The Moon has some water. Maybe quite a bit. Perhaps a lot less salty than Mars’. Which also makes it a good source of materials overall for a space habitat. Much cheaper to get stuff from the Moon than from Earth.
And remember: recycling can be quite efficient. Look at the various space stations.
The problem is distance which adds time.
“The fabric of space we say.”
Origami Instructions - Instructions on How to Make Origami ← This is what we need to learn more about.
Think about it.
That new way to fold “T” shirts… Just scale up… 
If humans would dedicate a iittle bit of effort toward sociological advances, instead of depending on technology as the solution to every problem, the planet we’ve got would be plenty good enough. We’re talking about technologically conquering outer space, while still clinging to 2,000 year old societal dogma.
What really irks me about the push to go to Mars is the apparent “been there, done that” attitude to the Moon, as if we learned and did all that we possibly could in six missions that put 12 men on the surface for a total of 15 days, 45 years ago.
The Moon is only two or three days away. Mars is six months, FFS! It might be possible in a Moon exploration program to have a rescue ship kept on standby just in case, but once the Mars ship takes off, they’re on their own, no matter what. They could all die before they even get there, and there’d be nothing the rest of us could do but watch.
But my main objection isn’t the risk to human life. I’m okay if a bunch of people want to commit suicide on a crazy trip. I expect and hope that Congress would never approve any significant amount of U.S. tax money for this, and I don’t suppose I have any grounds to object to a billionaire throwing his money away if he wants to. So it’s not the money.
It’s that it’s STUPID! Why not learn how to live and work on another world using the one that is practically next door, only 240,000 miles away, instead of hundreds of millions of miles? Going to Mars will be vastly more expensive, vastly more difficult, vastly more dangerous, and vastly more likely to fail, and fail catastrophically, than trying to do the same thing on the Moon.
It’s like deciding you’re going to learn to scuba dive, and instead of taking classes at the local YMCA pool, descending to the Marianas Trench (but not for 20 minutes). It’s nuts!
It doesn’t have to be 6 months to get to Mars. Elon Musk’s idea is to get there in about 3 months. And that’s probably the only way we’ll get there without a ship that generates pseudogravity by spinning. And having enough shielding to block out most radiation. (See the links Stranger provided on the dangers of extended space travel.)
But from what I can tell, Musk’s idea is to fuel (and his ship requires lots of fuel) from the ground. I don’t think that’s going to work unless we can bring launch costs down even further than his ships will. We’ll have to find some way to generate fuel in orbit, maybe from a captured comet or something.
And both of those requires precise planetary alignment. So to go there and back requires waiting for an alignment to occur again. (As well as needing the SF-level tech to be developed in the latter case.)
If there’s an emergency and something needs to be sent to/from Mars stat, lotsa luck.
The Moon barely needs any alignment at all. Almost all of the launch window stuff from the Apollo days was needed to ensure that the chosen landing spot was lit just right.
But, again, going to the Moon isn’t sexy. Elon Musk thinks there’s no glory in going back there. And glory is a bad justification.
Material and energy is literally worthless if you must expend a greater amount of material and energy to get it. You are literally suggesting the equivalent of spending $20 in gas to drive a couple hundred miles to pick up a quarter.
If we’re going to send humans to Mars, let’s be absolutely clear on the benefits of that:
That’s it. There aren’t any others. Mars is cool, and seeing a person standing on Mars would be insanely cool. I would skip my own wedding to watch that live. But it’s a dead planet and a ridiculous place to try to “colonize.” The negatives are
I’m not saying we should or should not do it, but we should be honest about why we’re doing it.
Good Blog post here by Charles Stross about - Mars expeditions aside. How useful a spin off a ‘Big dumb booster’ capable of doing the job would be.
http://www.antipope.org/charlie/blog-static/2016/09/what-else-can-you-do-with-a-bi.html