Harvester pulls 1.5 gallons of drinking water from arid air per day | Hacker News Reader

Harvester pulls 1.5 gallons of drinking water from arid air per day

newatlas.com

104 pointsBrajeshwar109 comments

Open articleView on HN

Full publication - https://pubs.acs.org/doi/10.1021/acsenergylett.4c01061

> 11.15–22.81 kWh/L

Are there any advantages over cooling condensation extractors? They seem to be in the 0.3-3.0 kWh/L range.

https://us.watergen.com/technology/

https://www.researchgate.net/figure/Liters-of-water-condensa...

https://www.ostfalia.de/cms/en/pws/turtur/solar-projects/con...

Sources of heat tend to be more available than sources of cold. You could theoretically marry the two, using the waste heat from the condenser to extract water.

> The potential downside is that this system requires energy to release the water – the base of the device needs to reach 184 °C

There are heat pumps that can go up to 200°C now, and if it’s already a hot environment I imagine they could be fairly efficient. The “cold” side could be connected to some black panels facing the sun.

But this would require a facility on an industrial scale so not something for a single home. Maybe a small village.

Is there a way to create a device a human can briefly power to reach that temperature? I imagine for much larger facilities there are much easier ways to get water than this.

sure, and there has been since the paleolithic, they teach how to make them in boy scouts

> Scaled up, that’s 5.8 L (1.5 gal) per kilogram (2.2 lb) of material used per day, which is enough to satisfy several people’s daily water needs.

No knock on the device itself but this is barely enough for two people, especially in arid conditions.

I think it's regarding daily drinking needs, and not other uses for water.

The metric I am familiar with is the average person should consume 8 cups of water a day, so 1.5gal of drinkable water would support that need.

> So how much fluid does the average, healthy adult living in a temperate climate need? The U.S. National Academies of Sciences, Engineering, and Medicine determined that an adequate daily fluid intake is:

> About 15.5 cups (3.7 liters) of fluids a day for men

> About 11.5 cups (2.7 liters) of fluids a day for women

> These recommendations cover fluids from water, other beverages and food. About 20% of daily fluid intake usually comes from food and the rest from drinks.

https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...

(Of course you can survive on less, but it's not ideal. A quick test to see if you're hydrated enough is to go pee. It should have the slightest tint of yellow to it. If it's clear you're drinking more than you need. source: first aid class I took)

The article doesn't say drink 11-15cups of water a day.

It says 20% comes from food, (which depends on what you eat, right?)

But taking it literally it would then say to drink;

12.4 cups for men. 9.2 for women.

Despite what common belief might indicate, coffee-soda-beer etc all count.

But yes, if you are self supporting you would need water to make those things at home so the problem doesn’t change much.

They count, just not ounce-for-ounce.

I know they count. I regret not changing what the article said to fluid in my post. The point I was trying to make is that there is a required / recommended fluid intake for people each day.

The numeric recommendation is "fluid" which includes water, food, and water included in other beverages.

It may seem like splitting hairs, but the OP's comment was regarding 1.5Gal of water not being enough for a single person. Using the 8-cups of water a day, 1.5gal of water does meet that requirement.

The 8 cups thing is pure tabloid science, like red wine is good for your hear, or getting 10k steps a day makes you more healthy. It's not actually based in facts.

I believe here it is used as a rough estimate of the drinking water needs of a human, and as such it is fine? The problem is when people take it as an exact number they must drink every day or else…

They also backpedaled and allowed that your first cup of coffee or tea in a day counts as one of those beverages. I think beyond that the diuretic effect cancels out some of the fluids.

If your pee is clear stop drinking. That’s how I rehydrate after a workout. That’s how a lot of actually healthy people do. Over time I’m growing more fond of the habit of calling people who aim for the trappings of a discipline without following it as cosplayers or LARPers. The people carrying the quart bottle of water are LARPing.

This seems weirdly hostile to drinking water. Some people like drinking throughout the day and/or feel better when they are well hydrated. Drinking enough water is one of the easiest healthy habits to pick up and stick with; it takes way less effort than exercising or learning to cook healthier meals.

> If your pee is clear stop drinking.

Why? A person has to drink a lot of water for it to be a problem, far more than someone out and about with a bottle is going to consume. More water probably won't help anything if your pee is already clear, but it won't hurt anything either and most people drink too little water as it is.

Getting mad a people for carrying a water bottle around just seems weird. Depending on the area, it's not always easy to get a drink any time you want one. I guess if people are bragging about how hydrated they are it would be annoying. Bragging about how healthy your habits are is douchey in any context, but I've literally never seen someone act like that because they drink enough water.

I read that the other way from the parent - in that you should keep drinking until your pee is clear. Then you're back to "normal" after a dehydrating event (the workout), so you can continue maintaining that level as normal.

And I agree that "constantly carrying the bottle" has become as much about the fashion as anything - there's a guy at work who always has a metal bottle on him, taking it everywhere. But they rarely use it - they've never refilled it at work, and less than 1l (I've never seen it less than half full, but assuming it is used over the day) over 1/3 of the day doesn't feel like theyre over hydrating.

most people don't drink too little water; you're reasoning from a false premise there

if you do develop this habit, your kidneys adapt by eliminating water faster. this is usually not dangerous in today's world, but it's inconvenient to need to carry around a water bottle and frequently find a bathroom. occasionally it can lead to mild dehydration if your access to water is interrupted for a few hours

also, inevitably, you do lose some salts with all that urine, which you have to replace, so drinking too much water mildly increases the risk of, in particular, hypomagnesemia (hypocalcemia and hypokalemia are much rarer, and you really have to be pounding the water bottle to get hyponatremia; on the plus side, you don't have to worry about being in acute hyponatremia for more than a few hours). these are a little more dangerous for the type of food faddist who believes things like 'drinking more water is good for you' because they're disproportionately likely to also believe that salt is bad for you

drinking extra water can be really dangerous for people with renal insufficiency, because they can get hyponatremia from fairly mild overdoses of water, but generally they're already aware of this problem if they have any access to proper health care at all

so basically it's an addictive habit with mild negative health consequences, similar to eating a low-fat diet, drinking coca-cola, or injecting heroin

under unusual conditions, like going to the black rock desert, continuing to drink when your pee is already clear is actually a good idea, because then you actually can get dehydrated without any urge to drink. but you should probably be drinking stuff with salt in it, like gatorade, though homemade oral rehydration solution is enormously cheaper

I think people get tired of being harassed about drinking water like you’re constantly in danger of falling over from dehydration. It’s not bad per se to drink more water than you need as it does help the kidneys flush the garbage out of your system. I think drinking when you’re thirsty and having meals is fine. Most food has a ton of water in it as well.

I don’t like being lectured to by people who think they’re the smart ones when their Illusion of Control problems are leaking out onto all of their friends and coworkers.

One of the sign posts of addictive behavior is when you allow your affectations to have negative consequences on the rest of your life.

better to over-hydrate than under-hydrate

Both can pretty easily do you serious harm if taken too far, up to and including death. Thankfully the survivable "buffer space" of "too far" is large enough that people generally pretty rarely ever get to the actual danger zone.

Here's one fairly famous(ish) example of over-hydration being fatal: https://www.nbcnews.com/id/wbna16614865

yeah, I'm familiar with that tragic story

but the reason for my previous post is because the upper limit for serious harm by over-hydration is quite high (it's difficult to drink that much water without urinating which was the key factor in that woman's death), whereas the lower limit for serious harm by under-hydration is not that low (not that difficult to hit)

so I would disagree that both can "easily" do harm

> so I would disagree that both can "easily" do harm

Easily enough but you're 100% correct that there's a fairly huge difference between the two extremes in how easy (or hard) they are to reach. Dehydrated to a dangerous point is most assuredly typically easier to achieve. Certainly easier by far to die from, too, as evidenced by how often the one happens compared to the other.

Studies have shown that less that 400mg of caffeine a day is fine for a healthy adult. Just watch drinks it after 4 or so unless you like it affecting your sleeping pattern.

In a dry climate it is very reasonable to calculate 2 liters of water (~8 cups) lost through respiration and perspiration. If this water isn't being replaced by food or drink, that's trouble. https://www.ncbi.nlm.nih.gov/books/NBK236237/

There was one study back in the 1940s(?) that justified it. The researchers who did the study intended it to include water that was in the food a person consumed but the person doing the press conference didn't know that and so responded incorrectly when some reporters asked him about that issue.

> tabloid science, like red wine is good for your heart

please don't burst my bubble

Many studies have shown that even 5000 steps a day can be associated with considerable better health outcomes than those who sit at a desk all day and work remote and get maybe 1000. Personally that’s my baseline and I take a walk like that every morning before I shower for the day. I do some mild strength training a few times a week and walk and that’s about it, and I can usually keep up with my homies when the occasional group hike or basketball game comes up. My doctor seems happy with my annual exams and bloodwork

My family uses about 20 liters a week per person. That's for drinking and cooking.

I suppose if I’m doing nothing, I’ll drink 8 cups in a day.

But most days when I’m out and about, I’m drinking about a gallon. And if it’s hot, it’s more.

There was a short and dumb period where I started buying plastic waste bottles and I was blowing through like 6-8 plastic bottles per day.

> I’m drinking about a gallon. And if it’s hot, it’s more.

Can I ask how tall / heavy are you? Gallon is almost 4 litres of water, I can hardly imagine anyone being able to drink more in a day, and even that sounds like a lot.

On hot days, I’ll drink nearly two gallons. Most days 1.5 gallons. Just water. I have a very large cup that is a pint and a cup. I’ll drink 8-10 of those a day. Though I eat a lot of salty/dry foods. America baby. If I go for a long bike ride I’ll be able to wring my shirt/sweatshirt and sweat will come pouring out.

After a long ride I’ll drink nearly half a gallon of water. Likely excessive but it tastes really good.

It’s likely there is a very large variation in the water people need to consume. During college, I knew individuals that would drink merely a glass or two all day (minus before/after going to the library). Very small water bottles. Though these individuals looked to be <100 lbs.

I think you’re talking to someone who is very serious about water consumption. Most people do not need a gallon a day. Not even close. While there is nothing wrong with it, we are not nearly as dehydrated a nation as the local news station seems to claim every 6 weeks or so or r/hydrohomies

6’ 165lbs

I remember drinking half of a 1 gallon plastic water jug in an hour changing a tire in the middle of a desert when it was 110°F.

If water were more scarce, you would adjust your activity to require less water.

The usual recommendation around here is to consume around 3l of water per day just to stay hydrated, i.e., not for hygiene or other uses.

Drinking water has to be higher quality than water used to shower or flush a toilet. In a place with only low quality water, this can be more efficient than purifying it.

Yeah that’s a crazy low number for several people. I think they are confused on the difference between the amount of water needed to keep several people barely alive vs able to function without concern.

When I was doing ag work in kansas during summer, I’d go through a gallon or more a day of just drinking water.

I am happy to see that we are ensuring the Fremen will have the technology they need to survive on Arrakis.

The spice must flow!

Of course, we are almost on the cusp of the Butlerian Jihad :)

If this is deployed at scale, I wonder how this would impact the plants and animals that depend on that water.

In absolutely no way whatsoever.

First of all, the proportion of water from the atmosphere would be absolutely minuscule.

But second, people drink the water and then breathe the moisture back into the air, or pee it and it winds up back in the water cycle.

I’m not saying one way or the other, but “minuscule” varies on the scale and just because there’s a closed loop cycle doesn’t mean there’s not a local impact to removing water from the area.

Local being your neighbors downwind.

> But second, people drink the water and then breathe the moisture back into the air, or pee it and it winds up back in the water cycle.

Not for nothing, but in really arid locations (like las vegas for example) human consumed water is fairly well captured. The water cycle ends up looking like a series of plumbing turning piss into potable water.

If your condensers drain into the sewer system, and its so hot outside that people are obliged to stay indoors… yeah for the part of the year where water matters the most I could see what you’re saying being true.

I'm glad my peeing into the wind is helping the circle of life

FTA: “The potential downside is that this system requires energy to release the water – the base of the device needs to reach 184 °C (363 °F) to wring it out. But the team says the device can tap into waste energy or heat from other systems, like buildings or vehicles.”

I guess it’s fairly hard to get 184°C of heat out of buildings. Getting it out of ICE vehicles is easier, but the device will add weight to the vehicle, and those are on the way out (slowly).

So, that leaves getting it out of waste energy such as excess solar or wind energy. If that’s your heat source, an important metric is “how many Watt hours per liter”

I skimmed the paper. AFAICT, it only mentions usage of current state of the art devices, at 11 to 23 kWh/l, compared to 5 to 7 kWh/l for conventional passive systems.

What did I overlook?

Getting 184c out of a typical car engine won't be easy. You might use exhaust gas but that would be difficult to regulate and seems wasteful. But if you have a car engine then you have a fuel source. Getting 184c out of a gasoline flame is dead simple.

What humidity levels do the conventional passive systems work at?

In regions where there’s excess solar energy and insufficient humidity, the tradeoff seems maybe worth it?

Excess solar energy brings to mind stuff like putting it through solar panels, which can be limiting. But if we just need to convert photons to phonons, no need to stop by in electron-vill, a big dumb array of mirrors could do it, right?

Yeah, no need to do sunlight->electricity->thermal as mirrors would be much more efficient.

Hmm, desert sand can typically reach 150-200F, so there's a start.

And a couple of mirrors can double it.

> The potential downside is that this system requires energy to release the water

Damn you physics!

the copper foam is a really nice idea. for those not familiar with the problem space, the issue is that when you condense water with an adsorbent or other desiccant, it releases a lot of heat, which limits how fast you can condense water: quickly enough your hot desiccant is in equilibrium with the air until you remove some of that heat

nrel did a record-breaking design in the last couple of years with i think calcium chloride on aluminum fins, optimized to provide air conditioning (cooling) rather than water harvesting. if you're interested in this news item you might want to look that up, i don't think i saved the link

(how do they keep the chloride from eating the aluminum? i don't know, maybe i'm misremembering. zeolite avoids that problem)

my own thought is that you ought to be able to rapidly blow the air through a closed loop consisting of a recuperator and the desiccant, thus allowing it to reach the desiccant's deliquescence humidity at the temperature of the temperature reservoir the recuperator interchanges heat with, rather than at the brine-bulb temperature of the desiccant (zeolite doesn't form a brine or have a deliquescence humidity but the principle is the same). this will surely have a lot more frictional losses than simple passive conduction through copper or aluminum, but on the other hand, it's a lot easier to fabricate

in my proposal, once you've reached the desired low humidity inside the closed loop, you open it up and pump your charge of cool, dry air into the place you want cool, dry air, and then begin the desiccant regeneration process with new air circulated in the same way, but passed through a heat source

a somewhat more elaborate version of the system uses a series of heat reservoirs at different temperatures to recover about two thirds of the heat rejected at the first recuperator, using it to heat the regeneration air

but who knows, i haven't built a prototype yet, and my grasp of thermodynamics and psychrometrics is shaky at best; maybe the idea is flawed in some way i haven't figured out

The news article is a little light on details. Link to the original research below:

https://pubs.acs.org/doi/10.1021/acsenergylett.4c01061

Of note - the paper describes the theory and construction of a benchtop proof of concept. This has not been deployed at scale. Also of note, this is not entirely passive, requiring energy input to achieve a yield.

Hmm, This has got me wondering if I could use my daily ~4kWh spare solar energy for watering my dozen chilli plants, maybe something like a dehumidifier running outdoors. It is hot here, and in recent years has some higher humidity in summers. I'm guessing the extracted water is ok for plants?

Well, doing some math, energy efficient dehumidifiers look to be around 2 L/kWh for midrange RH numbers. (Which is much better than the systems in the article.) So you could get maybe 8L per day.

Probably doesn't compare very well to rain water storage. A standard blue barrel will store 250L, or about a month's worth of solar dehumidifier production. Can do some more math on roof surface area and rainfall to work out barrel requirements.

Is also not economically great - e.g. at $0.20/kWh your electricity is worth about $1.6, but in my municipality 8L of water is worth under $0.03.

Valid good points, but it doesnt rain most of the year, and it would cost me to be grid connected. Connection fee, taxes, hidden taxes, and they dont pay for excess above what you use over the year. Hence off grid with some batteries and spare capacity.

I saw a unit for 149e that claims to extract 12l/day, only 210W, compressor based, but you are right of course, equivalent water is a couple cents a day! quite some time for ROI. Probably solving drinking water, which is currently a supermarket run for bottles would be a better investment.

> in air with 30% humidity (classed as arid)

TIL my house is arid

Most wood products, thinking my floors and my actual made of wood dressers, want 35-55% humidity year round. For me I have to add back humidity in the winter, and take away with humidity in the summer.

We had these on my uncle's farm. They are finicky especially in dry environments with lots of sunshine. Robots can assist with the repairs and programming. They can be difficult to find second hand, but if they can program a load lifter they can probably do it.

I think you had the moisture vaporators, not these harvesters.

To keep them yp and running do you need power converters?

That was mainly just something my friends and I messed around with, but primarily it was an excuse to get to Tashi Station - so much cool stuff there.

I'm sorry for your loss.

Thanks - it's been a rough few years. Lost my aunt and uncle, my dad, and pretty much all my other relatives except for my sister. I've tried dealing the anger in healthy ways but despite my calm outer demeanor, I am quite angry and generally wearing all black these days.

Totally relate, I also hate the sand it gets everywhere.

I didn't realize you had a sister!

I bet you and your sister have a "close" relationship.

"So... Luke has a sister!" - Darth Vader https://web.archive.org/web/20240706024024/https://genealogy... - Jonathan Brown

Tell me your Luke Skywalker without saying your Luke Skywalker

Finally, thunderf00t has something new to make a video about that isn't beating a dead horse.

Haha, I enjoy thunder’s spirit, but his vids are so drawn out and repetitive that it makes them hard to watch.

It's Hacker News. Most of the people here are lot smarter than him.

Don't dismiss the guy so easily. For example take a look at one of his papers https://www.nature.com/articles/nchem.2161 and the correspondong video https://www.youtube.com/watch?v=LmlAYnFF_s8

Ironic. Uses heat to harvest water.

Why do you consider that ironic?

Probably because vapor in the atmosphere condenses more easily as temperature goes down.

But even then, in what sense does it go against expectations?

Normally, vapors condense and cool and release heat. This uses heat to cause condensation.

The heat is for desorption, not condensation. After the water vapor is desorbed from the adsorbent, it's cooled in a condenser.

I've always wondered about these sorts of things.

Do they actually make "drinkable water"? If it is distilled water, it is not drinkable, it is dangerous and will leach necessary minerals out of your body.

Distilled water is very drinkable for a long time. You just need to make sure you get the minerals from other sources which are readily available in deserts. For instance in Kuwait that relies 100% on desalination plants for its water supply, they mix in 10% sea/brackish water to replenish the minerals.

No, it's a dehumidifier and you're not supposed to drink dehumidifier water.

>11.15–22.81 kWh/L

Goodness that's a lot of energy to generate a liter of water.

Just a hint at the crazy amount of power available from the sun we take advantage of without knowing.

So, somewhere in the area of a Tesla battery at full charge to get a gallon (+/-) of water.

I saw a video demonstration of this product in a science context. Incredible to see it working completely passively, and also a different model with low electrical load assist.

This one requires the material to be heated to 363°F 24 times a day to wring out the 1.5gal of water. That's a lot of energy spent for very little water.

there is a completely passive device capable of deriving water from the air in a desert, without any electrical inputs, in the demo I saw. It is based on molecular-level action in engineered tube materials.. like a honeycomb but with chemical properties at a very small size, repeated in long stretches like cloth.

Molecular seive or nanotubes?

Is is a dehumidifier? Fins, requires energy, some part gets hot. Yep its a dehumidifier. Dry areas are dry because there is no humidity to condense and fall as rain.

> harvesting 8.66 L (2.3 gal) per day per kg of material, but these tests were conducted at 70% humidity

This is the kind of thing we should be putting a lot of resources in figuring out.

Nothing to figure out, not feasible just by simple basic physics. These types of machines have been busted to death. Sort of like investing resources into harnessing perpetual motion.

> This is the kind of thing we should be putting a lot of resources in figuring out.

Why? A lot of manufacturers have figured this out, the technology is called a dehumidifier.

Anyone know of DIY plans for this kind of thing?

heavily patented materials science in the core - scaling their products in various ways is certainly discussed

I saw one recently where they used something that looked like very fine plastic filament fishnets layered on each other in this large cornucopia looking tower. I think they were capturing the mist as it came on and off a desert mountain side

Yes, take two heat pumps in series and run one as AC and another as heat and you'll get far more than 1.5 gallons of drinking water out of arid air than this

Any dehumidifier will drip water as a byproduct, air conditioners included. A friend has a tubes from her AC going to her carnivorous plants which like the distilled water.

Another dehumidifier from MIT Thunderf00t is going to have a field day

Reply on news.ycombinator.com