Modding Discussion Liquid Impermeable, Solid Permeable Blocks?

Stop me if you've heard this one before. I'm trying to find blocks that only keep liquids (like water) from going through them but let solids (like people) go through.

The whole idea stemmed from an attempt to make a river in the sky, though I just realized it would be of obvious use to airlock design too.

I presently have no idea how to make this sort of mod, as the most I've learned so far is how to make recipes for existing items. I am open to learning more though.

Anybody have any idea how to go about making this? Or has it been done already and I just missed it?

(And yes, I'm aware that probably isn't the best use of the word permeable. Advice on a better title would be nice too.)

 

I'm very noob about modding on this game for now , but infact you ask something who work like platforme but i the others way ?

If its the case maybe you can find how they work then trying to reverse theirs mechanic ? (but if you can and if it work , people will still be able to go through with Down key maybe , so they arent truly blocked).

It's only an idea , sorry if it cant help you.

Edit : I know magic staff with attraction and replusion affect dropped item and players/mob/Npc , not sure about water but maybe it can help too , idk :/