I think the original meaning is to pour (hot) water over yourself

The original verb was 浴(あ)む, and it went 浴む > 浴ぶ > 浴びる

And then it gained the more general meaning of bathe in

Sorry, that's about the best I can do, you can always get an explanation from someone else :-)

@Chris If you want to learn Japanese, your goal has to be talking like Japanese people do. Otherwise, you're making up your own language instead.

You learn the phrase as a unit. You can't learn words in isolation.

Language doesn't work that way. How would you know to "take" a shower? Where are you taking it?

How do you know you arrive at a place instead of arriving to a place? They both make an equal amount of sense, but only one is grammatical. You just have to learn that people talk that way.