Go With The Flow
Since at least the 17th century, people have been saying that a dubious idea or explanation “doesn’t hold water.” The allusion is to a useless container which can’t carry liquid, the same idea conveyed when calling a story “full of holes.”
Newborn babies are typically wet with amniotic fluid, so “wet behind the ears” means someone new and inexperienced. Curiously, the term “dry behind the years,” for an experienced person, seems to have been first used around the same time, but has not survived into common parlance.
A momentous life happening is sometimes called a “watershed moment.” This is a geological reference, since a watershed can be a ridge or mountain chain (like the Great Divide) that defines the direction which water flows down either side of it.
“Water under the bridge” has flowed past and cannot be recovered, so this term applies to past conflicts that may as well be forgiven, akin to “letting bygones be bygones.” This phrase is several centuries old, and seems based on the earlier expression “There’s been a lot of water under the bridge since…”, suggesting much time has passed since the earlier event. A less common variant is “water over the dam.”
The term “rain check,” for postponing something to a later date, began at American baseball games in the 1880’s. Since baseball games can be “rained out,” or cancelled due to rain, a rain check was a voucher to attend a future game in place of the rained-out match.
Think you can smell rain coming, especially after several dry days? That harbinger scent is a chemical called petrichor. This compound is a combination of oils from plants but also geosmin, an alcohol produced by actinobacteria in the soil. These bacteria pick up the pace of their decomposition work when the air gets more humid before rain and produce more geosmin, which humans can detect in petrichor and associate with rain.
What causes wet dog smell? Dogs, like many mammals, carry around lots of bacteria, yeast and other microorganisms on their fur and skin. When a dog gets wet, some waste of these little tagalongs evaporates and humans detect it.