[calex59]

While a Mars colony sounds nice, as does a moon colony, where will the water come from? Yep, you can grow vegetation inside a dome for the oxygen, and food, but you need water to do that, you also have to have some for the humans to drink.

All this may seem obvious but I have yet to see anyone explain where this water will come from. Ice on Mars, I am sure, but how much and how difficult to get to it?

[WhiskeyX]

The water comes from the soil. Even if the soil does not contain significant amounts of water ice, the planet has an immense quantity of carbon dioxide in the atmosphere which would be combined with the hyrogen in the rock to produce water.

If the prospect of using such chemical means to produce large amounts of water is deemed to be too impractical, it would not be unreasonable to redirect the orbital path of a comet or water rich asteroid to impact on Mars and thereby resupply Mars with seas of water.