Various Forms of Water

You know how things come in trends? Like, someone mentions an unusual word, and for the next two weeks you overhear it in conversation, catch it in a TV show or movie, or see it in print media?

"Water" has been like that for me. Certain expressions have been coming up and I started to get them confused in my head (if I was ever clear on them). For my own clarification, I just wanted to render these here so I don't get them mixed up again.

jerkwater

Remote or insignificant.

backwater

Reservoir of water welling up behind an obstruction.

(of the) first water

Of highest value or purest quality.

The Online Etymology Dictionary suggests the first term comes from American carnival slang, a contemptuous name for small, rural settlements that had no water tank from which to refill their boilers. Instead, they drew water from any regional creek or stream.

The second definition seems clear once you see it spelled out like that, yet I don't know how I would have ever come across this term in casual conversation. No one I know has ever been overly concerned with "the section which is influenced by the conditions at [a river's] mouth."

The third has a pedigree as rich as usage by Shakespeare, and it apparently refers to the clarity of a diamond. The purest diamond should be as clear as a drop of water, then an ordinal value is added to rank the diamond from "highest quality" to "colored stone."

Not included is "greywater," about which I am absolutely not confused. This is a catch-all term for dirty, used water produced by a domestic environment, everything from laundry water to what you flush down the ter-let.