How to supply water to a coastal desert town with no rain and no freshwater aquifers?

Question

Think Tatooine in climate, but with oceans. Here are a few restrictions due to setting:

• There is modern technology, but not too much electricity ie no super high amperage machines.
• Population is small at first (only a couple hundred), but is growing since this town has a strong supply of water and other towns do not.
• There must be enough water for drinking, showering, and small amounts of farming. Fishing is the primary food source.
• The people are mostly very poor and shipping the water is not feasible except for the wealthiest members of the village (one of the themes here is the conflict this brings)
• The solution should be buildable by people without lots of money

Any suggestions re desalination, condensation, etc are welcome.

Answer 1

It's a coastal city with lots of sunshine in a modern setting. You have everything you need and more. All you have to do is desalinate the water and it's done. Took less than a minute research.

OK, you have to scale it a little better than in the link.

Channel the seawater to shallow fields, coated with water resistant foil to prevent seeping it to the ground. It should be a few cm water in each field. Transparent vinyl (or what it's called) close above it. It lets through the sunlight, speeding up the water evaporation. The vinyl catches the evaporated water droplets and with a slight tilt, they will flow to a prepared storage (or the agricultural fields). The salt remains, which they have to collect, but they can sell it for good money.

The amount of water is only dependent on the size of the fields.

Answer 2

Qanats.

https://whc.unesco.org/en/list/1506

https://en.wikipedia.org/wiki/Qanat

A qanat or kariz is a gently sloping underground channel to transport water from an aquifer or water well to surface for irrigation and drinking, acting as an underground aqueduct. This is an old system of water supply from a deep well with a series of vertical access shafts. The qanats still create a reliable supply of water for human settlements and irrigation in hot, arid, and semi-arid climates, but the value of this system is directly related to the quality, volume, and regularity of the water flow. Traditionally qanats are built by a group of skilled laborers, muqannīs, with hand labor. The profession historically paid well and was typically handed down from father to son. According to most sources, the qanat technology was developed in ancient Iran by the Persian people sometime in the early 1st millennium BC...

Qanats are super duper cool. They are ancient engineering marvels which still do what they are supposed to do millennia later. These underground aqueducts move water from distant sources (often miles away!) to arid lands and offer a bunch of side benefits - in addition to clean water, qanats can provide cool air. Read on how having a qanat pass under your house offers cool air pulled up thru the house via a chimney.

Answer 3

An extreme possibility, which requires some suspension of belief: This town lives in a small plain surrounded by mountains. Local winds bring heavy fog 24/7 which is trapped in large collector/condensers.

Answer 4

September 2019 update briefing: it turns out that desalination is becoming more scalable by the day. This kind of changes the answer depending on the fine tuning of the restrictions set.

Actual solutions used in the coast of the Atacama desert:

• Fog collection. The wind from the sea does bring some water, which you can collect, but it's limited, not very scalable.

  Older Update: limitations of fog collection include the maximum water content of fog (saturation) and fog collector efficiency (which depends on wind speed). Also, according to the OAS: Their water supply can still be contaminated by windborne dust, birds, and insects. The moisture collected can promote growth of mold and other possibly toxic microorganisms on the mesh.

  As a rule-of-thumb reference, this paper states that in optimal conditions a fog collector can theoretically collect 75%-95% of the water content of air at wind speeds between 2 and 8 m/s. Unfortunately these conditions worsen with bigger size of the collector. Assuming the best throughput takes place at top speed AND with a decent content of water in air (usually ranging in the grams/cubic meter, say 10), you get a few dozen grams of water per sqare meter of collector per second ($8\times10\times.95=76\,g$), but can optimal conditions be sustained all day, all days? Typical throughput in the Atacama desert (I assume desert=dry, Atacama being one of the driest, though) is around $5\,lt$ per square meter of collector per day.

• Desalination of seawater is still expensive, not very scalable. You can lower standards (taste, purity) to get a little more water, which could fuel your conflicts. Military sea vessels get water through desalination, using a combo of temperature, osmosis and pressure (thanks to their engines).

  Update 2 (September): it seems that technology is advancing faster than I was aware. According to this news outlet (in Spanish, linked to the Chilean branch of the Turner group—CNN), Antofagasta would have 100% desalinated water supply by 2020. Antofagasta is a 300,000+ inhabitants coastal city in the middle of the Atacama desert, whose main economic activity is related to mining (mainly copper.) Caveat: the article does not cite any sources, and its wording is ambiguous: It first says that current supply covers 80% of the demand in the neighborhoods served, by Aguas Antofagasta (the local supplier,) which might mean not the whole city. See here for an article by Aguas Antofagasta about their current collection process, including desalination (also in Spanish.)

  Regarding the amount of electricity demanded by the process, there is little information given by these sources: they say 1) water is pumped from $400\,m$ from the coast, $20\,m$ below sea level (this requires energy, not necessarily electric,) and 2) water is desalinated through inverse osmosis; this is probably sped up by increased pressure (which also requires energy.) Anyway, the fact that its currently being scaled for tens or hundreds of thousands of people, means it probably satisfies most of your concerns.

  The main question now would be why other cities don't have the same supply of water. It could be that the local economic activity is what makes water desalination economically feasible.

Other:

• Pipes from oases.
• Underground streams.
• Water trucks.

All in all, technology from a few years ago, would limit your settlement's population, unless you can bring water with pipes or something else, but it's becoming less of a problem today.

FWIW, when I was a kid, cities in the Atacama desert relied on external sources, and needed to ration water.

Answer 5

@Lupus just reminded me that I should pay a LOT more attention to other answers! His answer is this answer and it was posted before mine. Please go upvote his answer! It's a good answer! Thanks!

Behold! A time-tested method for desalinating water

Wiki how shows us a modern method similar to that I used as a teen in the Scouts. (Image from Wiki How.)

The process is simple: evaporate the salt water and let it condense on plastic, then drain the plastic someplace useful.

Here is a video showing how to do it with some plastic bottles found on the beach.

Here is a video showing a larger operation.

This system can be easily scaled so long as you can support whatever material is being used to condense the water. Honestly, it's conceivable you could do this over whole acres, letting in seawater through a gate and draining into a cistern.

Answer 6

Assuming your oceans are salt water, these are a few ideas that occurred to me:

Use wide-bandgap semiconductors to perform photo-electrolysis -- separating the hydrogen and oxygen using photons ( 2 photons + 2 H2O -> 2 H2 + O2 ). This is a technical possibility today, the development to make it engineering solution is still in progress. Then, ignite the gases and you have pure H2O again.

Evaporators: The village has dug channels for water at high tide to fill wide shallow ponds enclosed in plastic tarping. The heat of the sun evaporates the water, leaving the salt behind, then water is condensed in shaded metal tubes that act as heat exchangers -- looks like large stills

Orthographic lifting + modified natural caves + passive heat exchangers:

The village sits on a wide peninsula surrounded by mountains that funnel the air higher and higher to a canyon or pass at the top. The mountains are honeycombed with natural caves, that people extended using explosives so they open on the other side of the mountains.
The moist winds are cooled as they rise -- a consequence of orthographic lifting -- and air going into the caves is cooled further. The water condenses in underground reservoirs. This all only works because of the strange and unique geography and limestone or sandstone mountains in this area.

Answer 7

Make water from coal.

I proposed this to Innocentive as a way soldiers could make water for themselves in arid climates: condense it from vehicle exhaust. The cleaner your carbon source (natural gas would be ideal for this) the fewer contaminants will be in the water you will make.

Assumptions:

1: This is a planet with an oxygen environment.

2: There are hydrocarbons like coal available to be burned.

The formula for oxidation (burning) hydrocarbon is CH4 + O2 -> CO2 + H2O https://energyeducation.ca/encyclopedia/Hydrocarbon_combustion

The big fluffy white plumes one sees coming from the smokestacks of coal plants are mostly water steam, produced as the product of combustion.

Some napkin numbers: considering a pure carbon hydrocarbon (more like coal than natural gas) you get 2 moles of water from every mole carbon burned. That means 1 ton of coal can be burned to produce 226 liters of water. A human needs to drink about 2 liters of water daily.

You would definitely want Israeli-style water conserving agriculture in a situation like this. You would need a readily available carbon source like coal or oil to burn. You would need a way to condense the steam and then possibly distill it again to remove contaminants from your hydrocarbon source. As regards distilling you fortunately have a heat source you are not using for anything else: all the burning coal.

Answer 8

Aqueducts

Aqueducts have been used for thousands of years to get water from one place to another. No modern tech needed nor materials but it would help speed up construction.

The Roman Aqueducts were up to 57 miles long and some are still in use today. They can be built of stone or timber.

The OP states this town has good water but other do not which means it has to have something others don't have. Desalination and/or condensation plants can be built at any town and in fact the other town would build their own

Answer 9

If this is set in the near future, desalination plants should be an option.

The main requirement is lots of electricity. They have lots of sunlight. At present the capital cost of solar PV panels may be prohibitive for a poor community, but this is because of the nature of Silicon solar cells. We already have perovskite solar cells working in the labs. The goal is a solar panel that can be manufactured almost as easily as spraying paint onto glass. So set the story in a future where that goal is realized, and where solar panels are as cheap as glass windows. That in turn will drive the cost of the rest of the desalination technology way down.

As per other answers, you can do low-tech desalination with just plastic sheeting, and sell salt as a bonus. But agriculture is thirsty. I rather doubt you can desalinate enough water for subsistence agriculture that way. Perhaps they only need vegetables as dietary supplements, and get the majority of their calorific intake as fish/ seafood? (If you relax the "no aquifer" constraint, you can have deep-rooted crops such as grape vines, which can pull up water from very many feet underground. Perhaps a low-permeability aquifer, which is not useful if you dig a well into it, but which such plants can use).

Answer 10

As others have mentioned fog/moisture capture and transport from other regions, but perhaps something to compliment... how to maximize the impact of what water you do have.

The design of spaces and usage of plants to create micro-climate effects to maximize water impact. Consideration of succulent type plants for pioneering/climate modification.

So, regarding plants/micro-climate. If you've produced an enclosed space and have grown trees these are beneficial because you moderate the exposure to the sun. If you look at that image of the qanat, this is indicative, the trees shade the ground and water, minimizing the evaporation of what is there. The more shade you have, the more you conserve what water you do have.

https://forestsnews.cifor.org/10316/make-it-rain-planting-forests-to-help-drought-stricken-regions?fnl=en https://en.wikipedia.org/wiki/Desert_greening

Furthermore, the trees will buffer wind, and can themselves capture a bit of moisture in the air, and of course slow down evaporation. On a larger scale, trees actually help to produce rain, as they do breathe off water themselves.

Consider this, if there is moisture in the air, but not enough to rain... as this moisture passes over a forest, where trees are breathing off moisture, the combined effect of the ambient air moisture + tree breathed moisture, combines to produce enough total moisture to cause precipitation (enough water combined will fall as rain).

So downwind somewhere you'd probably want to consider capture and some sort of piping/aqueduct, like the qanats. And send that moisture back to your cultivated forests upwind. This could be an expanding system that, although fragile, could be something that would slowly scale.

More trees would shelter more land/water, and breathe more moisture, which would interact with the evaporated moisture from the sea, which could precipitate, leading to more water to pipe back to said trees, which could be expanded to shelter/breathe more moisture, interacting with more sea moisture, etc.etc.etc...

Anyhow, regarding succulents. There are various species of plants, like cactus, and these are of course species most adapted to low moisture levels. https://en.wikipedia.org/wiki/Succulent_plant

These could be interesting considering a systematic approach to the landscape/microclimate and if you used the tree/shade/moisture model, could be used as a notion of "pioneering" species. So before you plant trees, you have cacti and other succulents, helping to intercept moisture/attract animals and shade the ground.

Every bit of shade/water interception counts in this model.

On top of that, if you consider what "agriculture" means, there are succulents that are used in that regard. Consider agave: https://en.wikipedia.org/wiki/Agave

Agave can produce food, and of course is used in tequila production.

Furthermore, there are plant species that are highly salt tolerant. These could utilize some of the untreated water. They would again be able to provide shade/animal habitat, and would themselves contribute into the water feedback loop described above. https://www.gardeningknowhow.com/special/seaside/gardening-salt-water-soil.htm

Considering the availability of salty water, these salt tolerant plants + succulents could help form the "outer boundary" and pioneer the land, helping prepare for a slow adaptation of regular trees/plants to enter the space as water is available to irrigate.

So, in total, this is a multi-dimensional approach to the usage/protection and increase in moisture, rain production, capture, and forming a slowly scaling feedback loop to promote more and more rain production/interception and water presence in desert greening type of way.

If you combine this sort of "perma-culture" approach with the technological captures/transport described by others, you could have a more holistic approach to water production/capture/conservation.

Hopefully that is inspiring, and not just in your fiction, but also for real life.

Answer 11

(Edited)

Well, even if there is almost no rain, there still may exist some rain. People can dig large holes or build containers in which they store water from rainy periods and use it along the year. Some people make that in semi-desert areas in Brazil, however the water is not enough for luxuries such as baths and in your case would need some complement.

Also, it's possible for the desert to have underground water sources that can be accessed via wells. These sources are basically like "underground rivers" that are born in far away areas where the soil absorbs more water.

One other thing that I could think is the use of plants. Desert plants are good at retaining water, so maybe you could have a special plant that can get water from very lower levels in the soil and be used as a water source. I don't know, though, how much of these plants would be needed to supply a person and if it would be enough.

The other option is desalinization. People are saying it's viable and kinda easy, but as far as I know, it's usually costly and used when nothing else works; a last resource. However, if your society really depends on it, they may have worked a way to make it cheaper and easier.

Many of this options can change according to other aspects of your geography, of course, like mountain ranges and hidden underground water sources.

Answer 12

If the city is located close to the sea, the winds blowing from the sea inland will carry some humidity.

Overnight the falling temperatures can lead to the humidity condensing, therefore a series of drapes oriented parallel to the wind direction can act as condensing surface, letting then the water flow into channels to a reservoir.

Answer 13

I’m going to challenge you on the shipping water. Oil costs \$0.5-0.75 per barrel per 1000 miles via pipe, \$4.25-5.50 per barrel per 1000 miles via train, and \$1 per barrel per 1000 miles via boat to ship. An oil barrel is 42 gallons. This gives us a price of \$0.01-0.13 a gallon of oil per 1000 miles. If water costs the same as oil because it is shipped from other countries, this would mean water would cost the same price to be shipped, plus an additional cost of basically nothing for water. Now, if you are willing for people to act like we do, people could be using 100 gallons of water a day. This would cost a citizen about \$1-13 a day per 1000 miles, which is considerably high, but manageable for everyone. This leads to a question of how to weed out other towns. A simple method is to have your town have a good military or good strategy to protect the water shipments. Water shipments are much more valuable than oil and would of course be targeted by enemies. A big side effect of military control of the water is that important people have control of the water supply, so perhaps your wealthy individuals control this (or do whatever would happen to create planned conflict) and they continue to have good water.

Answer 14

Presence of coastal cave systems

If your desert is set on a plateau and that the coast is very high compared to the water level, then the water could had eroded the rock and created the cave system. Such cave system would channel wind underground and condense the air moisture from the sea into underground pool.

The local population could have then carved the rock and created part of an underground city (think Mesolithic underground cities as seen in middle east). The speedy, moist winds would also provide cooling and air that would be less harsh compared to that of the desert. It would be very like Dune sietchs with their wind trap, except that it would be much more successful on the sea shore.

[EDIT typo]

Answer 15

There could be springs of fresh water just off the shore. This would create pools of brackish water off the shore that would be pottable.

I am struggling to remember the details of something I read but somewhere in Polinesia or another series of islands it was discovered that there were such just off shore pools. They were identified as in use by anchent cultures as both inland catchment basins constructed by digging pits for rainwater or land springs and some beaches had similar carvings facing the pottable water. Until someone tested that salinity of the off shore water they could not explain what the carvings that marked drinkable water were facing the sea. Turns out the underground rivers were exiting at known locations and the fresh water was not well mixed with the sea water when it reached the surface. If you new where to go in your little boat you could get barrels full of slightly salts but healthy to drink water.

Your city could be on that lucky bit of the coast. Row a few meters off shore to the right spots and you can fill your boots so to speak. This could be the only location on the coast with such a resource which then explains how this city has a suffit but no others do (as anyone on any coast can desalinate and will pinch the idea and tech before long).

Answer 16

A double-purpose greenhouse-desalinator is a good idea. Think of using greenhouses with evaporative cooling system. However, the only source of water is from the sea. The water is not directly used for irrigation. It is used for creating a cooler and humid environment. The air outlet is humid and is a source of water by condensation.

Advantages: Low-tech (Relatively), uses less energy, serves for two purposes without excessive energy consumption.

Note that the desert is very similar in its climatic system to the ones in the Arabian peninsula area, from the east gulf to the red sea. There are no rising thermals which cause rain and the air is dry. This means the evaporative coolers will work very efficiently if you need a much cooler greenhouse for crops.