Purify Food and Drink and sea water

[Scalenex]

I know the spell can let adventurers get potable water from a muddy stream by the road, but what about seawater?

Does the 0th level spell create a quantity of drinkable water or does it create a quantity of sparkling clean saltwater?

I don't think even in a high magic setting, a large population center can rustle enough low level clerics to manage a large population's entire water supply, besides not everyone would want it. Making water safe to drink if a fantastic excuse to make alcoholic beverages. A low level cleric should be able to produce enough water for a large cargo vessel or small warship, so said ship can probably sail much farther because they don't need to carry as much water or make as many supply stops. That has implications for shipping, infrastructure, and communication that lets an empire manage farther holdings.

Second question. Does the Purify Food/Drink spell make contaminants disappear or does it dump them out in small pile nearby? If the orison can desalinate sea water, then it can also be used to manufacture quantities of sea salt faster and possibly cheaper than the medieval tech solutions of boiling seawater or leaving big vats of sea water to evaporate in the sun. It'd be of mild interest to world building if people bought their salt from the local temple.

When the elders make the aolytes fetch the temple's water in the morning, might as well make them collect some salt too.

[Jormengand]

Create water just creates water. It doesn't create water with salt in it, just water. Purify food and drink works on "Otherwise contaminated" food and drink, which probably includes sea water.

The purify food and drink spell doesn't actually alter the chemical composition of the stuff or even make it taste different, it just overrides the normal effects of what would happen and makes it safe instead.

[Sagetim]

Considering that Salt is a trade good worth 5 gold to the pound, being able to filter it out of sea water using purify food and drink would provide a means of obtaining a steady supply of it with a minimal of labor.

I think it comes down to how your GM decides to interpret the spell working, though. I wouldn't have any problem with having the spell filter out the 'not water' components into a pile nearby, but another GM might interpret that the spell eliminates those impurities entirely, leaving just the pristine water. While Jormengand seems to be of the ruling that the water isn't changed, it's just magically safe to drink.

It seems entirely reasonable for clerics (who tend to be of above average wisdom, since it's their casting stat and all) would notice that they could filter salt out of salt water and sell that to others. While they aren't going to necessarily make a huge business out of it (and probably won't be using all of their limited daily orisons on purify food and water), it wouldn't be unreasonable for sea side temples to have a steady supply of salt, which they might pass out among the congregation as a benefit for being part of the faith, or they might sell to supplement their coffers.

What I think would be unlikely, however, is for the clerics to take it in an economic direction, such as by crafting a magic item to cast purify food and drink on command, then hauling up sea water en masse to filter out the salt and provide potable drinking water for the community as a whole. That seems more along the lines of something that should be left to player scheming and innovation.

[Elkad]

If it does remove the salt, that's 10gp/casterlevel for seawater (at 3.5% salt concentration).
A saltwater lake may have 10x that amount.

And now I'm reminded of the "Freshened Sea" in the Wizard's Bane books.
Demon set (by a foolish mage) to remove all the salt from the sea, but not told where to put it, so it piled it around the sea, burying all the towns.