My controversial take is that the best solution will be to accept that solving the drinking water problem for people is worth worsening the environment for some local sea life.
A poorly implemented runoff would nuke a square km or five of ocean floor with high salinity waste. It would not impact food supply in any discernable way. The ocean is simply too big.
I don't think humanity is ever really considering environmental impact unless it impacts it somehow. We care about disappearing species which amuse us, which we can see at our scale level, not much below. Some rare lion? Tragedy! Thousands species of fungi living underground which don't impact us directly? Irrelevant. Same goes for climate change and others. We only care if it impacts us in any way, even if only our entertainment.
So long story short we probably care about sea life.
> Or just sell it as salt? We use, I don’t know, billions of pounds of salt per year in food production?
Are you sure the math even remotely checks out? Just looking up some numbers, even if we naively assume ocean "saltwater" is just H2O + NaCl (which it obviously isn't): the world consumes around 300 billion kg salt/year, whereas (say) Los Angeles alone uses 700 billion kg water/year. So even if a city like LA provides for the whole world's use of salt, what does everyone else do?
I'm sorry, perhaps my engineering education makes me handwave at problems -- but the water we're desalinating has to return to the ocean someway, it's not like we throw it into black holes, why can't we just dump the brine 20 miles into the ocean, the water we've desalinated will return by other means.
"Could have" is doing a lot of heavy lifting there. Assuming spherical cows, 12 is an upper limit, okay. What you could actually do is neither remotely close to that nor is that itself remotely close to what the world needs, was the point.
You’re assuming we need to get 100% of our water from desalination when it would only need to cover any shortfall from other methods. We’re currently getting 100% of the water we need from those other methods.
Really depends who "we" is. Israel gets 75% of its water from desalination already, and that's just right now. And a lot of the other water sources right now are nonrenewable (groundwater, etc.), hence a big part of the motivation to look for new ones in the first place. The current situation is not sustainable on its own in many parts of the world, let alone the effects of dramatically increasing population sizes and global warming.
Further concentrated salt solutions deposit in the device, clogging it causing it to not work. You could harvest the salt, but then it is no longer passive.
