I guess the level of humidity will depend on the % of water they are able to recapture...I would like to know what technologies they plan on using to recapture the water..but this info might be a trade secret right now.
There are some interesting new techs that mimic nature's ability to condense water from moist air...using a mix of hydrophobic and hydrophilic materials, using no energy to do so. My bet is they are planning on using this stuff..could be arrayed like a web at the exits of the tunnels.
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