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