I'm sure many people are aware of how ... let's be honest, horribly ugly Minecraft's water can be.
In 1.13 this will partially be fixed, with partial-blocks finally having water render inside them! But previous versions, where I imagine a lot of mods will stick to for a while, have no such fix.
There is a mod that does this called AquaTweaks but it's only for 1.7.10 and the author has expressed that he doesn't believe it's possible to update the methods he used to 1.12.2.
Another mod does something similar- Optifine (I can hear the collective groan of any mod developer who likes to render stuff), which can render fake snow under vanilla blocks like tall grass and fences if they're adjacent to snow blocks.
So... I'm not sure how feasible this is but with the introduction out of the way, I propose the following mod for 1.12.2 at least:
-If a block is non-solid/doesn't have a full-sized hitbox, and it is adjacent to snow, a rendering hack will copy that snow render to the bottom of the block beside it.
-If the same is true for water source blocks, the same will apply. I'm not asking for full water physics in these places, just for it to render nicely.
-But the real kicker is that neither of these mods work for modded blocks to my knowledge. And I'm wondering if there could be a way to automatically detect and apply this to mod blocks too.
There have been all sorts of mods that do weird rendering tricks like this based on block adjacency; the aforementioned AquaTweaks and Optifine (Optifine still doing it in 1.12.2), No Cubes, which, despite being on 1.7.10, was successfully getting a port to 1.10 or 1.11 before the port's author vanished entirely. That said, I know very little of rendering and the specifics may be wildly different, and maybe there really isn't a way to do this, especially in a mod-friendly way. But I still figured I'd ask and see if anyone was willing to give it a shot.