Much more powerful in 3.5, where salt was worth as much as silver for some reason. And it was a trade good, meaning it's worth the same right next to the ocean where salt is plentiful as it is far away from it when there's no trading route available.
If you really want to make this powerful, presumably if there's more water there you just destroy some of it, so destroy only the hydroxide ions and make a Coulomb explosion with the power of an antimatter bomb.
A 9th level casting of the spell could create up to about 112.5gp if we go with the 3.5e economy(which doesn't have this spell, anyways), or only just over 1gp going off the 5e economy(it takes about 4 gallons of seawater per lb of salt, and you can purify 90 gallons casting at 9th level).
It's really not that good. Sure if you're level 20 and use all of your spell slots on it it's a decent sum of gold... but you're also level 20. Go rob a bank or something.
Salt was very valuable back in the day, helps preserve food, and is the only spice you could probably get your hands on. Add to that it being a magic component, and it would be even more valuable.
Which is worth 12.5 cp. Or you could get 3 cups of acid and fill 6 vials (worth 1 gp each) and get 150 gp worth of acid. Sell that for 75 gp because it's not a trade good like salt, and you still made a profit of 69 gp. Nice.
The spell affects 10 gallons of water at first level, leaving you with close to a pound of salt valued at 5cp. That's not going to break the bank, but assuming you spend only one 1st level slot per day every day, in a month that will earn you 1.5gp, putting you somewhere between a Modest and Comfortable lifestyle.edit: turns out these prices are per day, I can't read, and I'm going to die in poverty covered in salty rags
The prices listed on that page are per day not per month. So with that in mind 5cp per day would but you at the lowest category of Wretched. Though both level 1 slots would put you at Squalid.
Well? What happens next? The story was just getting good! Suddenly all the salt dried up and people are inexplicably dying, nearly a hundred a month. What is causing this? What happens now? Does the fact that the entire town is built on a demolished holy site have something to do with it? How does the PC respond?
And then, since it's a trade good, you can sell it at full price to whatever lives on that plane. Though the way it's worded in 5e makes it sound like that's not necessarily true everywhere. It works better in 3.5.