- May 19, 2011
- 21,103
- 16,315
- 136
I don't know why the expression popped into my head, but referring to someone or something as being "a ... of the first water" (to mean that it's an extreme example of its kind), apparently dates back to rating diamonds: the more translucent (ie. like water) they are, the more they're worth. If a diamond is of the first water, it's the most valuable kind.
