How Much Water Will A Human Colony on Moon or Mars Need

[@elephantwalkersmith1533]

Nuclear Chemical engineer here. The type of nuclear reactor mentioned by the professor would not require water on the moon for cooling. Uranium nitride or similar fuel at an enrichment of 20% would create a core about the size of a trash can, and could be cooled by molten salt. Water would not be required. See LANL for a reference on this reactor.

[@spaceherpies]

And you think there are salt deposits on the moon??

[@elephantwalkersmith1533]

No, but the amount of salt is on the order of kg’s , not tons.

[@ericsmith6394]

Is there a working molten salt cooled reactor on Earth? This idea has been around for decades. I don't follow news on this but I had the impression no working model has ever been made. Research reactors maybe?

[@STSWB5SG1FAN]

@@ericsmith6394 In the early days they were experimenting with both molten salt and pressurized light water reactor tech. There were some promising results with the molten salt designs, but for >reasons< it was never followed up on.

[@Spherical_Cow]

​@@STSWB5SG1FAN like for instance, those >reasons< included chronic problems with extreme corrosion (due to those pesky molten salts), that resisted all efforts to resolve...

[@cmayor7985]

Aquaponics (fish aquaculture + hydroponics) is more water-conservative than soil agriculture. You also get two crops for the price of one, and scrub some CO2 out of the air. It will be a staple of future space-food systems.

[@bernhardjordan9200]

Unless you vent water to vacuum or put it back on the ground I don't understand how any water would be really consumed

[@Veramocor]

@@bernhardjordan9200 well some of the water would be incorporated into the biomass (starches cellulose) as hydrogen. To recover the water from the cellulose you would have to burn the cellulose and then condense the water. You’d also lose water by transpiration but that should be recoverable by simple HVAC dehumificatuon.

[@damfadd]

Acre feet is the dumbest conversion of any imperial measurement ever known to man

[@attilajuhasz2526]

Correct.

[@staticgrass]

Especially when you then start talking about drinking water usage in liters.

[@jameslmathieson]

Spacecraft designer weighing in: The heat drill thing makes no sense to me. All you need to do is to scoop up the "water ore" and place it into a sealed container. You then move that container into the sunlight. The sunlight warms the container and the water sublimates, pressurizing the container with water vapor. If more heat is required, use mirrors to concentrate more sunlight on the container. You then release that water vapor into a pressurized distillation tower in the shade to liquify it (maybe requires a pump, depending on vapor pressure achieved). Now you have perfectly clean distilled water, no reactor required. You dump the dehydrated regolith out of your container and go get a new load. Required systems: 1 rover with a front loader scoop 1 or more pressurizable dump trailers 1 distilation tower (or pump + radiator) 1 water tank Some pipes and maybe a dry (non-oil) vacuum pump Optional plus up: Concentrate a lot of sunlight onto the container to smelt the regolith for metals, extracting water just as the first step. Probably better to have your pressurized crucible be a stationary facility in that case rather than movable pressurized containers.

[@BabyMakR]

Agreed. You're going to vaporise the regolith and end up with water saturated with minerals and solid rock that you then need to crush to extract the materials from it. Take it and put it in the sun > water evaporates (essentially distilled) > put the still powdered regolith into the refineries to extract the aluminium and titanium and whatever else from it.

[@Miata822]

James, yes, this makes a lot of sense. I seldom watch these colonization videos or read the comments. So many of the energy-intensive activities they discuss are powered electrically by hand-waving "and then magic happens." Using solar thermal energy directly seems obvious to me, especially for processing local materials. Rejecting heat from your condenser will require some engineering, but won't require magical thinking.

[@IOSARBX]

Fraser Cain, Subscribed because your content is fantastic!

[@nicholashylton6857]

Excellent talk! It's always great to hear a well thought out argument about the challenges of living on the Moon and possibly Mars.

[@waynecottrell6238]

Great interview! Could've listened to you two for hours

[@ThanosSustainable]

Mixing sq. meters and liters with acres and feet was definitely a brain torture. Get your units together.

[@DanielVerberne]

Annoys me greatly. I'm Australian and absolutely gobsmacked that Imperial measurements still have users.

[@doncarlodivargas5497]

Wasn't it a space rocket disappearing into the universe or something because some scientists mixed SI units and imperial units some years ago?

[@BartJBols]

@@doncarlodivargas5497 no, it crashed on mars. Several actually.

[@doncarlodivargas5497]

@@BartJBols - ah, OK, but still not a good idea to mix IS and imperial

[@snozzmcberry2366]

In his credit, as soon as Cain brought up metric, he started mentioning the metric equivalents as well.

[@BitcoinMeister]

"there are people right now on the moon" May that be a common saying VERY SOON! Great positive message to end the show with!

[@Fiercefighter2]

Thanks for putting this together! It was a really nice watch with my breakfast and I learned something new.

[@mobileroto]

Superb interview! Thank you!

[@Hyrum_Critchlow]

Really enjoyed this interview!

[@billcade2137]

Thanks Dr. Jeffrey, your topic was very educational, and appreciated.

[@TheReferrer72]

The Moon is a harsh mistress!

[@tonytaskforce3465]

It's hard to love her well.

[@acmelka]

Full episodes of Space 1999 are available on KZbin. We actually thought we'd have a moom base by now for sure. Not the space leisure suits and alien hippies though

[@ewaf88]

Maya would have to be dissuaded from turning into a sea sponge

[@X5493-c7p]

The moonbase in UFO was better and that opinion has nothing to do with the purple wigs and silver mini skirts ;-)

[@ewaf88]

@@X5493-c7p And I deliberately turned my eyes away when Lt Gay Ellis started to change.

[@ilkoderez601]

Great talk! Definitely enjoyed it!

[@ComputerGarageLLC]

Q: couldnt we just --- whats the word -- sublimate? the water from the regolith? Dig it up, run it through a enclosured conveyer in the sun to make the ice to sublimate to gas, then pull the water vapor out of the enclosure? Im sure you would still have to purify it, but that would be less energy intensive. Just a thought.

[@czerskip]

How about we just stick to cube meters? 🤦‍♂️

[@nicholashylton6857]

I prefer cubits or furlongs^3, personally. Much easier to work out the sums.

[@falconne]

"I use 40 rods of water per hogshead and that's how I likes it!" -- American probably

[@michaelstoliker971]

Because you need 1233 of them to equal 1 Acre-Foot some SI units of measure are just unwieldy and arbitrary.

[@SebastianSchleussner]

Or bananas? 🤷‍♂

[@falconne]

​@@michaelstoliker971 The guy in the video was saying "about 486,000 acre-feet" which is 0.6 cubic kilometres which is not at all unwieldly. SI uses factors of 1000 between units so it's easy to deal with arbitrarily large or small numbers. It's Imperial that deals with unwieldly numbers, since it requires knowledge of numerous conversion factors and fractions to go between arbitrary medieval units, so you end up sticking with units like feet or gallons even for large numbers.

[@lukeskywalker7457]

Good timing with this story. I live in Calgary AB, and we have 3 water mains that are broken as of yesterday.

[@elephantwalkersmith1533]

The inventor of this reactor used a stirring cycle with a compressed gas and a radiative cooler

[@sgramstrup]

What does 'Acre-feet' translate to in normal Scientific language ??

[@PatrickOCnMD]

Getting to Mars and just getting back safely would be a great 1st step. I am almost 72, and I just do not think I will be able to see it in my lifetime. But I can certainly hope, however.

[@danaen803]

Among the many problems, Arcadia Planitia Glacier is up to 1km deep where SpaceX has most of it's primary and secondary locations, there are also the large glaciers under Medusa Fosse Formation at the Equator. No pipelines from the poles are needed.

[@saxonsoldier67]

Can we at least get enough trips to the poles in order to have a series called Martian Ice Road Truckers ?

[@DanielVerberne]

Can we PLEASE all use the metric system if it's not too much to ask?!

[@ekothesilent9456]

America is about as far away from using metric as Texas is from New York. 5 school busses, 650 football fields and 220,000 Big Macs side by side. 😎 murica.

[@robertkooiman27]

Acre feet! 1st time I hear that! My metric mind doesn't compute...

[@warpeace8891]

We are part of an interdependent biosystem. I have heard little from any source about trying to survive apart from Earth in this aspect. A future guest on this topic would we worth my attention.

[@jlmwatchman]

One of the first things Jeff said was that we won’t be eating Burgers on the Moon. My first thought was, ‘What about the Mealworm Burgers with Mushroom Bacon?’ I listened to the podcast by Erika Nesvold that discus issues about space habitats we don't like to hear. Making New Worlds by Erika who is a Ph.D. astrophysicist and a lifelong space travel enthusiast.

[@okkomp]

Acre-feet? Why not measure it in football field-bigmacs.. It would make more sense.. Thanks for at least asking but the correct unit is m3 ;) hectare-m = 100,000m3

[@okkomp]

I spoke too soon, football field reference. Finish your drink

[@spacechannelfiver]

@@okkomp it should be in olympic swimming pools, everyone knows that

[@damfadd]

@@okkomp brilliant

[@Srfingfreak]

It's crazy the esoteric insight you're able to elucidate.

[@chriskelly6574]

Well I hope they include a few Eagles for Moonbase Alpha!

[@jimmyjames5960]

1 acre foot is 1233.48 cubic metres

[@B0tch0]

Which is 325,851 gallon in eagle units. An astronaut on the ISS uses about 1 gallon per day (less than 4 liters) and it remains very recyclable. If you ever lived in the desert with no access to water for several weeks, 1.5 gallon is enough for drinking, cooking and washing. So, on the moon, that would be enough for 1000 people for a year WITHOUT much recycling, and assuming food is imported dehydrated.

[@unvergebeneid]

Thank you! I was starting to silently sob over how American a unit acre feet is. Cubic feet would've been just as useless to me but at least it wouldn't have broken my soul.

[@Robbadobbsoldier]

Yeah a scientist using acres….. not very scientisty. Let religious Americans measure in barrels and acres and all the smart people can use meters and kilos.

[@4of20]

@@Robbadobbsoldier how do you stay cool in the summer?

[@Robbadobbsoldier]

@@4of20 I’m always cool 😎

[@saumyacow4435]

The Professor is quite correct. Agriculture would require a lot of water. So much so that it would be simpler to export food from Earth, rather than shipping to the moon all the materials and equipment needed for mining, extraction, energy production and so on. I'm glad he said it "the megawatt range".. that's a lot of mass all exported to the moon.

[@CityOfTinyLines]

Frasier I was amazed by the footage of Starship reentry. Curious as to what the cameras are actually like and wondering if you could do a few minutes on it?

[@Raz.C]

Chemist here. It seems like a chemist would be the person to speak to about extracting water from hydrous or even anhydrous minerals that might be found on the moon.

[@gelisob]

29:40 Question: why go straight to pipelines, here on earth we also move natural gas for example in big ships, how difficult is it to have large airships on mars to move water from caps to equator base?

[@2150dalek]

Great discussion. Indeed Space1999 was different. Cmdr Koenig was more worried about sustaining resources and maintaining a functioning moon base whereas Capt Kirk directly if not recklessly explored space to meet aliens.

[@marshalleubanks2454]

Here is a way to think of lunar water : It amounts to what you would get from taking one inch off of all of Lake Erie - i.e., a Lake Erie inch as opposed to a 486,000 acre feet.

[@dougm3037]

Great interview. The moon is the obvious way station for exploration of deep space IMO.

[@genuinefreewilly5706]

I remember Space 1999 well. It was problematic in that they just happened to pass by a planet almost every episode outside the solar system. Christopher Lee as Captain Zantor was pretty cool Some interesting ideas: so moon base alpha happens to go into orbit around a planet where the earth moon turns naturally habitable, for whatever reason in the script that becomes a bad thing.....

[@STSWB5SG1FAN]

If I remember the story correctly, the aliens on that planet made the moon habitable to keep the Moon base Alpha people from going down to their planet and trying to colonize.

[@marklewus5468]

“Don’t drink the water! Not one drop.” - Doctor Who, The Waters of Mars

[@oldtimer2662]

water, water everywhere and not a drop to drink… Samuel Taylor Coleridge 'The Rime of the Ancient Mariner'

[@terminusest5902]

It is likely much of the water is very salty. Liquid salt can act as a coolant fluid in some situations. Fuel will likely be a huge requirement. Underground water is likely available in large quantities. Distillation is a relatively simple separation method. Possibly with solar power. China is operating 2 MSR fission reactors in the Gobi Desert using molten salt for coolant and heat transfer. Agricultural use in a sealed environment should be very efficient. Underground bases could be very effective. Moon regolith bricks are likely to be effective construction material. And even solar cells. Once established operating costs should come down relatively low.

[@NicholasNerios]

Agreed find the water before committing to a base. But just because it's a lower quantity of water doesn't mean give up, there's fueling, mining, refining, space maintenance, science and medical research, logistics, most of the operations could be ai, or possibly just a spendy weekend lunar resort for the wealthy.

[@Miata822]

Anyone interested in what it would take to run an off-planet base should look at the closest thing we have to that on earth, the Amundsen-Scott South Pole Station. KZbinr 'Joe spins the globe' has overwintered there as a maintenance tech and has made a series of videos that you should see for a reality check. Especially check out the two part tour of the station. Sure, conditions at earth's south pole are different, but just take note of everything that uses energy and where that energy comes from.

[@zapfanzapfan]

I hope there is a nearby glacier wherever on Mars we decide is interesting enough to put up a base. I imagine we would like to explore somewhere similar to where Curiosity and Perseverance is, a crater that housed a lake and has lots of sediment to dig/drill through.

[@danaen803]

Most of the SpaceX primary and secondary sites are on Arcadia Planitia Glacier with 2m regolith, 10m mix of regolith/ice then a pure water glacier up to 1km deep. Honeybee Robotics (Kris Zacny) has the REDWATER system that can operate at 1T/day. The numbers used in the paper addressed are using household numbers for 100gal/person day, NASA estimates are 3.53kg/person day. He does not consider the technology available to NASA/SpaceX for Habitation Systems - ECLSS

[@LesNewell]

60% water recovery from agriculture seems very low to me. 50-60% at the farm seems realistic but a lot of the water in the produce is going to be released again when we cook and eat it.

[@alangarland8571]

It would be handy to find a Carbon source on the Moon. That means that the Hydrogen created as a byproduct of creating Oxygen from water can be converted to methane, which is more energy dense than hydrogen as a fuel. It also is much easy to store than Hydrogen.

[@iancudmore9795]

Long term Luna can't be both populated and provide fuel. I think when we consider the volume of water that Dr Lee suggested we need to support humans there that the amount of fuel expected for moon bases to provide will start as fairly low and reduce overtime

[@FernandoNuevo-il7ym]

I’ve wondered about using the regolith on the moon and mars for filtering water

[@JamesCairney]

This was good

[@BeauDadda]

Saw a thing a few days ago about using green polarized light at a 45 degree angle it will cut the bonds between the water molecules causing evaporating (faster than just applying heat or all spectrum light.), so a movable tent like set up maybe grow room work in combination with the drill room?

[@BeauDadda]

Couldn't link it but it's out of MIT it's called photo molecular evaporation of you wanna look it up

[@faolitaruna]

25:10 BTW, I still see models of the Eagle Transporter in various places.

[@POLICECAMERA6688]

Explore the Moon, with a focus on the South Pole where there is a large amount of water. The water here does not exist as a pool but is mixed with the Moon's regolith layer, requiring technology to exploit. Water extraction requires thermal drills and a steam collection system. Using solar energy is feasible, but careful consideration is needed, such as not using a nuclear furnace because it requires cooling water. However, we also need to be aware of the challenges of establishing a fully self-sustaining base without Earth; This may not be possible in the near future. Compared to Mars, the Moon has the advantage of distance but still faces the challenge of small meteorite impacts.

[@saxonsoldier67]

The long term health risks from low G should be substantially less both on Mars and Luna as frequent surface excursions in full gear will probably double the mass of each individual.

[@marknovak6498]

R&D water extraction and use couple recycling is a decades long project for the moon.

[@saumyacow4435]

Fun fact: Humans synthesise water through metabolic activity (the hydrogen comes from carbohydrates). So on a realistic "moon base" where food is transported from Earth, water is actually created by the humans. Given a sufficiently efficient recycling system, we do not need to extract water from the environment. Indeed the energy production and mining and materials processing and chemical engineering involved would require so much mass that it would be self defeating. it would make more sense to simply import food. And on top of this we will have methane and oxygen for propellant in large quantities and that can also be converted to water for human needs. We're talking realistic bases - a few dozen individuals. Not colonies (which serve no purpose).

[@ericsmith6394]

What if we placed a dome but instead of landed solar we used a mirror in orbit to make it hot? Solar is an inefficient step if all you want is heat. The heat can also be used for electricity and at night.

[@marksinclair701]

Fascinating stuff. One question, I thought there were lower latitude craters on Mars that have water. Like Korolev maybe? Or do they still get long periods of darkness?

[@jamiedoe6822]

What about the frozen water underground on Mars at the equator?

[@jamesdubben3687]

Excited to see tesults applied to earth.

[@kezz55]

Recycle the water from our bodies is more than enough to keep us hydrated if done created very carefully for us to filter than to the mouth 🤔🤔☺️❤️😀👍

[@LuisFernandoForeroGuzman]

Is it possible to generate energy using water temperature change in the moon or other places in space. Meaning moving water in a pipe from hot places to cool places in a cicle?

[@ericsmith6394]

Yes, you can get electricity from almost any heat gradient. I don't know how much in this case. It sounds like something that is difficult and risky. If a rock hits your solar panel you might not even lose the whole panel. Hit a water pipe, though...

[@BabyMakR]

Check out RTG Stirling engines.

[@ericthatcher]

Have there been any experiments on the vomit comet to simulate Moon's gravity or Mars's gravity?

[@zapfanzapfan]

The tourist flights usually have a few parabolas of Mars gravity and a few of Lunar gravity.

[@ilkoderez601]

I think Mars compared to rotating habitats is crazy. Rotating habitats with lunar and asteroid resources is the way to go.

[@iancudmore9795]

Long term , probably. I think we see test settlements on Mars and Luna until that extra engineering is sorted out. And I think that gives enough of a foothold getting those two places that a population is maintained there, which expands over time.

[@JeroenvanGutsem-u7e]

Newly discovered photomolocular effect/ photo evaporation might offer a new avenue of exptracting water from moon ice regolith slush.

[@MistSoalar]

Scientists like Dr. Lee make projects actually happen.

[@frasercain]

At least the math part, anyway.

[@bernhardjordan9200]

In a close system how he proposes less than 100% water reclamation?

[@iancudmore9795]

Yeah a reactor that uses plutonium for fission and treats water as disposable is a bit silly on the moon. But that's obvious isn't it? Thorium salt reactors seem like a far better solution there, especially considering the surface thorium deposits

[@AliHSyed]

There’s no doubt that Mars poses challenges that Moon does not but from the perspective of self-sufficiency, a Mars base long term would be far more successful than one on the simply because of the abundance of resources.

[@monolalia]

People on the moon? That’s crazy talk!

[@tylienmusic2269]

Great

[@brandonspirito]

Can we "suck" up water with a heated vacuumed tarp on the moon?

[@Thetimecapsuletx]

Do we know if the moon has any kind of water table?

[@TagiukGold]

That's unknown, but not likely.

[@abrahamroloff8671]

Totally unknown, but it's not impossible that there could be relatively large pockets of ice "near" the surface. As in; Within a couple km. Also not impossible for there to be actual liquid water, under pressure, way down deep if the core is still warm enough.

[@Mr.E-gi5rq]

Enough to terraform it.

[@TerryCooperYT]

I just hope to live long enough to see a moonbase established. And Elon has hinted that he wants to call it Moonbase Alpha, which is a no brainer.

[@Madash023]

A pipeline a quarter the circumference of Mars seems way too insurmountable of a challenge to construct in such an austere environment. Why wouldn't you just regularly deliver water from an automated polar mine to the base via sub-orbital hops, using water as fuel? That seems like a way more feasible solution to the problem, and way easier to execute with the resources on hand already. Not sure why a pipeline is the first thought.

[@iamsuzerain3987]

I'm thinking that in the beginning of our Lunar aspirations there will need to be a lot more robots than humans operating on the Moon. If we can somehow establish ourselves beneath the surface it will be far safer and feasible. Perhaps machines engineer a cavity beneath the surface where humans can exist in small numbers (perhaps 3-5) early on and we slowly build upon this spartan infrastructure. I believe that eventually we will succeed in establishing a sustainable human presence there but by no stretch of the imagination will this be easily accomplished

[@kezz55]

A lot a hell of a lot of water+food oxygen and physical parts for moonies to put together 🤷🤩🤔🔥🔥🔥👆👆👆👆👆👆👆👆🔥🔥👌👌👌👍❤️☺️😀

[@philhooper4196]

Instead of using a probe or drill, which will lead to mechanical failure, I have an even better idea: use a high-powered microwave beam to superheat the water. Microwaves can penetrate several feet of regolith.

[@czerskip]

We like guests who did the math. Now we only need a few more who confirm said math over and over again until we correct our predictions with reality when the time comes ;)

[@itsmodsiw]

Fritz Zwicky presented models in the 60s ;)

[@JeroenvanGutsem-u7e]

I believe we should fly in a 5 year supply of protein powder/vitamines/creatine and a legpress with 3000 kg load capacity to accomadate for the lower gravity. sure beats building large farms and associated water needs.

[@JeroenvanGutsem-u7e]

instead focus on a selfreplicating gigafactory initially for robots, mining and solarpanels, once suffient robotforces have been created build all that needy stuff for human colonizers to offer them a turn key solution

[@andrewrobinson9497]

i noticed in independence day resurgence they were walking on the moon like they were walking on earth this would be true

[@marklewus5468]

I get the point your guest was trying to make, but three days with a blown up tooth that needs a root canal can be a very, very, very long time.

[@GadZookz]

If I ever go to Mars then Fraser Cain and Isaac Arthur are coming with me.

[@sinukus]

What would it be like on the moon during a meteor shower like the ones that happen every year, would it be survivable?

[@executivesteps]

You would never know it’s going on. The individual shower particles are separated by hundreds of miles (and more).

[@brentgilbert6613]

I was 9 years old when the first moon landing. I remember wondering if it was real. I still don't know if I believe it or not. It's odd that they don't have the technology to go back now. But I want to believe.

[@LesNewell]

"we need lots of electricity to melt water." A few minutes later.. "we can't use nuclear to generate electricity because we cannot remove the heat." Umm... wait a minute, does anyone else spot the obvious solution here?

[@doncarlodivargas5497]

They can't melt ice because they don't have heat, and they can't produce electricity because they don't have water, humans plans to colonise the universe will never be realised

[@mattkeith530]

I hope there is a lot of water because it's not replacing itself

[@BabyMakR]

Hydrogen and oxygen are both found in lunar regolith and both would be released as part of refining the regolith.

[@LubosMedovarsky]

Square meters of slar panels and acre-feet of water in one talk, how cute🙂

[@marvinmauldin4361]

The time frame in which we make a Moon base depends on the escalation of the space race with China, Japan, et al. The driving force won't be science, but global power politics.

[@StefenTower]

Sometimes I wonder if we're being too clever when we already know how to send tanks of Earth water to the Moon today. Sure, using Moon water is a good long-term or backup solution, but our main solution? Just send water.

[@StefenTower]

On top of this, we can extract water back out of waste water via osmosis processes, likely simple to set up on the Moon.

[@philhooper4196]

Instead of extracting by digging, why can they just create a giant heat probe that can be inserted into the ground and collect the steam that comes from the ground via moveable dome, and once the pressure has built up, then siphon or vacuum into a heated storage container

[@philhooper4196]

right after I say this, he goes on and tells me my idea

[@philhooper4196]

I need to get paid

[@beefandbarley]

Hired. Please report to Lunar Base Alpha.

[@philhooper4196]

@@beefandbarley I just hope it didn't take them to spend millions of dollars for what took me 30 seconds to devise

[@mbj__]

Pls ask future guests/ scientists to use only metric when discussing tech topics. Wild mixing causes confusion.

[@tarumph]

Fortunately, the perpetually lit parts of the moon are close to the perpetually shaded parts of the moon. :)

[@viperswhip]

Water is not the most valuable resource in space it is probably one of the most common compounds in space, the only problem is logistics.

[@realmstupid-on8df]

I love it how we still just trash earth like she's our main girlfriend while we go treat out side girl better.

[@acanuck1679]

An iInteresting interview. It was a bit distracting to hear Dr Lee use non-SI measurements. Best to use litres, metres and hectares. It's less confusing. As for the old "Moon versus Mars" argument, I'm not sure that his claim (that Mars is far and therefore much more difficult) "holds water". Where he sees problems (in the existence of a thin atmosphere), other credible experts have seen great potential. Furthermore, the water resources to be found on Mars would almost certainly be much, much more copious than what would be found on the Moon. But, sure, some settlement of the Moon would likely be interesting--if it were economically viable (and the very low gravity did not pose serious problems for procreation and long-term habitations).

[@hamjudo]

If only 60% of water used in lunar agriculture is recoverable, someone is doing something horribly wrong. The farm is going to be part of a sealed environment. Water "lost" to evaporation is recovered by the process that manages humidity. Plant waste will get composted. The plants that get eaten will just lead to water in human waste. Biology will do some chemistry with the water to use the hydrogen and oxygen in other compounds and vice versa. As long as the vast majority of biological waste goes into a compost pile, the microbes will do their thing to make sure that the hydrogen and oxygen aren't permanently lost. A tiny colony may capture organic gases in carbon filters so it won't poison the colonists, but not actually go to the effort of recycling them. So methane produced by decay could actually escape from the system. A larger colony would produce enough volatile organic compounds that it would be worthwhile to recycle them.

[@marknovak6498]

The energy needs would be required at lot solar cells or a nuclear reactor.

[@Preciouspink]

Does the moons of Mars have water?