Where did the phrase so am i it must be salt water originate?

The phrase "So am I, it must be salt water" is not a widely recognized or documented phrase. It is possible that:

* It's a misremembered phrase: The phrase might be a misremembered or slightly altered version of a similar expression.

* It's a regional saying: The phrase might be a colloquialism or slang expression used in a specific region or community.

* It's a made-up phrase: It's possible the phrase is entirely fictional.

If you can provide more context:

* Where did you hear the phrase?

* What was the situation?

* Who said it?

This would help determine if the phrase is real or a misinterpretation.