system
Given the following post, respond as if you're commenting on Reddit:
human
What happens when you compress water?

I hear a lot that water is incompressible. But it must to some degree. 

Hypothetically if you take the mass of two planets and make them collide with a litre of water in the middle, what would happen? 

When people say water is incompressible, I take it as such. Can a litre of water really support two planets? Seems too far fetched. Please ignore the container and all little nitpicks such as this.
gpt
You don't need to collide two planets to compress water. You can just put it in a pressurized chamber, or go to the bottom of the ocean.

Water is incompressible for most engineering applications, but it definitely compresses. It compresses by about 2% at 4 kilometers under water. If you put it under more extreme pressures, you get different types of ice that form.