Advances are always welcome, but it's worth noting that desalination works economically right now.
In the last 15 years large scale desalination has become practical. It's one of the great engineering feats of our time.
We can now generate it at scale for less than $.01 per 6.4 gallons. This includes the cost of the electricity, which is about half the expense.
San Francisco charges $.02/gallon to residents, 12 times that price. It's now cost effective for any coastal city in America to supply residential water this way.
Lots of people still think desalination is still impractical, because it was 20 years ago. They just haven't learned about the new tech.
Residential water is not the issue, not even commercial water. Desalination still doesn't work for the vast majority of users: agriculture. 0.02$/gallon is far to expensive when farmers need acre-feet of water (300,000 gallons). Delivery of such quantities from the ocean to inland farms is also impractical, and cannot conceivably be made so.
That's why they draw from rivers and aquifers.
I think evaporating large areas of salt water could increase the local air moisture level substantially. That with the passive desalination could make water much cheaper in coastal areas.
It's also worth asking how desalination can be used in say afforestation or ecosystem restoration, to improve evapotranspiration of water over a landscape where appropriate.
Corn will need about 24" of water each crop. So, if there is no or little natural rain, two acre-feet of water per acre. There is no concievable method of transporting such amounts inland. It would require energy enough to reverse the flow of rivers.
The confusion comes from naming American units "imperial" - after British, and having international - metric - system created by the French revolution, with "liberte" an important goal. So it could be argued that it's actually SI which has freedom units. On the other hands, Americans are quite often characterized as freedom "distributors"...
Most Americans that I have pointed this out to look at me in disbelief. The vast majority have never heard of US Customary Units. Whenever they refer to their system of measure they say imperial, and many are unaware that volume measure in the Imperial system is different from US Customary. I fought again the use of imperial as the name for the system for over twenty years in a multinational company to no avail.
Send them this handbook from NIST! :) Section 2 covers all of the customary measurements, some with names hardly anyone knows (Apothecaries Units? Gunter's Chain Units?)
I've never met a Canadian who gave their height or weight in metric units.
Or a recipe in Canada that doesn't set a temperature Fahrenheit. Also: the size of TVs and screens. Or paper.
News articles in particular tend to go out of their way to use strange units of measurement. Bananas, fishes, football fields, car lengths, swimming pools... Anything but SI system of units. Even the feet gallon pound values are rare finds that need perseverance.
Eagle wingspans isn't something I've seen used, but the football fields unit does make sense when talking about something which is relatively long (can be measured in 1/2 to 3x the length of such a field).
If you tell the average (US) person 1000 feet, they won't be able to envision it. But if you say "a little more than three football fields", they can visualize that.
The point of strange units of measure is just to make a quantity relatable.
> Chairman of the Committee on House Administration, Bob Ney, renamed the menu item in three Congressional cafeterias. The political renaming occurred in context of France's opposition to the proposed invasion of Iraq
"Refuse to go to war with us? We'll... remove you from our cafeteria menu! Take that!"
The country that landed men on the moon adopted the metric systems as the basis of its measures before most other countries and programmed its moon landing systems using metric.
The country is a metric country (see: Official definition of the US foot).
Its citizens, however, largely still roll coal measured by chains to the hogshead.
The previous moon thing is a joke and at least partially an explanation for "freedom units," which is a joking (I think) commentary about the citizenry's beliefs about "their freedoms," and somehow these freedoms translates to freedom from using the metric system when they roll coal along a couple furlongs of interstate (in a truck that contains only metric fasteners.)
If you're exposed to figures written in scientific notation, then learn scientific notation (it's not even hard, the number represents the number of zeros you'd write if you had to write it entirely: 5000 = 5⋅10³ / 5E3, 0,0003 = 3⋅10^-4).
As said above, it has nothing to do with the metric system anyway, it's just about dealing conveniently with very big or very tiny value (1⋅10^-9 meter is 3.9⋅10^-8 inch, no matter the unit you're using you'd be using scientific notation to express things that small instead of dealing with 8 or 9 zeros).
Thanks for the advice I never considered trying to learn scientific notation. I think the way the problem manifests in combination with the metric system is that the metric system seems to have an extra 1,000 that may or may not apply.
I think my particular problem is when dealing with electricity and physics.
I never once blamed the metric system and identified the problem as my in ability to comprehend values in scientific notation. I appreciate I shouldn't be so dumb and try to read about things I don't understand. It's a life long struggle.
> is that the metric system seems to have an extra 1,000 that may or may not apply.
You may be getting confused over prefixes vs base units because some pairs of prefixes and base units are so common they sort-of end up treated as a unit in themselves.
E.g. "kilo" is not a metric unit, but sometimes used as short for "kilogram", where "kilo" is the prefix for 1000 and "gram" is the metric unit. These prefixes are consistent for all metric units.
"Kilometer" is another popular unit, which is never called "kilo", lately I heard it's informally called "click" in US. Logic is the same, kilometer means a thousand meters, and meter is the base unit of length.
I once worked with someone from Egypt who used "kilo" for kilometers. He's the only person I've met who did that. I've no idea if that was just a personal quirk or if that was a common shortening elsewhere in the world.
No, just because historical :) . There's the system centimeter-gram-second, which is used e.g. for electromagnetic physics, it has its own quirks, at least with "centi"-meter unit name.
I don't know what to say other than I have a hard time reading scientific notation and the metric system. The metric system seems to lend itself to large numbers that are small quantities on the human scale.
> My problem with the metric scale is that when values are expressed in scientific notion they lose all reference to me.
As if the two are connected. But my point is that scientific notation is not part of the metric system at all. If you problem is with scientific notation, that is a problem with scientific notation, not metric.
If anything, with metric units most people outside of the sciences will use the metric prefixes and never ever use scientific notation at all.
It always amuses me when I watch a machining video from someone using metric. I've just been exposed to too many US machinists and am much more familiar with "thous" and "tenths" but baffled by microns and 0.02mms.
Is handling leftover brine accounted for in the calculations?
You know you cannot simply dump it back into ocean in one place. It is also a problem in Gibraltar or so to say they have it figured out but it costs them a lot of money.
Run a pipe out a few miles to where the ocean drops to a few hundred meters and the currents are strong and job done. This is not a technical challenge in any way, just a minor cost overhead. Pumps and pipes; that's all you need.
This is not the reason the US doesn't desalinate. It is actually actively making things worse in the places where it can still extract water from aquifers. Removing the water allows salt water to penetrate those thus destroying the local ecosystems. It's also speeding up the desertification of other areas.
Desalinating ocean water (done right of course) is part of the solution, not the problem.
Solutions like discussed in the article are more interesting for smaller/rural setups. Interesting but desalinating at industrial scale is a solved problem already. Can it be done cheaper. Probably and that would be nice. But it can be done economically right now. The largest challenges here are bureaucratic, not technical.
I'm pretty sure there's nowhere in the mainland UK that just dumps all its raw sewage in the sea or in rivers - everywhere on the mainland was retrofitted with sewage treatment a while back. Now, those retrofits aren't perfect and sometimes raw sewage still overflows due to storms for example but we don't just routinely discharge all the sewage into the sea. There are still places in Spain, Ireland, and some other EU countries that haven't managed to build sewage treatment yet and actually do discharge all their raw sewage either into the sea or into rivers leading to it. (Yes, this is almost exactly the opposite of the narrative pushed by the British media.)
Gibraltar apparently doesn't have sewage treatment because they have some salt-water flush system for toilets due to fresh water historically being so expensive there and they seem to have had difficulty getting a treatment system that works with that.
Boil-water notices due to cryptosporidium and other nasties in drinking water are somewhat common in some places in Ireland. The difference in water quality and hardness between places that aren't very far apart is pretty striking.
This is probably fine for non-industrial wastewater tbh. Feces, urine and biodegradable toilet paper aren't putting anything in the ocean that isn't already there in vast quantities.
It's honestly not so wonderful an idea when you're downstream of it, which given the Med has a significant and continuous in-flow, means that people along the Costa del Sol swimming in the sea are probably having more than their fair allowance of Gibraltarian effluent.
That’s not directly comparable to residential rates because you now need to pump that water up hill and through a distribution network to customers. Desalination occurs at sea level and getting that to anywhere but costal cities is even more expensive.
Further, 0.01 cents per 6.4 gallons is 500$ per acre foot which is horrifically excessive for agriculture where most water is used. Using it for Alfalfa would cost more than 10x what the crop is worth. Desalination is therefore still only viable in very niche areas without heavy subsidies.
Or maybe the unsustainable depletion of groundwater for the purpose of growing alfalfa is only viable in very niche areas without heavy subsidies?
The number they are quoting is 0.41 $/m^3. Per capita water withdrawals (including agriculture) in the US were ~1200 m^3 in 2015 [1]. That means the cost per person to convert all residential, industrial, and agricultural to desalination is only ~480 $/(person * year). Or approximately 6/1000 of US GDP. Even if we assigned all of that cost to agriculture and food, all that would mean is that the average person's food budget would increase by ~480 $/year. That is sizeable, but not even slightest bit infeasible. If we really needed to we could just assign 3% of the US federal government budget to preventing death by starvation and thirst by achieving full water independence.
Desalinated water is only uneconomical in comparison to unsustainable groundwater depletion. On a absolute basis it is very affordable and would not constitute a material problem for the US or any other developed country.
Subsidies is arguable as groundwater isn’t necessarily useful unless you pump it out. How much to value that finite resource isn’t obvious but letting it run out is a self correcting problem.
Anyway your numbers aren’t even close. Water needs to reach people not simply exist. Groundwater depletion really isn’t a thing in the east cost, it’s mostly a thing west of the Mississippi and mostly at fairly high elevations.
To offset water withdrawals of people living 2km above sea level that 1200 m^3 of sea water would need 6480 kWh before consideration inefficiencies. For much of the Midwest you’re spending more on pumping than desalination, but you also need pipes etc.
Oh geez, 6840 kWh. At 0.10 $/kWh that is ~700 $. Added onto the 480 $ that would increase the costs to nearly 8% of the US budget. If it takes a 8% increase in the government budget, I prefer dying of starvation and thirst, said nobody ever.
I am being a little flippant here. Transitioning to a desalinated water economy is a gigantic megaproject. I am not including the costs needed to add all the transport infrastructure, but we also do not need to convert over 100%. We only need desalination where we are consuming water in excess of water renewal rates. And if you need excess water you will need to move your business to where water resources are cheap. That or your business and people die of no water. I know what I prefer. Luckily, highly productive farmland which consumes the vast majority of the water is generally on flat, low elevation ground where transport costs will be low.
Desalination is a viable solution. Are there challenges? Sure. Can you do it without any sacrifices and without changing your lifestyle at all? Probably not. But if your alternative is insufficient freshwater resources desalination can solve that economically at scale at a modest cost and with relatively minor sacrifices.
Except this isn’t about drinking water its just agriculture and not even agriculture used inside the US.
Spending 8% of the US budget to subsidize exports would be lunacy. Ban Alpha exports from California largely solves the problem within the state as does a host of other possibilities like say charging a fee for using an aquifer.
Anyway it’s a self correcting problem, when farms can’t pump out water they will shut down reducing water use. The US is such a massive exporter that none of this will be noticed by US consumers.
Then don’t do that. You are the one who brought up alfalfa, the classic example of a low value good being subsidized by unsustainable and flagrant water usage, as evidence that desalination is not viable.
I pointed out how even if we decided to support and subsidize the moronic use cases the US can still easily support a desalinated water economy if we had to.
In actuality, if we moved to bulk desalination we would see a reconfiguration of water usage to higher value usage since water would be immensely more expensive. However, despite being much more expensive, even if we massively overestimate water usage by including water wasteful export crops, desalination still ends up being viable including the usage that would almost certainly disappear if they did not get to defray their depletion externalities.
Massive overestimate comes out reasonable. Therefore correct estimate will also come out reasonable.
You're forgetting to take into account transport costs.
Want to pump that cubic meter of water 100 km inland and the energy cost alone will be over $1/m^3. Ignoring pumps, piping, maintenence, land purchasing, cabling, planning permission, etc etc.
The price is not really for the water, which is too cheap to Meyer, but for the infrastructure, which is per liter transmitted a much higher fraction of the cost than industrial/agricultural users.
Desalination plants are only that cheap at scale, if you’re in a costal city then raising water 300 feet isn’t a big deal. If you’re in a small community in a low density area or a large one 6,000 feet and hundreds of miles above sea level the math looks very different.
Many people live near the ocean. It doesn't have to solve every problem. Also I don't think many people are living hundreds of miles above sea level :)
The problem is it solves basically none of the issues.
Where people live isn’t where people consume aquifers faster than they are replenished. Across much of the east coast farmers don’t bother with irrigation because even the cost of pumping water from a well and delivering it to their fields isn’t worthwhile.
West of the Mississippi the amount of rainfall drops and therefore the need for water skyrockets. https://us-canad.com/rainfall-usa-map.html The difference between 150 inches per year of rainfall and less than 25 is huge.
I know we've had decades of brainwashing trying to blame individuals for water and energy (ab)use, but residential water is almost never where the problem comes from when talking about freshwater: the problem comes from agriculture, and even at the rate you're talking about above it's not economical and we're still draining aquifers at an alarming rate.
Since this is news.y, I'll frame it in ST:TNG terms:
In one episode they discovered a way to use the transporter to become young again. You would think eternal youth would be a big deal, right? Nope, it was never mentioned again.
Eternal youth using a transporter would have been shouted from the rooftops.
it was pretty noticeable to me. i don't think it's the groundwater specifically but they started treating the water with chlorine as part of the change, which you can definitely taste. i installed a filter under the sink and at least that fixed the problem for me... but it did make me reflect on what's in our water, in general.
I certainly agree about the great strides that were made, but there is much more room for improvement: while desalination has become cost effective for residential volumes, further improvements could enable cost effective desalination at even larger volumes for irrigation, and prevention of drought enabled wild fires, especially considering rising temperatures (air and soil).
This is some blog's restatement of an MIT press release, neither of which appear to name or link to the actual paper or other useful writeup.
But judging by the researcher names and the date I believe the actual paper is titled "Extreme salt-resisting multistage solar distillation with thermohaline convection" which appears to be available as a PDF at https://www.cell.com/joule/pdf/S2542-4351(23)00360-4.pdf
the first link in the sidebar of the MIT writeup is to the paper you linked. it'd be nice if they linked it in the the body copy as well but here we are.
the blog post in question is written by steve novella, who also produces _the skeptics guide to the universe_, a fairly popular science and skepticism podcast. it reads like more than just a "restatement of an MIT press release" to me. i don't love the entirety of the message but it's not just a summary of the paper or a summary of the summary of the paper.
Ah, I stand corrected. I overlooked the PDF link over in the sidebar and am less disappointed by the MIT News writeup now (although I do still wish they could have copy-pasted the diagram from page 1 of the PDF into their photo carousel, reading those several paragraphs of text attempting to describe the device's construction was downright painful and the reason I gave up and went looking for the paper).
My understanding the big drawback of desalination is the residual substances. They trivialize it in this article as salt, but it’s actually a slurry of heavy metals and other toxic stuff, with lots of salt.
This system (better described here [0]) simply washes the brine out as it makes it into the ocean, so the hypertoxic concentrate isn’t an issue. (Original paper here [1])
“Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers.”
Yes, but after the fresh water is used, it will flow downwards and rejoin the ocean.
It's called the water cycle for a reason. Water doesn't disappear after being used.
In any event, the Greenland ice sheet is on track to melt over the next few centuries and add 2,850,000 cubic kilometers of water to the ocean. We're not in danger of making it too salty with desalination.
Sure, but it's about locality/concentration - it's the difference between walking through rain without a hat, and getting a bucket of water to the face. It takes time for the salinity to even out, and in the meanwhile things in the area are exposed to way too-concentrated salt.
Or perhaps it's like drowning - sure, people can swim for a total period of hours a day, but they're never underwater for a continuous duration of more than a few minutes in a row.
Not the sea, but the localized area might have a brine lake, which is a deadzone for marine life there. If diffused over a large area, it will not have an impact. The only problem is cost.
The minuscule amount of salts being added into the ocean does nothing to the whole ocean. One river will have washed out more salt.
Salinas or salt marshes are highly productive for native species adapted to high salt levels. Brine shrimp feed Flamingoes (if you are lucky) or other aquatic bird species.
No, you can't just assume this salt burden is fine, and that we get good salt marshes from it, but it's also not entirely true that high salt level brine is going to "destroy" the ecology. It's going to alter it, for sure. That isn't always very good, it depends what else has also destroyed the ecology, and what upsides there are to making a salt marsh.
Except this article is about irrigating with sea water to mix with fresh water. A salt water marsh is not a particularly concentrated salt water, and is diluted by rain and water flow above and under ground. The brine from desalination is extremely concentrated and toxic. In theory you could dilute it with large amount of fresh water to make salt marshes, but the entire point is to make fresh water from salt water. For a salt marsh you’re better doing as in the article you linked and pumping sea water from the ocean.
Considering the effect of evaporation, I think it would be a non-issue. When oceans evaporate they increase salinity, but then rivers will bring that water back.
The Mediterranean Sea once completely evaporated, leaving a large salt deposit. Later, the Gibraltar barrier broke, allowing water to flood in with new salts, forming a saltier-than-average sea: 3.8 g/100g vs 3.4 in the World Ocean. But that is no problem for marine fauna and vegetation.
This was brought up by someone else in another forum, but do the MIT desalination numbers make sense to anyone else?
They claim that a box with a surface area of about one square meter could desalinate 5 L of water per hour, using nothing but solar energy.
To evaporate one liter of energy of water takes 2.30 MJ, and that's assuming that it's already boiling point (the most efficient temp to evaporate). Solar energy maxes out at about 4.97 MJ per hour per square meter. That’s just a bit over 2 liters – and that’s assuming best case scenario and the sea water is at the boiling point.
So how is this box with 1 m^2 surface area gather enough sunlight to evaporate 5 L water per hour?
Disclaimer: I haven't looked into this at all. But on a first-principles basis, it should be possible as long as the desalination process recovers most of the evaporation energy during the condensation process.
On that note, there are also desalination proposals out there that rely on heat pumps, where great is transferred from the condensing side to the evaporating side. (Obviously additional outside energy is required.)
To get an idea of the scale: the average residential water usage is around 120 liter per person and day in Germany, around 300 in the US.
Assuming you get around 8 hours of operations out of such a box per day, that would be 3m² of land usage for the German usage, or 7.5m² / 80ft² for the US, per person. Doesn't sound great, but not too terrible either, compared to current land use (for housing, cars, infrastructure, agriculture, ...)
That's of course ignoring other water sources, and also that the hours of operation will vary wildly with weather and season.
If your children end up living in a world where water is so difficult to source that something like this is required, then the average households will likely be a lot more frugal than just burning through 120 L a day.
If I weigh 85 kg and measure 185 cm (BMI 24.8, right at the edge between normal and overweight), my body surface to wash is 2.09 m². Let's assume a 3-minute shower at 15 liters per minute, so 45 liters of water. So 21.53 liters per m².
If my weight is 120 kg (140% of above) and I still measure 185 cm (between Obesity I and II), then my body surface to wash is 2.42 m², an increase of 0.33 m². Applying the same ratio as above, at 21.53 liters per m², I would need 52.11 liters of water (115% of above).
So a weigh of 140% results in a water consumption of 115%.
Qualitative argument is right, but the effect is not linear.
That assumes time to wash is linear to surface area. It is harder for heavy people though to wash themselves tho, harder to reach everything including tools, more tools required, more time spent not actively washing while the water runs.
> For a box a square meter in size it can produce 5 liters of drinkable water per hour.
Let’s see if the claim is possible from physics and math perspective.
In one hour the water is boiled to evaporation and then cooled (I presume with some added energy).
Raw sun energy is 1375W/m2 directly hitting earth but after clouds, tilt, material absorption we could say perhaps ~25% efficiency of input energy is captured so 350W. That is 0.35KWh in one hour.
1 hour solar energy is 0.65kWh.
To raise 1C of 1ml is 1 joule. So 100C from 20C of 1000ml is 80K joules, which is 0.02kwh. 5 liters would be 0.1kwh of energy.
0.1 < 0.35. The math checks out. Should be possible to evaporate 5L of water and have some energy leftover for cooling via heatpump mechanics.
How much land would be used?
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Suppose this was put in Tampa since it’s in the sunshine state. We could say 5 hours of sunshine so 25L of clean water / m2 / day.
Per person we’d need (265/25)= 10m2, for a city of ~500,000, we’d need 5 million m2 or 5km2.
Land area of Tampa is 300km2. So 1.6% of land would be used to make water.
5km2 is a looooot of land in one big plot, but not a lot of divided in chunks across where people live.
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If we are serious about global warming and future compfortable survival of our species then we should build homes where the entire roof is harnessing the energy of the sun.
To desalinate, to capture solar into electricity, to heat water.
Shingle roofs are strong snd cheap but if every foot of roof in US sun belt region was covered with solar cells, we’d be net negative for residential energy (produce more energy than use - that energy could supply electric transport).
It would make total sense to live in a solar farm of homes and use energy close to where it is captured.
Our future very much depends on how efficiently we can harness the sun’s energy which is free and abundant.
Roofs should do more than just capture the energy of the sun, it needs to capture and store the water that hits it, because diffusing that water is enormously expensive at a city level. Hint: shingle roofs inject things into otherwise fresh water.
A number of the threads here were discussed over there, including the particularly-interesting observation that concentrated salts are not that much of a concern if the (presumably-locally-consumed) water round-trips out via the same physical location, in the form of sewage / grey-water / etc.
> After careful calculations and experiments, the researchers determined the optimal size for the holes drilled through the perforated material, which in their tests was made of polyurethane. [0]
Really nice innovation, you need holes of 2.5mm to avoid clogging. The tradeoff is between efficiency and maintenance.
The ptfe membranes with 1 µm pore size that is used in this are very expensive.
1 sqare meter of membrane is about 900 USD.
And you need 1 sqare meter for each stage. With a 10 stage device as developed in the article, things start to add upp.
If someone makes a product of this they would probabbly be able to push the price down. We will see. As it is right now PV pannels and an electric desalinator would give allot better returns.
A cubic meter is 1000 liters. If we assume (as you said) that 1m^2 can produce 50L per day, you would need 20m^2 (1000/50) to produce a cubic meter. Not 20,000m^2(!!).
So for 600k cubic meters of desalinated water you'd need 12 million m^2 (or 12km^2 or ~3000 acres), which sounds very doable.
In the last 15 years large scale desalination has become practical. It's one of the great engineering feats of our time.
We can now generate it at scale for less than $.01 per 6.4 gallons. This includes the cost of the electricity, which is about half the expense.
San Francisco charges $.02/gallon to residents, 12 times that price. It's now cost effective for any coastal city in America to supply residential water this way.
Lots of people still think desalination is still impractical, because it was 20 years ago. They just haven't learned about the new tech.
The tech:
https://www.energymonitor.ai/tech/can-desalination-save-a-dr...
Residential rates:
https://sfpuc.org/accounts-services/water-power-sewer-rates/...