[ptha]

Desalination is not without problems, producing 1 to 1.5 times the amount of brine (compared to fresh water) being one of them. How to dispose/use this brine. There are some options: https://news.mit.edu/2019/brine-desalianation-waste-sodium-h...

[jillesvangurp]

Sounds like a nice engineering challenge but not a show stopper problem.

Also this seems like it would be more of an issue in shallow waters than it would be in open ocean. A simple pipe to deeper waters probably goes a long way to fixing things. The Pacific is pretty deep near the Californian coast and has strong currents too. The volume of water moving through that is probably many orders of magnitude larger than any brine you can dump there. So, unless I'm very wrong about this, I'd expect things to dilute pretty quickly.