Calculations show liquid water can exist at isolated locations on Mars.
Scientists have done simulations of temperature and pressure ranges on Mars and found locations where water could remain liquid during daytime Summer hours. These temperature and pressure ranges are even greater when it is briny water.
For a start see here:
Making a Splash on Mars
On a planet that's colder than Antarctica and where water boils at ten degrees above freezing, how could liquid water ever exist? Scientists say a dash of salt might help.
http://science.nasa.gov/headlines/y2000/ast29jun_1m.htm
Perhaps if you could explain your calculations?
Bob Clark