Hi, it's nice to see you liked it. Thank you.
As for your question, I didn't try it the way you did before but it's possible to see that result. In theory, since I created the material double-sided, it renders both faces but doesn't create geometry for the inside. If you create new material and make Render Face - Both, without using the shader, you probably will see the same result. (If I understood your problem right.)
To see more realistic results, you can do some research on fluid simulations.
For simulating fluids I have tried something before. Here's my repo for that. https://github.com/ereneker/Fluid-Simulation
Though I never done rendering part since I had to learn more about compute shaders that time. If you want to do something like that, I'd suggest you to watch Sebastian Lague on youtube.
I'm currently moving to a new place so won't be able to look at it for a couple days. Later, I might look into it and try to figure a way to do that with shader. I'll update the asset if I find something.