So, this series of paintings actually has a whole bunch of lore behind it in the descriptions - it seems to be set after some kind of climate catastrophe, and a bunch of the paintings are covering various efforts to tackle it. From the description of this specific one (with a very clunky machine translation):

China’s coastline will return to the level before the glacier collapse; after that, these large desalination hubs only need to run at full capacity on a regular basis to stabilize and replenish Tarim Lake, Qaidam Lake and other east and west water [the translation butcheted this part, maybe it was meant to be "eastern and western lakes"?]

The water level at the destination of the diversion project will be in an unsaturated state for most of the rest of the time, providing some fresh water along the line as a flexible supplement for local production and domestic water. Even so, the work of Lao Liu is not easy: the maintenance of the halophyte purification pool and the operation of the system terminal are inseparable from them.

The next painting in the series mentions:

in 2066, a plan to pump water from the Great Western Basin and the embankment to restore China's original coastline was put on the agenda. The plan to divert water to the Western Great Basin was called " "Water diversion from east to west", the seawater will first be processed by the seawater desalination hub to become clean fresh water that meets safety standards, and then it will be lifted step by step along the aqueduct under the push of the pumping station, and run westward all the way;

The situation seems to have been pretty bad - "glacier collapse" doesn't exactly sound nice, and apparently China's whole coastline got wiped out by the rise in sea levels. Some of the other paintings talk about massive "immigrant cities" having to be built to house all the people displaced by the flooding. It seems like they they're trying to restore the coast, and deciding that they might as well make use of the water that they're pumping out by desalinating it. After the process is done, the plants will be reduced to running at lower levels.

I'm not sure about the tech behind this and how sci-fi the concept actually is, but I guess the ocean enviroment is already kind of fucked at this stage. There's some talk of embankments, so it might be that they've walled off the section of the ocean covering what used to be Eastern China, and are only pumping out and desalinating it while not touching the rest of the ocean. I'm not sure, I haven't read all of the descriptions (and I can only read them through shitty machine translation, which isn't always comprehensible)