It's obvious why we don't drink it.
But... What's the long term cost on desalination vs building a secondary water distribution network? There's no reason we can't shower in filtered salt water, no reason we can't flush toilets with it, no reason we can't wash cars with it. No need to maintain residual chlorine in it, either, just disinfect it at the source. Want a swimming pool? Fill it with salt water (salt water pools are becoming more popular anyway, they're apparently cheaper to chlorinate). Hook it up to all the outside faucets, and if anybody tries to water their lawn, it'll either be self-defeating or they can switch to salt-tolerant grasses.
I'm sure plenty of industrial processes could run on salt water too - certainly not all of them, but I'd bet it's a large chunk.
It's not a solution where the runoff and treated sewage end up in freshwater rivers, but for cities that drain into the ocean, it's not a problem.