Background: I am a writer for a newsletter that reports on space exploration, with a particular focus on colonization of other planets.  I am presently working on a series of articles on the colonization of Mars from the perspective of "living off the land."
Request: I need a report about what is known about the presence of water ice on Mars that could be used to produce drinkable water. This includes both information about where the ice is, how it might be mined, and what kinds of processing would be needed to make it drinkable.  Because my focus for this article will be on drinkable water I am interested only in water ice, and not in other forms of ice such as salt water. I need to explain to our readers how we know that this ice actually exists, so I am interested in both what evidence we have for its presence and how confident we are in our interpretation of that evidence.