update: Water at the poles has some more recent news:
- Science: 03-August-2018 Radar evidence of subglacial liquid water on Mars
- EarthSky.org: 28-Sept-2018 Pink lagoon provides clues to possible Mars life
- Space.com: 25-July-2018 Mars' South Pole May Hide a Large Underground Lake
- Science News: 18-August-2010 Mars (probably) has a lake of liquid water
I just wrote a comment that includes the following sentence:
I think the J. P. Morgan of Mars will get rich shipping water from the ice near the poles to the people near the equator where it's sunny.
But I was being whimsical and not thinking it through.
While there is oxygen everywhere in the atmosphere (in the form of CO2) water for drinking and growing food (carbohydrates!) and for hydrogen for fuel (and perhaps other uses) on Mars might really need to come from water ice near the poles.
If regolith near the poles is say 20x more hydrated than near the equator where it's "warm and sunny" (also important for growing food), is there any even remotely, potentially economical way to move the water from the poles to the people?
Canali? Pipes? Trains? Hydrogen balloons? ATVs? Anything?
"Economical" I suppose would mean that it takes 20x times less excavation and processing resources per kg of water, but more resources to move it to where it's needed. Even more because it may be nonlinearly more difficult to extract any water from nearly dry 2% rock than from a nice juicy vein or layer of polar ice.
below: Here's an upload to Wikimedia; click for full size.