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I think you’re still going to get killed on maintenance costs. When the membrane gets clogged, how do you replace it cheaply? How do you repair/replace damaged/

I think you’re still going to get killed on maintenance costs. When the membrane gets clogged, how do you replace it cheaply? How do you repair/replace damaged/worn out pumps? What about sections of pipe and the fittings? All of these sorts of repairs are also required for land-based water treatment facilities, of course, but now you have to perform them all at 230m underwater. That’s gotta be mega-expensive. Furthermore, all of your equipment needs to be able to survive at those depths, with saltwater attacking exposed surfaces and seals, requiring much more expensive materials and tighter tolerances. It really doesn’t seem very economical to me!

irrational 3y ago
Is economical important? If we really are desperate for fresh water, does the cost become immaterial?
- chongli 3y ago
  It’s not just that it’s expensive, it’s also ridiculously complex. About the only thing I can think of that would be more complex is launching rockets into space in order to collect water from comets.
- function_seven 3y ago
  Yes, economical is always important. In this case, we’re comparing a 231m deep unit with the “boring” existing design, and finding it less economical than the current designs.
- deleted 3y ago
  [deleted]
- kelnos 3y ago
  Cost is never immaterial. We look at the various ways we have to provide fresh water, and do whatever is cheapest. If shipping fresh water from places where it's abundant to places where it's scarce is cheapest, we do that. If/when that becomes expensive enough to make desalination attractive from a cost perspective, we start doing that. If the >230m below the surface idea turns out to be cheaper than surface level plants, we do that. But I don't think anyone really knows for sure if the underwater method could be cheaper, so we're all just guessing here. I think a good analogy for this is oil extraction. These days we extract oil from places where it's more expensive and difficult to do so, because we can no longer meet demand with the cheaper options (many of which have simply dried up over time). But we'd never go after the expensive-to-extract oil 40 years ago (or whatever) when cheaper options were available that could meet demand.
stereo 3y ago
When your straw gets clogged with ice cream, do you dip your fingers into your milkshake to unclog it? You add your osmosis filter at the end of a long flexible hose. For maintenance, you reel it back in.
- chongli 3y ago
  Straws don’t work beyond 10 metres. You need all your pumping equipment either at the bottom or distributed along the pipe. Either way, that’s going to put a ton of strain on your “flexible hose” when you try to reel it back in. And what if it breaks? Oops!
  - Enginerrrd 3y ago
    I mean, we do it with oil. ...At least sort of. Usually the wells are pressurized so pumping isn't a concern, but there's a surprising amount of infrastructure involved down at depth and the maintenance of that infrastructure is significant but largely a solved problem. Obviously economics probably favor it when oil is $75/barrel compared to ~$3 maybe for the fresh water, but still.
    - chongli 3y ago
      Your estimate for the water is way too high. I pay $2 USD (as of today's exchange rates) for a cubic metre of water from my local utility. That works out to about 32 cents per "barrel" of water. A $75 USD barrel of oil is 234 times as expensive as the same amount of water. From what I can gather, oil rigs have profit margins below 20% (at best) and margins decline as the pressure in the well head drops, until they become totally unprofitable and shut down to wait for oil prices to go up. Water prices would have to increase by more than 2 orders of magnitude to make this strategy begin to approach profitability!
      - jjav 3y ago
        > I pay $2 USD (as of today's exchange rates) for a cubic metre of water from my local utility. A cubic meter is ~264 gallons. Here in my area of California (CA has lots of water agencies, so YMMV) 1000 gallons costs $38.66 (varies based on total consumption). So that's $10.21 for a cubic meter.

irrational 3y ago

Is economical important? If we really are desperate for fresh water, does the cost become immaterial?

chongli 3y ago
It’s not just that it’s expensive, it’s also ridiculously complex. About the only thing I can think of that would be more complex is launching rockets into space in order to collect water from comets.
function_seven 3y ago
Yes, economical is always important. In this case, we’re comparing a 231m deep unit with the “boring” existing design, and finding it less economical than the current designs.
deleted 3y ago
[deleted]
kelnos 3y ago
Cost is never immaterial. We look at the various ways we have to provide fresh water, and do whatever is cheapest. If shipping fresh water from places where it's abundant to places where it's scarce is cheapest, we do that. If/when that becomes expensive enough to make desalination attractive from a cost perspective, we start doing that. If the >230m below the surface idea turns out to be cheaper than surface level plants, we do that. But I don't think anyone really knows for sure if the underwater method could be cheaper, so we're all just guessing here. I think a good analogy for this is oil extraction. These days we extract oil from places where it's more expensive and difficult to do so, because we can no longer meet demand with the cheaper options (many of which have simply dried up over time). But we'd never go after the expensive-to-extract oil 40 years ago (or whatever) when cheaper options were available that could meet demand.

stereo 3y ago

When your straw gets clogged with ice cream, do you dip your fingers into your milkshake to unclog it? You add your osmosis filter at the end of a long flexible hose. For maintenance, you reel it back in.

chongli 3y ago
Straws don’t work beyond 10 metres. You need all your pumping equipment either at the bottom or distributed along the pipe. Either way, that’s going to put a ton of strain on your “flexible hose” when you try to reel it back in. And what if it breaks? Oops!
- Enginerrrd 3y ago
  I mean, we do it with oil. ...At least sort of. Usually the wells are pressurized so pumping isn't a concern, but there's a surprising amount of infrastructure involved down at depth and the maintenance of that infrastructure is significant but largely a solved problem. Obviously economics probably favor it when oil is $75/barrel compared to ~$3 maybe for the fresh water, but still.
  - chongli 3y ago
    Your estimate for the water is way too high. I pay $2 USD (as of today's exchange rates) for a cubic metre of water from my local utility. That works out to about 32 cents per "barrel" of water. A $75 USD barrel of oil is 234 times as expensive as the same amount of water. From what I can gather, oil rigs have profit margins below 20% (at best) and margins decline as the pressure in the well head drops, until they become totally unprofitable and shut down to wait for oil prices to go up. Water prices would have to increase by more than 2 orders of magnitude to make this strategy begin to approach profitability!
    - jjav 3y ago
      > I pay $2 USD (as of today's exchange rates) for a cubic metre of water from my local utility. A cubic meter is ~264 gallons. Here in my area of California (CA has lots of water agencies, so YMMV) 1000 gallons costs $38.66 (varies based on total consumption). So that's $10.21 for a cubic meter.