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.
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.