Water ice has been detected in the permanent cap at Mars' north pole, and may exist in the cap at the south pole. But much water is probably trapped under the surface - either as ice or, if near a heat source, possibly in liquid form well below the surface. read more
It has frozen water there, which would make it more likely to sustain life. read more
In 2004, NASA landed two robot rovers called Spirit and Opportunity on Mars. These rovers investigated rocks and soil and took pictures of features that seem to prove Mars was very wet in the past. Water already has been found on Mars in the form of ice in the polar ice caps. read more