Fresh water is scarce and the demand for fresh water continues to grow annually (growing population, growing economy, etc). Fresh water is an appreciating asset, with fixed (or reducing) supply. Increasing the supply of fresh water is beneficial for many, many reasons globally, and increasing investment into desalination will keep reducing the cost (helping developing countries also build desalination).

Getting society to "use less fresh water" is non-competitive, and at best a medium term "stop gap". The economy is competitive, it doesn't "allow for" non-competitive players. You can try to change the inertia of the economy, but you would likely fail.

Building infrastructure to increase the amount of fresh water we have on earth (without unaccounted for externalities - e.g. it should be carbon-neutral/negative) is economically competitive and as such 1. durable; 2. improves lives; 3. changes the mental-model from "wasted water" to "wasted energy" (which is a simpler problem to solve).

> I disagree that we should build desalination, even if we can "afford" it.

Spreading this message of disagreement with increasing durable, cost-effective, and carbon-neutral infrastructure because it is not cost-optimal does a disservice to the global population and the long term sustainability of the global ecosystem. Way better off with the message "I agree with building more desalination. We should also get ... to do ...".

Or just add tariffs for anything we'd like to curb export of - that's the traditional solution, and it does work. Then turn around and use the tariff proceeds to further alleviate water issues.