[Robert_Paulson2]

so then, WHERE is the water.
If it was liquid, where are the theories about WHERE it has gone or WHY it has changed?

liquid water needs 32 degrees to thaw.
when was the last time Mars saw 32 degrees?

If it was two billion years ago, or two weeks agon makes a difference. We have suspected WHAT was on mars, for a long time. WHERE it is, went or how it left matters a lot. What we can do to recover and use it, matters a lot.

very frustrating...
we KNOW mars had water... is it on the north or south poles or what?

[Rebel_Ace]

"...liquid water needs 32 degrees to thaw. when was the last time Mars saw 32 degrees?..."

Actually, in very low pressure environments, solid ice "evaporates" directly into the air without going through the "liquid" phase. When this is happening, the term (or verb) for it is "sublime", as in the ice sublimed into vapor. Since the air pressure on Mars is so very low, I would expect a chunk of ice anywhere away from the extremely cold poles to slowly disappear on it's own.

Once the water vapor was in the air, hard radiation could split the Hydrogen and Oxygen, where the lighter Hydrogen could "leak away" into space, and the heavier oxygen could bind with material on the surface to form a crusty-rust.

[jpthomas]

A high salt (NaCl) content can depress water's freezing point by as much as 23 °C. Thus, in addition to the known water vapor in the Martian atmosphere, and the water ice at the poles, there could be water ice and liquid brine just below the Martian surface, as well as deeper aquifers.

[green iguana]

"when was the last time Mars saw 32 degrees?"

Probably yesterday. Daytime highs on the red planet average
in the low-mid 40's. Just doesn't stay there very long, and
gets much, much colder at night.