I think this also derives naturally from another really interesting observation. The surface of Mars, that apparent desert, is 2%+ water by weight. [1] I say "+" because later studies have shown it to be even moister. So this is really interesting in the context of the movie/book "The Martian" because this surprise came out after the book was released.

A huge part of the plot is about him getting water which he ultimately does by extracting it from fuel, but it'd have been trivial to get it from the soil itself. If you can excuse the butchery of measurements, even just the 2% level is moist enough to extract a liter of water per cubic foot of soil! For more consistent measurements, that's 35 liters of water per cubic meter of soil!

I suspect when we finally get boots on the ground and can start doing real research and exploration, we're going to find more surprises than we could ever imagine.

[1] - https://www.space.com/22949-mars-water-discovery-curiosity-r...

We may have to decontaminate the water, which might be full of azides or other things. On the flip side those compounds may be useful for industry or fertilizer in the long term.