When you're peeing in the toilet and some liquid splashes out, is that pee or water?

It's both.

Here's a video of a water droplet, and you can see water (or urine) can actually bounce off the surface: https://www.youtube.com/watch?v=pbGz1njqhxU

And here's a simulated urine stream: https://www.youtube.com/watch?v=9c66KVU5ah8

The urine displaces a lot of nearby water as well. That surrounding water would initially be "clean" toilet water, but urine will mix into the water pretty quickly. That mixed water will then also displace as more urine hits the surface.

Probably a little column A, a little column B

depends on the force of your stream and how close you are to the surface of the water

You could taste some and find out?

According to this law, nothing has independent, permanent, or absolute existence. Everything is part of a limitless web of interconnections and undergoes a continual process of transformation. Every appearance arises from complex causes and conditions, and in turn combines with others to produce countless effects. By interrupting the causal chain at certain key points, the course of existence can be altered and effects prevented by eliminating their causes.

https://www.lionsroar.com/dharma-dictionary-interdependent-origination/