Naval Architecture
"It’s worth stressing that in these static cases the pressure at a given level depends purely on the height of the body of water."How did I not know this? It's so counter intuitive that a thin column of water can cause the same pressure as a wide one.The video they link shows this in action: 
https://www.youtube.com/watch?v=EJHrr21UvY8One mind bending fact she shares in the video is that a thin layer of water, touching the damn wall, is the same pressure as an entire lake.