As you pointed out, 18 atomic weight of H2O is lighter than normal air and therefore all water would rise away from the planet surface to the upper atmosphere, just as all light elements and molecules do.

Also when splitting H402 water molecules with electrolysis, we get 2(H2) on one side and 2O on the other.

H2O at 18 would seem to be lighter than N2 at 28 and O2 at 32,

On earth, low pressures are caused by air with lower temperatures, with the most common cause being a storm with a large amount of water mass and humidity. (water when frozen expands becoming lighter or fluffier… when heated, it expands many times it’s normal size becoming buoyant enough to float next to our stratosphere, despite being 4 hydrogen atoms heavier then normal air)
As water vapor expands becoming fluffy taking up more space, heavier nitrogen and oxygen must move out of the way resulting in a drop in air pressure and temperature. This void creates a vacuum resulting in wind which always blows towards the negative air pressure. Wind friction, because it takes energy to force air to move, results in higher air temperatures of a few degrees. Upon reaching the low air pressure, the wind cools and condenses creating more vacuum. Eventually the storm vortex breaks up and spreads out.

This makes me wonder if the near surface water they detected in this area is creating the circumstances for a low pressure event? I’m not going to presume what works on Mars is like earth… especially since CO2 is closer in atomic weight with H402.
I also do not see vortex movement associated with these dust storms, not a cyclone as associated with storms on earth.
But then Mars does not have magnetic field. On earth the storms have a PH (natural acid rain) that induces current, sometimes lightning, which drives the storm to move circular inside of a strong magnetic field.
The closest to a vortex is UV charged dust creating dust devils.

I remember a wet soccer field where but a single lightning strike felled many players.

Brines a similar threat?

Consider fluidics, Elon.

And all optical computing as back up.

No touch screens.

You have a 1950’s rocket. I want to see 1950’s switches and nixie tubes. NORAD stuff.