Just to add to the other answers here - it depends on the depth of the water and also the surface you pour it over. A thin patch such as might condense out of the atmosphere will just freeze or vaporize. In the lower regions such as the Hellas basin, technically it is below boiling point - but even so - it is within just a few degrees of boiling point, and will evaporate quickly - just as your clothes dry in the sunshine - but more quickly.
If it lands on salt (much of the Northern plains consists of ancient salt pans) then the salt may take it up forming a salty brine with a lower boiling point as much as -20C or less, instead of freezing or vaporizing. The salts on Mars are perchlofates, chlorates and sulfates, while chlorides and sulfides are rare - but have a similar effect of lowering the melting point.
However, if the water has any depth at all, it will freeze over from the surface first. If the ice is clear, it will cause a solid state greenhouse effect - this creates layers of water in Antarctica a half meter or so below the surface of the ice.
This may show a similar process happening on Mars - these streaks are thought to be caused by liquid water, pure water (unusually for Mars) that spread out over the surface after first melting beneath a solid state greenhouse layer of pure ice. There are many streaks on Mars with different causes - only these particular ones are thought to be formed in this way.
If you pour the water in the equatorial regions - the desert sand there is dry to depths of at least hundreds of meters, so it will soak away into the sand without trace.
There is a rather surprising amount water in the Martian sand - but to put that into perspective, it is only surprising for Mars - the amounts are similar to the amount of water that is caught up in the dry Sahara sands.
The best place to pour it therefore is in the polar regions where there is ice already on the surface, or in sub polar regions where the ice is only a short way below the surface.
If you can pour out enough water to make a lake with a depth of some meters - then the surface will freeze over - but it will stay liquid below the surface for a surprising length of time.
After a major impact on Mars, in the polar regions, you may get subsurface ice covered lakes like this that last for a thousand years or more before they freeze solid.
Even at somewhat higher lattitudes, the impact could melt subsurface ice to form an ice covered lake at the bottom of the crater.
Perhaps would look something like this after the impact
but below the surface layer of ice it would be liquid water.
You could also get fractures with hot water in them, conditions a bit like hydrothermal vents soon after the impact, see "Water Warm Enough for Microbial Life Existed at Mars' Impact Craters" --New Research
For more about these impact crater lakes, see Lakes on Mars, especially page 91 onwards, where it discusses "heated lakes" covered in a thick layer of ice and kept warm either due to impact, for thousands of years afterwards - or due to volcanic / geothermal heating.
To find out more about other ways water can form on Mars today, Where To Search On Mars For Droplets, & Shallow Flows Of Liquid Water - Where Microbial Life May Flourish
If it lands on salt (much of the Northern plains consists of ancient salt pans) then the salt may take it up forming a salty brine with a lower boiling point as much as -20C or less, instead of freezing or vaporizing. The salts on Mars are perchlofates, chlorates and sulfates, while chlorides and sulfides are rare - but have a similar effect of lowering the melting point.
However, if the water has any depth at all, it will freeze over from the surface first. If the ice is clear, it will cause a solid state greenhouse effect - this creates layers of water in Antarctica a half meter or so below the surface of the ice.
If you pour the water in the equatorial regions - the desert sand there is dry to depths of at least hundreds of meters, so it will soak away into the sand without trace.
There is a rather surprising amount water in the Martian sand - but to put that into perspective, it is only surprising for Mars - the amounts are similar to the amount of water that is caught up in the dry Sahara sands.
The best place to pour it therefore is in the polar regions where there is ice already on the surface, or in sub polar regions where the ice is only a short way below the surface.
If you can pour out enough water to make a lake with a depth of some meters - then the surface will freeze over - but it will stay liquid below the surface for a surprising length of time.
After a major impact on Mars, in the polar regions, you may get subsurface ice covered lakes like this that last for a thousand years or more before they freeze solid.
Even at somewhat higher lattitudes, the impact could melt subsurface ice to form an ice covered lake at the bottom of the crater.
Perhaps would look something like this after the impact
but below the surface layer of ice it would be liquid water.
You could also get fractures with hot water in them, conditions a bit like hydrothermal vents soon after the impact, see "Water Warm Enough for Microbial Life Existed at Mars' Impact Craters" --New Research
For more about these impact crater lakes, see Lakes on Mars, especially page 91 onwards, where it discusses "heated lakes" covered in a thick layer of ice and kept warm either due to impact, for thousands of years afterwards - or due to volcanic / geothermal heating.
To find out more about other ways water can form on Mars today, Where To Search On Mars For Droplets, & Shallow Flows Of Liquid Water - Where Microbial Life May Flourish
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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