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According to the Daily Mail article LA couple win $1.5 million XPrize for radical system that can make clean water from AIR for less than 2 cents a quart, David Hertz and Laura Doss-Hertz have developed a machine that can extract over 500 gallons of potable water a day from the atmosphere for basically free.

The Daily Mail does not have a good reputation for reliable science reporting and a lot of the claims seem questionable to me. The biggest alarm bell for me is the following extract from the article:

The Skywater system relies on a patented Adiabatic Distillation Process, which reduces water vapor to liquid without a gain or loss of heat, according to the company's website.

This sounds to be a violation of the laws of thermodynamics to me, a massive red flag that this might just be some species of perpetual motion machine. It also violates the latent heat of evaporation/condensation effect. However the article also claims that the inventors have won an X-Prize for water abundance.

While I'm sure extraction of water from the air is possible (because dehumidifiers are a thing) the numbers being bandied around here seem like total fiction to me. Is there enough moisture in air for this machine to extract the amount claimed, can it be done "without a gain or loss of heat" and can it be done so cheaply as claimed?

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  • "Is there enough moisture in the air for this machine to extract the amount claimed" -- Where, exactly? In a rainforest, probably. In an area where having "free water" would be great because people are dying of thirst and crops are failing in drought? Doubtful. (And the guys two towns over would get even less of a precipitation chance.) ;-)
    – DevSolar
    Oct 26, 2018 at 7:45
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    Prize seems true: xprize.org/prizes/water-abundance/articles/… - "[Skywater] extracting a minimum of 2,000 liters of water per day from the atmosphere using 100 percent renewable energy, at a cost of no more than two cents per liter." - given 30g water/m^3 for saturated air @30C that could be met by 1m^3 of wet air desiccated/second. Unfortunately the islandsky.com website doesn't explain beyond "patented Adiabatic Distillation process" but notes "not designed for dry or cold climates"
    – Tom Goodfellow
    Oct 26, 2018 at 7:48
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    "Adiabatic Distillation Process" is just a fancy way of saying "pressure liquefaction"... I don't see where I would award a prize for that. ;-)
    – DevSolar
    Oct 26, 2018 at 7:59
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    There is nothing strange about the process. Scrape away the corporate BS and what you have is simply a condenser: make humid warm air come into contact with a chilled surface and — viola — water. Take a can of soda from the fridge on a warm day, place it on the table and you see the effect in play; soon you will have water droplets on the can and after yet a while it will have wet the table. The only hairs that need splitting about the claim is the supposed running-costs.
    – user32299
    Oct 26, 2018 at 8:00
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    Obviously, a conventional electric dehumidifier (such as is found in many homes in the southern US) can extract water. The max rate, in the average home, is about 10 gallons per day. You'd have to scale up the typical home humidifier by a factor of 20, at least (with a much larger supply of moist air), to approach 500 gallons per day (assuming economies of scale). To achieve the efficiency stated the associated heat energy would have to be recycled more effectively. Precisely how this is (supposedly) done is unclear, in the several web sites I checked.
    – Daniel R Hicks
    Oct 26, 2018 at 12:06

2 Answers 2

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Can you extract over 500 gallons of water from the air a day for a few cents per bottle?

Well, first, the "500 gallons" part is an irrelevant distraction. If there's a machine that can extract 1 gallon a day, then 500 of them would be able to extract 500. What about the "few cents" part? That falls into the "technically true" category. However, there are a variety of other implied claims that are false.

Is this how much it will cost in practice? The 2 cents/liter figure is the "best case" scenario. Not only will most places have less humidity than is needed for that level of production/extraction, but the places with high enough humidity, where we would see the "best case" production, already have rain.

Is it revolutionary? A quick search on Amazon gets a dehumidifier that can produce up to 4 gallons a day at 170 to 260W. Taking the upper end, that's 24*260 = 6.240 kWh, or 1.560 kWh/gallon. The Skywater system, on the other hand, lists its efficiency at 2kW/h per gallon. If we take this as 2kWh/gallon, that's 78% of the efficiency of the first humidifier I found on Amazon.

Is this cost efficient? The website says that this is cheap and reduces carbon emissions, but that depends on what you're comparing it to. Certainly, fancy imported water at $2/liter is going to be more expensive than this, and probably have a higher carbon footprint, but compared to tap water, it's ridiculously expensive. 2 cents per liter sounds cheap, but that's $20/m^3. According to moneycrashers, tap water costs $2 for 1000 gallons. That's $0.53/m^3. Now, you can say "What about places that don't have tap water?", but most places that don't have tap water also don't have electricity, at least not at $0.10/kWh. And let's look at the other alternatives. According to The Guardian, it costs $18/m^3 to ship water, and desalination costs $1/m^3. Now of course shipping costs vary, and perhaps there are remote areas where it will cost significantly more, but again, where are those areas going to get electricity? As far as places where this would be useful (apart from, again, comparing it to bottled water), we are left with reasonably humid areas that don't have rain or saltwater, and are too remote to ship water. I'm not saying these places don't exist, but they certainly aren't common.

Besides the kW/h flub, there are several other red flags

Alkaline-ionized water is fundamentally different from conventional water because the size and the shape of the water molecule cluster has been reduced in size and changed to a hexagonal shape,which allows the water cluster to pass through our tissue more easily.

They claim that this water hydrates "six times more" and "washes acidic waste and other toxins from your body". They also claim that it eliminates the need for carrying heavy water bottles and needs no plumbing ... so how does the water get to you? Is the machine indoors? Do you have to get the water from the machine?

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  • What does copy/paste issues on their website have to do with the claim? And kWh vs kW/h? And then criticism on what's plainly puffery?
    – user11643
    Oct 27, 2018 at 23:35
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    "If there's a machine that can extract 1 gallon a day, then 500 of them would be able to extract 500." That's not usually how scaling works; there's a big difference between one machine that extracts 500 gallons of water and 500 machines that need to be meters apart doing the same to not get in each other's way. The former would be significantly more useful.
    – Erik
    Oct 28, 2018 at 7:05
  • @fredsbend It not just "puiffery", it's psuedoscience, and it reflects on their credibility. The C/P stuff is a bit nitpicky, but it is a bit unprofessional.
    – Acccumulation
    Oct 29, 2018 at 3:08
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    @Erik I started out discussing the literal claim, and concluding that it was technically true, then moved on to whether the implied claims are true. If we're discussing the literal truth of the claim, then you can in fact get 500 times as much from 500 machines as you can from 1 machine, if they have sufficient separation.
    – Acccumulation
    Oct 29, 2018 at 3:11
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    @PoloHoleSet That comment displays a quite large lack of understanding of economics.
    – Acccumulation
    Oct 30, 2018 at 14:55
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After a bit of research, I'm inclined to call this one plausible.

From the XPRIZE site we find:

Led by Architect David Hertz, https://davidhertzfaia.com with Rich Groden co-inventor of the patented Skywater technology http://islandsky.com is a collaboration of leading experts in sustainability and systems thinking committed to the water, food and energy nexus.

A search on Google Patents for the assignee Island Sky Corp reveals four patents (two of which are abandoned,) all dealing with potable water collection and production.

The most recent is US20110048038A1, Multipurpose adiabatic potable water production apparatus and methods, published in 2011.

Island Sky produces several products today; the following claims are from their marketing materials and seem to reflect ideal conditions:

Skywater Harmony requires 2 kiloWatt-hours per gallon, as does the Skywater 14.

The larger Skywater 300 requires 8 kiloWatt-hours, but that seems to produce 4-5 gallons.

The price for a kiloWatt-hour of electricity varies from place to place, of course, but generally looks to be on the order of ten cents.

The original claim is "less than two cents per quart" which would be less than eight cents per gallon. The original claim also seems to be referring to operating costs exclusive of capital costs, depreciation, maintenance, and the like.

Based on this information and weighing it against the possibility that the parties in question have somehow managed to deceive the XPRIZE committees, I'm inclined to conclude that the claims here are plausible.

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    It's worth noting the claims was $.02/quart. Many folks may not know that there are 4 quarts to a gallon: hence $.10/gallon ~= the claim.
    – aslum
    Oct 26, 2018 at 18:42
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    They did not "receive" 4 patents. There are two patents and two applications. The two applications look abandoned at this point so unlikely to ever be granted.
    – Eric S
    Oct 26, 2018 at 19:26
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    1. How many places are there that 1kWh costs 10 cents, and don't have tap water? 2. How are marketing materials confirmation? 3. How much does it cost to make this? Just operating costs isn't a valid metric without looking at manufacturing costs. After all, you hook one of these up to a solar cell, and the operating costs can be zero, if you don't include the cost of the solar cell.
    – Acccumulation
    Oct 26, 2018 at 19:30
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    @Acccumulation The only use case this makes sense for is as an alternative to desalinization.
    – Loren Pechtel
    Oct 27, 2018 at 13:13
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    The existence of a patent doesn't prove anything. While the USPTO will reject most patents for known impossibilities (like perpetual motion machines), they do not verify the practicality of other claims.
    – user42059
    Oct 29, 2018 at 1:38

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