I was making a monster farm in the sky when I noticed that the water was moving very little 

Youtube Link

It's not just a problem with water, it's also a problem with redstone and many other things.
(at the beginning I thought it was my processor that's why I put it in the video to show that the problem doesn't come from there)

I watched the video again and I think maybe it's the chunk ticks that are slowed down because the water below is also slowed down near the waterfall