Desalination is sufficiently cheap to not be a material problem for US consumers (or other developed countries). State-of-the-art desalination plants in Israel are fulfilling contracts at ~$0.40/m^3 [1] and the per-capita water usage in the US is ~1200 m^3/yr [2]. Even if we assumed that the current price of water is $0, this would only amount to a $480/yr increase in expenditure per American which would constitute a one-time 1.4% increase of yearly expenditure for the median American. Note that this accounts for all agricultural production in the US; if we consider just water for domestic use such as drinking, bathing, and watering the lawn the average person only uses ~100 m^3/yr [3] which is ~$40/yr which is within reach of every household. This also assumes that increased water prices will not result in changes to water usage which is very doable as the US uses ~3-4x as much water per capita as other peer countries such as France and Germany and 10x the water of Israel which already needed to adjust to a regime of desalination water prices.

All in all, considered merely in economic terms, desalination is a perfectly viable solution to the water crisis in developed countries and would incur at most a relatively minor economic impact by this analysis. Note that this does not necessarily apply to developing countries where a $40/yr expenditure increase could be catastrophic. I am also not making any statement about non-economic considerations such as possible effects on the environment that may occur as a result of the need for increased power generation for mass desalination.

[1] https://www.globenewswire.com/news-release/2020/05/27/203950...

[2] https://www.statista.com/statistics/263156/water-consumption...

[3] https://www.epa.gov/watersense/statistics-and-facts

So... the average person in Israel actually spends less on water (even though it is more expensive) because they use less?

That is remarkable.

Your analysis above is remarkably detailed, but it misses the point. When I used the term "sustainable" I was speaking of resource usage and environmental impact, not whether the practice was affordable.

We aren’t going to run out of seawater anytime soon

The resource constraint that matters for desalination right now is not obviously seawater. It is the energy input for desalination, which in many areas still depends on hydrocarbons.

Why would desalination be unsustainable? The limiting factor is electricity. And renewables continue to deliver Moore's law like improvements in the price and quantity of electricity, without any environmental externalities.

I actually think that desalination and solar are a good pairing but

> without any environmental externalities

doesn't sound quite right to me. In particular I think there are reasonable concerns regarding lifetime energy and environmental costs of solar panels, mining of and disposal (or recycling) of the rare materials used in the panels, etc.

TANSTAFL

> Why would desalination be unsustainable? The limiting factor is electricity.

Disposal of the extracted salt is a serious issue. You can’t just inject brackish water back into he ocean as it screws up the ecology of the near shore environment (or wherever else you’re willing to squirt it.

Most desalination plants do just inject saline water back into the ocean. There's no where else to put it. In most cases the outflow pipe runs some distance offshore into deeper water to reduce the environmental impact.

Actually, you can. It messes with very local ecology a bit, but is otherwise a drop in the ocean.

I love this comment :) Messing a bit with drops in the ocean is how we got here in the first place.

Aggressive farming messes with the environment a bit. There is just so much land, we can't possibly deplete all of it.

Did you see how much air we have? Yeah burning dirty stuff pollutes it, but then the wind blows and it's clean again.

> There is just so much land, we can't possibly deplete all of it.

Given that we are currently using 40% of the world's land area for agriculture, and that we are using ~0.0003% of the world's water, I don't think this is a fair criticism of my post. Only a fool would think that former isn't something to keep an eye on.

> I love this comment :) Messing a bit with drops in the ocean is how we got here in the first place.

No, we got here in the first place by messing with carbon and water and nutrient cycles that take tens of millions and hundreds of thousands of years to cycle through.

The atmospheric water cycle, on the other hand, operates on a scale of weeks. Seawater gets separated into brine and fresh water, fresh water irrigates crops, fresh water evaporates into clouds, clouds precipitate over the ocean. All of humanity's historic water consumption is quite literally a drop in the ocean. [1]

The volume of the oceans is 1.3 * 10^18 m^3. Humanity's annual consumption of fresh water is 4 * 10^12 m^3. Annual worldwide precipitation is ~5 * 10^14 m^3.

> Did you see how much air we have? Yeah burning dirty stuff pollutes it, but then the wind blows and it's clean again.

[1] Meanwhile, all of humanity's carbon emissions dwarf the ability of natural carbon sinks to absorb - because in hundreds of years, we have released carbon that took tens of millions of years to accumulate. The atmospheric water cycle operates on an entirely different scale. [2]

[2] The orders of magnitude between the unsustainability of <carbon use>, <land use>, <freshwater use>, and <seawater use> are each ~two orders of magnitude removed from eachother.

It's not the use of water that's the problem, it's the releasing of the brine. This will destroy the local ecosystem and historically we haven't been able to predict the consequences of that at all.

Why does desalination produce brackish water (this is a new term to me)? From context I expected "brackish water" to mean water that is saltier than seawater. But when I look it up, it's apparently water with salinity between fresh water and seawater.

definitions aside you should be able to understand that if you add salt to ocean water it will be saltier, not less salty, than it was before