How can anyone help anyone out when an entire zip code loses water? And I don't think people understand just how much clean water our society uses, especially in the food supply chain.

Sure if there's a mix of homes with and without salt water. However i think you're wishful if everyone is surviving on bottles. You can only help your neighbor if you went to the store and bought water. And that supply would go quickly.

You can desalinate it with a solar still rather easily..

You only need a kids paddling pool, a bucket, a (clean!) tarp and a brick.

:)

How many people can survive from each one of those setups?

Fair, i was mostly commenting on the scenario that the GP seemed to create.