It seems to be common knowledge among bakers that salted butter has a higher water content than unsalted*. How much higher?
And if there's a different amount of water, why does this nutritional data say there's the same amount of fat in salted and unsalted butter? (I'm fairly sure I've seen the same on butter in the store, and I'll try to remember to confirm that next time I'm there.)
*I'm pretty sure I remember seeing the claim several places online, but the one I was able to quickly find is from Cook's Illustrated (click to expand the second-to-last question) via an answer here, saying that "salted butter almost always contains more water than unsalted butter". (It's possible that a lot of other people's knowledge ultimately came from there.) The nutritional information I've found, along with my own baking experience, does not back this up, but Cook's Illustrated is generally pretty trustworthy, hence the question.
Salted and unsalted butter can be used interchangeably.