Most astronauts, before we new of this sickness, had a hard time getting reintroduced to Earths gravity. But now we know what can cure the sickness. The exercise does. It helps the body stay toned for the return to Earth. Exercise and gravity are probably the most important thing of the entire history of space flights, and will continue to be in the years to come following our colonization of Mars.
Water is hard to obtain on the dry surface of Mars, but it can be done.
We developed a system for water retrieval at the Nasa space building. You see the retrieve water and use it. Then the water becomes a vapor and relies from the plant. The water becomes a solid once again and falls into a container of some sort. Then it is as pure as the water that is described in the waste section.