How do water heaters work?

[Aaron Fude]

OP here. Yes, that's what I am asking and I am still at a loss.

[mm]

Each horizontal pipe is too small to take the water from the larger pipe, which is bigger but more importantly, the water supply is for all practical purposes, unlimited. So all the horizontal pipes get filled. Then the right side pipe is big enough to accept all the water that comes from the horizontal pipes. So there is flow in all the horizontal pipes.

That's my story and I'm stickin' to it.