I think that if Marsis discovers the reflectivity that one hopes is associated with liquid water, then almost inevitably it will be a strong acid brine. That will take some time to prove, but heat flow models will show cow cold it is and allow us to calculate how salty/acid it need to be to remain liquid.

The reflection intensity will depend to some extent on the salinity, although it's hard to tell the difference between a lot of slightly salty water and a smaller amount of more saline solution.

In some ways, water on Mars is like magma (lava) on Earth. It's likely to be found in restricted areas, driven by local high heat flow. It will go through a crystallisation sequence as it cools, and there will be characteristic deposits and alteration products.

Much of the "water" on Mars will be locked up as permafrost in km-thick icefields, in the pores between the rock grains and in cracks and fissures in the shattered impact-pulverised bedrock.

Whither White Mars?

Well, I think there may no longer be a "need" for liquid CO2, but there is still an "option" for it. If there is no liquid CO2 in the subsurface of Mars, then we have a lot of "missing" CO2 to account for. Maybe there are deep subsurface carbonates that have consumed it - maybe this happened way back during the formation of the planet and the carbonate is buried in churned-up impact debris.

I think my models of springtime avalanches are still viable.

In short, I've stepped back from asserting that there never was any liquid water on Mars - The evidence in support of water is irrefutable.

I do, however, argue that liquid water may only have had a minor role in shaping the planet's surface, desite a few spectacular exceptions.