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Let us suppose a world that exists under a harsh red sun. The entire planet, which may once have been fertile, is, in its current state, covered with desert. The civilization living there, which may have once been more technologically advanced, has the technology of the Iron Age.

On this desert world, water is a valuable commodity. In addition to drilling for it out of deep wells, it might be possible to recover what little water is evaporated in the air, perhaps with a device like this?

enter image description here

How does this thing work anyways?

How would you build a moisture vaporator with Ancient technology?

The device must operate, freestanding, in a desert, with no nearby ocean. It must be able to condense water out of the air and run it down into some sort of underground cistern for storage. To be clear, a fog fence won't work in the middle of a continental desert.

For the conditions in the desert, use any conditions that you can find in the Sahara, at least 100 km from the ocean. So, mountain ranges and oasis are to be expected and fine to take advantage of.

While I prefer an Iron Age feel, you can use any pre-industrial revolution technology necessary to make the device work.

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    $\begingroup$ Air well. Atmospheric water generator. P.S. The device in the picture is way too small; it doesn't matter how it works, it can only extract water from the amount air it intercepts; and it doesn't intercept that much air at all. $\endgroup$ – AlexP Nov 18 '18 at 23:04
  • $\begingroup$ How much are you looking for, if you built something the size of large building it might generate a mouthful , but it will collect dust much faster than water. There simply isn't much water in the air to collect. $\endgroup$ – John Nov 18 '18 at 23:25
  • $\begingroup$ It would be way more practical to use that work to pump water. Air is dry in deserts so it is hard to get water, more over a decent amount. $\endgroup$ – Artemijs Danilovs Nov 18 '18 at 23:55
  • $\begingroup$ What the average humidity of your desert, for most of the really dry deserts your are talking about only a fraction of a percentage humidity available for harvest. $\endgroup$ – John Nov 19 '18 at 0:00
  • $\begingroup$ @John Conditions of the desert edited into the question. $\endgroup$ – kingledion Nov 19 '18 at 0:02
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The essential idea behind a saltwater greenhouse would work. Instead of seawater, use urine and feces. The greenhouse traps heat and moisture inside, allowing for crops to be raised. Put a condenser on the other side from the toilets. That will produce clean water from the humidity. The toilets provide the moisture. It will of course stink in the greenhouse, but the water less so. It may absorb some of the smell from the air, but the water vapor is just water vapor. If there's too much smell, distill it again with a second greenhouse.

The Romans had greenhouses:

According to Pliny the Elder, Roman Greenhouses “consisted of beds mounted on wheels which they moved out into the sun and then on wintry days withdrew under the cover of frames, glazed with transparent stone or mica.”

It's not that hard to make glass either. An advanced society that fell back to an iron age level of technology might retain glassmaking. The secret to glass is lots of heat, applied to sand, limestone, soda ash, and broken glass. Your people might scavenge glass from the ancient cities to help make new glass.

A water seer (as mentioned here and here) could be added to produce additional water to offset sweat losses.

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    $\begingroup$ @kingledion If you collect all the urine and feces, you get most of the water people produce. But people also sweat. So over time, the toilet greenhouses would recycle less than 100% of the water even if they were perfect. My main point is that they couldn't recycle 100% of the water unless people lived in them. They need to be supplemented from other sources, e.g. oases, cacti, wells, other tech. And while there are critical posts in that forum thread, there are also supportive ones. $\endgroup$ – Brythan Nov 19 '18 at 4:24
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You say the world is all desert but there must be some vegetation or the food chain won't work.

Cultivate cacti and other plants that are already capable of extracting moisture from the air. Harvest them and suck the moisture out of them. The same with root vegetables. Australian aborigines traditionally are very good at finding such roots.

Condensing water is the other method.

You have iron so a condenser is no problem. Use it at night when the air is coolest.

Combustion of any hydrocarbon (such as is found in dead vegetation) produces water vapour.

Urine can be distilled to produce pure water.

In the iron age with wood, pottery and iron you could make a water seer.

enter image description here

Note that the Iron Age Romans made quite complicated machines and civil engineering.

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  • $\begingroup$ Well im going to vote for this because it is as right as the OP is gonna get even though the OP claimed fog fences wont work, which cacti basically are. $\endgroup$ – anon Nov 19 '18 at 13:41
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    $\begingroup$ I'm amused by the use of an image of a scam project that only exists to milk the gullible out of kickstarter money. $\endgroup$ – pluckedkiwi Nov 19 '18 at 15:28
  • $\begingroup$ It will work only if close enough to coast. As Soil in hot places is hot too, so you need more humidity to make it work , even if you make better engeneering, not just scam-project. $\endgroup$ – Artemijs Danilovs Nov 19 '18 at 23:02
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Walls with holes in, lined with the shells of Desert Beetles.

As the wind blows through the holes, the Beetle shells capture tiny amounts of water, until each droplet reaches 5mm in size and rolls off the shell and down the inside of the wall.

(Warning: You will need a lot of Beetles, or a way to create an artificial surface with alternating hydrophobic and hydrophilic materials.)

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