Coast-side desalination seems like it would reduce this issue to be less critical of a zero-sum game.

Cost makes it still essentially zero sum, unless we get actual cheap fusion off the ground anyway. Very few countries can afford to use water from desalination at any scale, and even for them the cost of it is an order of magnitude or more than using existing runoff - when the runoff exists.

That alleviates drinking water. These are agrarian communities. It’s like proposing desal to irrigate the San Joaquin valley —expensive!