So let's suppose for a minute that we have the task of proving that there is water available on Mars now, even in the face of NASA's staunch denials.  Can we prove that there is water using their own data?  Can we prove it even ignoring the frozen seas, glaciers, frost, ice crystals in the dunes, and the underground reservoirs found by the ESA?  Yes.

Minerals can be water resources

NASA has already analyzed and published the composition of the soil, its salts, and the minerals in some areas.  This is more than enough information to prove that even without the ice and water reserves, we can still obtain more than enough water from Mars for permanent colonies and even industries.  Here is how.

First, let's look at what Steven Squyres, principle investigator had to say about salts and water on Mars (article here).  You will note that he states that water, probably acidic water, came from underground and deposited salts (in particular sulfate salts) in the soil.  Meridiani Planum and Gusev Crater have both been surveyed and tested well enough to know that in some areas, the salt content of the soil can be as high as 50%.  The salts in question are mostly iron sulfate (or melanterite) and magnesium sulfate (or Epsom salts).  Because of their composition, both of these salts contain large amounts of water, but in a dry, crystallized state.  The water is literally a part of the molecular structure of the salt and helps give it the crystal structure it has.  Experiments show that as long as the relative humidity is high, even in near vacuum, the salts can retain their water.  This is good news because on Mars, the relative humidity is extremely high- nearly 100% most of the time.  (Articles on Mars relative humidity here and here.)

Also, the sedimentary rocks located in Meridiani Planum are composed primarily of gypsum, which is calcium sulfate and also contains water as a part of its structure.  The soil itself is mostly silica sand and iron oxides but contains gypsum dust mixed liberally into it and large amounts of the salts mentioned above.  So just how much water can we get from a stone?

I have assembled three specific cases to show that water is plentiful- first case, a collection of the salts only, second case, a collection of mixed salts, soil, and stone, and third case, the stone only.  Using the chemistry returned by MER and acknowledged by NASA and JPL, I can prove that with little more than a sealed oven and heat source, any explorer on Mars could refine as much pure liquid water as needed.

What do the numbers look like?

If we look at the salts only, and consider the largest components as a simplest case, we would have a mixture of half and half magnesium sulfate and iron sulfate.  By their chemical formulas, they are 51% and 45% water, respectively.  Let's see what a cubic meter of this material would yield if we placed it in an oven and heated it until the water emerged as vapor.

First, a cubic meter of this material would mass about 1161 kilograms.  It would give us over half a cubic meter of water- 556 liters of water to be precise.  The image below puts this into perspective.

Heating a cubic meter of the salts present in the Martian soil would yield about 556 liters of pure water

Now, let's consider a mixture.  The salts can be as much as half the soil, and if we literally used a front end loader to pick up a mixture of the Meridiani gypsum rock and the soil, we would get a pretty realistic view of what a large-scale production operation might be.  For my numbers, I have assumed half the volume is gypsum rock, and the remainder is soil- half salts and half sand and dust.  Here is the yield.

A cubic meter consisting of half rock, one quarter salts, and one quarter sand would yield 477 liters on water on average

Even this effort is going to produce a very useful amount of water.  In other words, there is no need to be picky- the material you load all contains some water and all can be released simply by heating it.  Now, what if we restricted our operation to rock only?  After all, gypsum is about 21% water by mass, so just how much water can we get from a stone?

Even with nothing but the sedimentary rocks (which are gypsum), we get a lot of water

Amazingly, even this strategy yields a huge amount of water.  Two cubic meters of Meridiani sedimentary rock could yield over a thousand liters of water.  The yield  is almost 308 gallons.  And remember, we have not called on geysers or groundwater, frost, glaciers, or underground ice.  I have used nothing more than those resources that NASA itself admits are present today, and have the chemical data to prove.  So even if NASA was correct and Mars did happen to be drier than any desert on Earth, there would still be no realistic limit to the amount of water that an explorer could obtain on the planet.

Now, what do the experts say about this idea?  Here is an article in PDF format showing how sulfate salts store water and how much water is present.  This news article details some of the findings and their implications.  Astrobio articles here and here show the same- that unknown to most people, there are immense stores of water on Mars just in the minerals and salts!  Nature magazine also supports this view in this article and the list grows even longer now as researchers find that gypsum is a plentiful rock on Mars and is loaded with water as well.

NASA is still slow to accept or broadcast the news, but they have admitted that water played a key role in the creation of the rocks and structures seen on Mars in this press release.

What about the ice?

As it stands, ESA is far more forthcoming about the ice resources of the planet.  Even in the face of direct images of water flow today, NASA continues to deny the existence of liquid water on Mars.  But Malin Space Science Systems shows where water eruptions have been recorded before they evaporate away, causing dust slides (as they call them) on valley and crater walls.  This image is very clear and shows what I believe is liquid water in action on Mars today.  Underground ice can account for this very easily.  Here is an excerpt of the image showing strange dark streaks and flows.

I believe that these streaks represent an eruption of liquid water to the surface.  Note that this is consistent for the following reason- older flows would evaporate away, becoming more faint.  They would also be more "spread out" as they wet the surrounding soil.  This is exactly what appears to be shown.  But also take notice of one other significant thing- the source of each streak is a tiny point- consistent with an eruption from a single point.  A single, gushing source of underground water could create each of these streaks, and then exhaust itself.  All the flows run downhill, and all show signs of spreading out and evaporating.  Water is the only answer- it is available in the atmosphere, so we know that it can easily evaporate from these sources and account for the high humidity on Mars.

New results from MSSS show liquid water pooling on the surface

In this image, MSSS says that "seepage and pooling" can explain what is seen.  They have other thoughts about what it might be but do admit that liquid water is a possibility.  The presence of islands in this material and the flow patterns under the surface are good indicators that we might be imaging a seasonal flow of water into a crater lake on Mars.  The original image can be seen here at MSSS.

Note the dark pool of material with islands in it- and also see the edges of the crater where it is apparent that some liquid has flowed downhill into the lake below.  In my opinion, this is a clear example of groundwater, whether from ice or other sources, flowing downhill and forming a pool in the bottom of this crater.

But wait- what about that sulfuric acid?

Remember what Steven Squyres said about sulfuric acid from underground water creating all the salts in the first place?  It seems that NASA has overlooked one very significant fact about sulfuric acid- to form, it requires free oxygen and liquid water!  Once more, a piece of evidence has been either ignored or gone unrecognized and it is a very important one- it points to free oxygen in Mars' past, as well as liquid water.  Is there more evidence of past free oxygen on Mars?  Yes!

The color of the planet itself is due to iron oxide- rusted iron!  The only way this could happen is if plenty of free oxygen was present, as well as liquid water.  And after all, the same process occurred on Earth leading up to the Cambrian Explosion, when life diversified and became the dominant force on Earth.  With all these signs, how can anyone deny that Mars was, and likely still is, a living world?