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Engineers at MIT and in China develop desalination system which could produce freshwater that is cheaper than tap water (news.mit.edu)
submitted 2 years ago by to c/technology@lemmy.ml
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It looks like the paper is paywalled and not yet on scihub but i did find 38 pages of supplemental information with more details than the article.

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[–] 44 points 2 years ago* (last edited 2 years ago) (5 children)

While this is a cool development I would recommend tempering expectations. The cost of tap water is exceptionally cheap and the claims made here likely take these estimates to the extremes. The economics of scale likely don't match up.

For example, tap water in my city costs ~$0.04 per gallon, at 5 liters per hour, 0.264 gallons per liter, 24 hours per day, for 5 years is $2,312. So saying they can make it for less than the cost of tap water doesn't mean it's affordable.

EDIT: Forgot to convert from liters to gallons

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  • [–] 36 points 2 years ago (2 children)

    For example, tap water in my city costs ~$0.04 per gallon, at 5 gallons per hour, 24 hours per day, for 5 years is $1,752. So saying they can make it for less than the cost of tap water doesn’t mean it’s affordable.

    Or maybe the product just isn't for you, but for people who pay significantly more for, or possibly don't have access to drinkable tap water at all.

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  • [–] 8 points 2 years ago*

    But furthers the point I'm making. If your water costs more than mine then the potential price of this machine is even higher and the base price is already expensive as is. If this was truly a cheap and affordable alternative for people's in need then it likely would have made that price point a major point of the article.

    Just because it's cheaper than an alternative doesn't make it affordable.

    EDIT: Also the article says

    "the team estimates that the overall cost of running the system would be cheaper than what it costs to produce tap water in the United States."

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  • [+] -7 points 2 years ago (1 child)

    It's a solar distillation machine. The compact size is useful but there are dozens of ways to do this for almost free as long as you were within reach of an ocean. You can dig a hole in the sand put a piece of clear plastic over and a catch basin in the center and do the same thing. It's interesting but not really earth-shattering.

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  • [–] 13 points 2 years ago (1 child)

    You can't "just do this" because you live by the ocean. You're over simplifying it because you aren't impressed.

    For coastal people of impoverished or war-ridden locations with tainted or unavailable groundwater supplies, this is amazing if it becomes reality.

    Your normal isn't most people's reality. Clean drinking water is not ubiquitous.

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  • [+] -11 points 2 years ago (1 child)

    Are you telling me you can't make a solar still out of a sheet of plastic a bowl and a hole in the sand at the beach? Because if you don't think that works we have no further need to communicate.

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  • [–] 11 points 2 years ago (1 child)

    Hope much drinkable water are you generating with your sand hole and plastic? This thing can allegedly generate liters per hour. Enough to sustain a decent sized group of people.

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  • [–] -2 points 2 years ago* (last edited 2 years ago)

    The numbers provided are qualified with "if they can scale it" up. So they don't even actually know that they'll get that rate.

    Edit: MythBusters did it They pulled a about a half cup an hour out of a 6-ft wide hole. Best case if you are engineering this you could put a frenzel lens in front of a pan of salt water your energy conversion would be like 99%. For using sunpower, The amount of water you're going to extract is directly related to how much energy you can collect.

    I'll believe their numbers when they actually bother to scale it.

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  • [–] 7 points 2 years ago (1 child)

    The big one being "if it could be scaled up to a size of a suitcase"

    That's not very lofty, which makes me all the more skeptical.

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  • [–] 5 points 2 years ago (1 child)

    Your tap water is expensive! Is that a typical rate? Its $551 for me for the 5l/hr for 5 years. $0.0075 per gallon. This is in UK. Its billed at £1.98/1000l.

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  • [–] 1 point 2 years ago* (last edited 2 years ago)

    It's complicated, typically US rates aren't a flat $/gallon. Most have flat fixed costs (meter fee, availability fees, etc) and then the actual volumetric rate charge is tacked on top of that. In my city the rate is additionally tiered, so the more water you use the more those later gallons cost. Most residential users fall into Tier 1 though, up to 4 CCF (Centicubic Foot or 748 gallons) per month, which is billed at $1.89 per CCF or $0.002526 per gallon.

    So it's hard to use the rates alone as there are additionally fixed rate costs (around $10 a month) and other usage is billed differently (commercial and industrial have higher flat rates as well as higher flat volumetric rate). The result is that commercial and industrial users pay higher rates than residential.

    Luckily, my city also publishes raw statistics which indicates that, all things averaged together, the water costs around $0.04 per gallon.

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  • [–] 5 points 2 years ago (1 child)

    I have family that can't drink their tap water because it's practically brackish (is was entirely brackish when someone pierced the aquifer boundary and created a hole that filled the underground reservoir with the nearby sea water, that lasted about 18 months, the entire community was on water that was being trucked in while a new well was discovered and drilled), their water is insanely subsidized, and still pretty expensive. The community is about 200 houses, each with access to Ocean/River inlet water, I don't know a single one of them that wouldn't go for this option. Their water is so heavily mineralized that filters lifetimes are hours to days. And then maybe they can allow the aquifers to refill, and maybe their houses wouldn't be sinking as quickly...

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  • [–] 1 point 2 years ago

    Hey, I'm not saying this technology doesn't have a use, and maybe if it's stupidly expensive it will be heavily subsidized. The point I'm making is that it "likely" isn't the solution to world wide water scarcity.

    Another user commented that desalination is a grift, it's not, the market forces just aren't there yet to push its large scale implementation world wide. However, the idea that an upcoming technology may theoretically scale up and be the same economic scale is historically unlikely.

    Historically the trajectory of this sort of technology is that it will define technology for the next 20 years (Nobel Peace Prize or more), or it will be bought up and buried by a big corporation (goodwill isn't typically good for capitalism), or it won't scale up as predicted and will be a major nothing burger.

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