system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: If water can't be compressed under normal conditions, then how does water pressure work?
gpt
Water is compressible, just not by very much. For example 4 km under the ocean, water’s density is increased by just 1.8%. This is so small that saying water is in-compressible make for a good approximation.
  

  
Pressure does not depend on how compressible a substance is. It just depends on the total weight per unit area of all the substance above, pressing down.