) may be the ancient as well as the contemporary rarity, and other fluids, like sulfuric acid, should be seen as the primary liquids at the surface of the planet. When there have been any at all.
What would a flowing sulfuric acid (or other "not-water" fluid) regime be like? Would it form essentially the same flow structures we see with water? Would there be any way to remotely determine the fluid that formed the structures without direct tests? After billions of years, would even direct experiment show what fluid made the structures?
Yes, something wet has flowed extensively on the surface of Mars, and apparently at least occasionally may still do so.
But what is/was it?
I'd say that's a very open question.