It has ice at both poles. But not much. There is enough to over Mars to at least 11 meters. That might sound a lot, but it is small compared with the amount of ice in Antarctica. There is probably a lot of ice elsewhere underground. The higher latitudes also have large areas of permafrost with ice close to the surface.

In equatorial regions however the ground is dry to a great depth. Far drier than our deserts. Yes Curiosity found a surprising amount of water bound in the sand (NASA - NASA Mars Rover Fully Analyzes First Soil Samples ) - but it was surprising for Mars only - similar quantities to the water bound in the sands of the Sahara desert - it is still very very dry.

The water boiled off at 835 degrees C. Curiosity Rover Makes Big Water Discovery in Mars Dirt, a 'Wow Moment' It's a high water content compared to the very dry moon, but not compared to Earth. And the water is bound and not available for life to use. Even dry granite is often 3% water content r/askscience

The distribution of the changes over geological timescales, because Mars's inclination keeps changing (so also does its orbit - sometimes more elliptical, as it is now, at other times more circular). At times its ice caps are probably more extensive. At other times its axis tilts so far it has equatorial ice sheets.

There is probably water deep inside Mars, what they call the hydrosphere, kilometers below the surface where the temperatures rise above the melting point of ice, and trapped by the rocky layers above.

Then - there is a fair bit of moisture in the atmosphere, which at night causes frosts, even in the equatorial regions.

But you can't have liquid water on Mars for any length of time at present. Over most of the surface the boiling point is below its melting point because the air is so thin. In a few places at the bottom of the Hellas basin for instance, there is enough pressure so that the water is just below its boiling point of a few degrees centigrade, but any patches of water would still dry out pretty quickly.

All the same there are some possibilities for small amounts of liquid water. These can be

• Droplets of water on interfaces between ice and "salts" (on Mars these are generally sulfates, chlorates and perchlorates rather than the chlorides and sulfides we have on Earth)
• Water trapped under ice and melted by the solid state greenhouse effect
• The mysterious "warm seasonal flows" - amongst all the dark streaks on Mars, these ones have no explanation yet except as possibly some phenomenon caused in some way by seeps of liquid water.

Also if you get a large meteorite impact, especially at the poles, this can cause a lake to form. If the impact is large enough, the lake is still liquid after it gets covered with ice, and the insulating effect of that can keep it liquid for up to a thousand years or more. So from time to time Mars even has extensive patches of water on the surface covered with a layer of ice, at least - theoretically that should happen.

Also it is not yet completely geologically dead - is good evidence that it has had eruptions in the recent geological past though none active right now. So you can also get ice that's melted by geothermal heating - and if trapped underground may be able to remain liquid.

But - Mars has far less water or ice than we'd expect. There is evidence of an ancient ocean that may have covered much of the Northern hemisphere. If that's true, then it's an interesting question, what happened to all that water? Did it sink underground perhaps? Or did it get dissociated into hydrogen and oxygen with the hydrogen lost to space? Or a bit of both or some other explanation? Nobody knows. Hopefully we will find out more soon.

See also my:

Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,...