Smart people already know that that is not an economical way to get water.

Besides, the problem is more regulatory than physical.

We already have one nearly finished in San Diego. The problem is that is makes for very expensive water because it's a large scale industrial desal plant and the technology still hasn't changed in such a way as to not require lots of energy. That said, it's still at least going to provide a huge amount of water with just the one plant so there is that.

Personally I'm waiting for someone to stick a nuclear reactor far off shore, use it for both power generation and desalination at the same time and ship fresh water back to the mainland on barges.

How much of municipal water needs to be fresh water? Like if you showered with salt water, bathed in salt water, flushed your toilet with salt water etc. Then you wouldn't need to desalinate so much. So maybe, tap salt water could be viable for apartments. Then you'd have to have some domestic desalinator for those few liter's per day you actually drink. Well or buy bottled water.

Now that I think of it: Maybe you could make the hot water salt, and the cold water fresh. You aren't supposed to drink hot water anyway since it contains more dissolved nasties. And you wouldn't water your lawn with hot water because that would be like super wasteful. Although I can see how hot salt water could be somewhat corrosive so maybe you'd need to switch up the plumbing at a huge cost.

And lots of heat too.

Use some solar thermal collectors for energy (not solar electricity, use the heat to directly run a pump), and desalinate some water.