A new solar desalination system takes in saltwater and heats it with natural sunlight. The system flushes out accumulated salt, so replacement parts aren’t needed often, meaning the system could potentially produce drinking water that is cheaper than tap water.
It’s not quite that simple. After extracting water, matching salinity would require extracting salt or adding water. It’s not that there aren’t sources of water that can be used for salinity matching, including the output of sewage treatment, the reality is that it probably makes more sense to treat that water than to desalinate in the first place.
Extracting the salts might be a source of valuable minerals and metals, but there is still no free lunch.
As far as I know, we still would be putting stuff back that doesn’t make a good match for what we took. That means depending on the natural environment for dilution and “treatment”. That has been an ongoing problem for humanity. We’re very good at exceeding the capacity of the environment to cope with our wastes.
I completely understand the comment about perpetual motion machines, but tend to think that it’s more of a scale management problem than a strict prohibition.
I live in Vancouver BC, our drinking water comes essentially from mountain run off and snow melt in two local watersheds. We get less and less every year.
My thought is that with distillation we could use brackish/ river water, then concentrate the brine until it’s as salty as ocean water and put it in the ocean.
My thought about sewer outfalls was that adding the brine to the sewer flow should pretty much match the salinity of the source because any volume that goes into the pipes comes out of the sewers. (minus some evaporation).
As long as nobody is using drinking water for irrigation, the output does pretty closely match the input.
But my point was that we can treat that water for use and reuse. That way, the desalination is kept to a minimum.