Fall into the water or in the water?

[ROBINDESBOIS]

Can we use both? Is there a difference?
Why then go in the water and not into the water?

[Rusty]

Both can be used, and I don't detect a difference. It comes down to how it rolls off your tongue which one is said.

[reverser]

"Fall into the water" means to fall from some place not in the water into the water. "Fall in the water" means you are already in the water and you fall. That is why I suggest you go into a pool and not "go" in it. (In American English, to "go" in a pool means to urinate or defecate in it.) Also, you may jump into a shower, but I don't recommend that you jump in it. If you jump while in a shower, you will probably fall and crack open your head. You can hop into a car but not hop in it. There is no room for hopping in a car. You can pop any kind of food into your microwave (oven) for quick heating, but probably the only thing you can pop in it is popcorn. Into and onto suggest motion from one place to another, but in and on mean you are already there.

[Rusty]

Hi reverser, I steered away from trying to differentiate between 'in' and 'into', especially with the phrase presented by the OP, because so many of us native speakers of American English use them indistinguishably.

I believe both you and I can agree that CONTEXT is what makes all the difference.

Many of us have told someone else that we 'jumped in a car' and didn't even think that they imagined us jumping up and down or hopping in it. We've also 'hopped in a car' and sped off to the movies. We didn't jump up and down in it at all.

If your kids have been waiting to get in the pool (or 'get into the pool'), you tell them, "Jump in." Not one will think your command was something they should do after they get in the water, I assure you.
As a matter of fact, it's unheard of to give the command, "Jump into."
That may explain why there's a propensity to say, "Jump in the water."

Do me a favor and look at these images. The search was 'jump in the water'.
Next try a search on 'jump into the water' and you'll see some of the exact same images. These phrases must mean the same thing.

Don't get me wrong, I certainly understood the meanings you applied to the phrases you cited, but you needed to provide context to make your point. So did I. That's because, with context, a case can be made for using either of the prepositions. And a case can be made for using both prepositions in the same situations, with no difference in meaning.

I've jumped in the shower before. In fact, to hurriedly get ready for work, I've been known to jump in and out of the shower. At no time was I worried about cracking my head open. I split my infinitive, however.

[reverser]

Yes, you jump out of the shower, and hop out of a car.