hi CD, why should a planet like Mars not have water? even though Mars is half that of Earth, all the evidence so far shows that free flowing water did exist at least once in the planets evolution. water and water ice is evident in other places within our solar system. take Europa one of the main moons of the planet Jupiter and at about minus 230C the whole moon is one big ocean covered with a three or four mile crust of ice, and Europa is half the size of Mars. water ice has been found on our moon and most of Saturn's ring system are small bodies covered in water ice.

the real question should be where did all the water come from in the first place.