Its becoming increasingly evident that Mars was once possessed large oceans. The image below, courtesy of Nasa, shows the McLaughlin crater and evidence that it was once filled with water. Composite minerals at the bottom of the crater show that it was once filled with water, possibly fed from ground water.
Its possible that the Freman up there have vast stores of water, kept in secret underground reservoirs . . . .
Wait I think I got Dune confused with Mars . . . . Nasa for more.