James Dreben 
#ELI5 Why is water see through?
I'd never thought about it like this. Wow.
CavyherdSee also (heh) air
Okay, here's one: why do both air & water pass as many of the same wavelengths as they do?
Where do they (or do they?) differ & why?
The_LazyKnight@cavyherd @Jdreben eyes evolved to process wavelengths that can pass through both water AND air: not either/or, but both...
A good counter example is near IR and coke: coke doesn't pass visible wavelengths, but does pass IR, as does air. Stick an IR pass filter in front of a camera and you can take a photo *through* a pint of coke.
😂 TIL about Coke!
But my question was a little different: it wasn't about why the eye can see through both water & air—that was very nicely covered in your first response.
Rather, why are both air & water transparent to the same wavelengths (or at least a large overlap in the range that we can also see)?
For that matter, why is Coke NOT transparent in that range? (One presumes this has to do with transmission/emission spectra.)