So I had the occasion to talk a little bit with Jeb, and he told me more about the 1.14 upcoming aquatic update functionnalities, including how the new water will work.

"The things that we showed at Minecon may have been too much, so we're trying more simple way of doing the water physics, more similar to the old style. The most important thing is to have non solid blocks inside water, like stairs and fences, but the way we're gonna do it is that if you have a fence and you put water on it, that's gonna be a water source block, but water itself won't flow through fences [...] because that would break a lot of contraptions that people make using trapdoors and such."

"We want water physics to work like they do today. The difference is that you can put water on the fence, and then the fence will be inside water"

You can hear more about this on this livestream at 1h47m10s : https://mixer.com/jebkhaile?vod=16775563