A liter of seawater has 35 grams of salts in it (I looked it up: http://en.wikipedia.org/wiki/Seawater ). Compare that to the recommended daily intake of several grams of salt.
It's also the case that most of the desalination methods produce concentrated brine instead of dry, clean salt (so extracting the salt would require further energy), but not needing that much of it is the bigger reason.
I got that. For every liter of seawater that is desalinated, there would be ~35 grams of table salt. On a given day a person might use 4 grams of salt.
Given typical water usage, you quickly have salt for an awful lot of people (salt for hundreds of people per person consuming the water).
I guess other users would be welcome, even if they just take it for free that probably saves the desal plant on disposal costs.
It's also the case that most of the desalination methods produce concentrated brine instead of dry, clean salt (so extracting the salt would require further energy), but not needing that much of it is the bigger reason.